November 2011 Cover Page

  November 2011
  
The Rifleman's Journal
A Collection of Articles Dealing with Rifle Accuracy Topics


This Month:
Hap Rocketto - Hap's Corner
John Lowther - Barrel Chambering
Scott Harris - Sartorius Balance
Germán Salazar - Rifles and Reloading


15 Cents 

The Desolate Wilderness and The Fair Land

On this Thanksgiving Day, we bring to you these two pieces, one from the 17th century, one written by the great Vermont Royster in 1961 as a companion to the first.  Mr. Royster won the Pulitzer Prize for editorial writing in 1953; his editorials in the Wall Street Journal influenced generations of freedom seeking people.  Having come to this country from another, as did the Pilgrims, these two pieces have always had a special significance for me.  The power of Mr. Royster's words remains undiminished by the passing of time and I suspect they will retain that power for as long as people seek a better life than the one they willingly, though painfully, leave behind.    
- GAS -

The Desolate Wilderness
Here beginneth the chronicle of those memorable circumstances of the year 1620, as recorded by Nathaniel Morton, keeper of the records of Plymouth Colony, based on the account of William Bradford, sometime governor thereof:

So they left that goodly and pleasant city of Leyden, which had been their resting-place for above eleven years, but they knew that they were pilgrims and strangers here below, and looked not much on these things, but lifted up their eyes to Heaven, their dearest country, where God hath prepared for them a city (Heb. XI, 16), and therein quieted their spirits.



When they came to Delfs-Haven they found the ship and all things ready, and such of their friends as could not come with them followed after them, and sundry came from Amsterdam to see them shipt, and to take their leaves of them. One night was spent with little sleep with the most, but with friendly entertainment and Christian discourse, and other real expressions of true Christian love.

The next day they went on board, and their friends with them, where truly doleful was the sight of that sad and mournful parting, to hear what sighs and sobs and prayers did sound amongst them; what tears did gush from every eye, and pithy speeches pierced each other's heart, that sundry of the Dutch strangers that stood on the Key as spectators could not refrain from tears. But the tide (which stays for no man) calling them away, that were thus loath to depart, their Reverend Pastor, falling down on his knees, and they all with him, with watery cheeks commended them with the most fervent prayers unto the Lord and His blessing; and then with mutual embraces and many tears they took their leaves one of another, which proved to be the last leave to many of them.

Being now passed the vast ocean, and a sea of troubles before them in expectations, they had now no friends to welcome them, no inns to entertain or refresh them, no houses, or much less towns, to repair unto to seek for succour; and for the season it was winter, and they that know the winters of the country know them to be sharp and violent, subject to cruel and fierce storms, dangerous to travel to known places, much more to search unknown coasts.

Besides, what could they see but a hideous and desolate wilderness, full of wilde beasts and wilde men? and what multitudes of them there were, they then knew not: for which way soever they turned their eyes (save upward to Heaven) they could have but little solace or content in respect of any outward object; for summer being ended, all things stand in appearance with a weatherbeaten face, and the whole country, full of woods and thickets, represented a wild and savage hew.

If they looked behind them, there was a mighty ocean which they had passed, and was now as a main bar or gulph to separate them from all the civil parts of the world.


And the Fair Land

Any one whose labors take him into the far reaches of the country, as ours lately have done, is bound to mark how the years have made the land grow fruitful.

This is indeed a big country, a rich country, in a way no array of figures can measure and so in a way past belief of those who have not seen it. Even those who journey through its Northeastern complex, into the Southern lands, across the central plains and to its Western slopes can only glimpse a measure of the bounty of America.

And a traveler cannot but be struck on his journey by the thought that this country, one day, can be even greater. America, though many know it not, is one of the great underdeveloped countries of the world; what it reaches for exceeds by far what it has grasped.

So the visitor returns thankful for much of what he has seen, and, in spite of everything, an optimist about what his country might be. Yet the visitor, if he is to make an honest report, must also note the air of unease that hangs everywhere.

For the traveler, as travelers have been always, is as much questioned as questioning. And for all the abundance he sees, he finds the questions put to him ask where men may repair for succor from the troubles that beset them.

His countrymen cannot forget the savage face of war. Too often they have been asked to fight in strange and distant places, for no clear purpose they could see and for no accomplishment they can measure. Their spirits are not quieted by the thought that the good and pleasant bounty that surrounds them can be destroyed in an instant by a single bomb. Yet they find no escape, for their survival and comfort now depend on unpredictable strangers in far-off corners of the globe.

How can they turn from melancholy when at home they see young arrayed against old, black against white, neighbor against neighbor, so that they stand in peril of social discord. Or not despair when they see that the cities and countryside are in need of repair, yet find themselves threatened by scarcities of the resources that sustain their way of life. Or when, in the face of these challenges, they turn for leadership to men in high places -- only to find those men as frail as any others.

So sometimes the traveler is asked whence will come their succor. What is to preserve their abundance, or even their civility? How can they pass on to their children a nation as strong and free as the one they inherited from their forefathers? How is their country to endure these cruel storms that beset it from without and from within?

Of course the stranger cannot quiet their spirits. For it is true that everywhere men turn their eyes today much of the world has a truly wild and savage hue. No man, if he be truthful, can say that the specter of war is banished. Nor can he say that when men or communities are put upon their own resources they are sure of solace; nor be sure that men of diverse kinds and diverse views can live peaceably together in a time of troubles.

But we can all remind ourselves that the richness of this country was not born in the resources of the earth, though they be plentiful, but in the men that took its measure. For that reminder is everywhere -- in the cities, towns, farms, roads, factories, homes, hospitals, schools that spread everywhere over that wilderness.

We can remind ourselves that for all our social discord we yet remain the longest enduring society of free men governing themselves without benefit of kings or dictators. Being so, we are the marvel and the mystery of the world, for that enduring liberty is no less a blessing than the abundance of the earth.

And we might remind ourselves also, that if those men setting out from Delftshaven had been daunted by the troubles they saw around them, then we could not this autumn be thankful for a fair land.

The Voyeur's Guide to Barrel Chambering - Postscript

The Voyeur's Guide to Barrel Chambering - Postscript
by Germán A. Salazar

We've had a lot of email and commentary from readers regarding the Voyeur's Guide to Barrel Chambering series of articles, and John and I are very gratified that it was so well received. Hopefully we'll find another topic or two to cover in a similar fashion.

This past weekend (November 19-20, 2011) I competed in the Arizona Long Range State Championship (1000 yd.) using the barrel featured in the series. I was shooting in the F-TR category in deference to my still recovering shoulder, and it was my first F-Class match at 1000 yards.

To make a long story short, over two days of shooting, 1200 possible points in typical windy Arizona desert conditions, I won five of the six stages, was second in one stage by three X's and won the F-TR aggregate by a fairly wide margin. I also finished ahead of all the F-Open competitors except the winner Dave Gosnell who beat me by an large margin.  I don't have a copy of the final results in front of me, so I don't want to quote exact numbers.


John Lowther and Oliver Milanovic
 I say this not to brag, we all know that there's no real glory in this sport, but to emphasize that John's work was second to none in the results it produced. As we said in the article, there are many ways for a machinist to approach the various tasks involved in producing a good barrel chambering job and I am more than satisfied that John's approach is the right one for me.

Equipment: Sartorius GD503 Evaluation

Sartorius GD503 Evaluation
by Scott Harris


Bottom Line Up Front
The Sartorius GD503 is a superb scale and has delivered what I am looking for: increased reloading speed and increased precision. My old setup allowed me to measure to +/- 0.05 gr. at a rate of one charge every 27 seconds on average. The new setup allows me to measure to +/- 0.01 gr. (fraction of a kernel) at a rate of one charge every 19 seconds. I already had $1000 invested in my old setup; so, moving to the new Sartorius GD503 a big decision. Alternately, the $300 Sartorius AY123 is an excellent choice and I would not hesitate to go that route if I were on a tighter budget.

Introduction
Sartorius recently introduced a new scale that may be of interest to reloaders. An excellent review on this product on AccurateShooter can be found by clicking here. Rather than re-hash info found in that article, I want to evaluate the new scale using criteria important to me as an F-class shooter and as the primary reloading “mule” for a family of 4 and sometimes 5 shooters. Here are my priorities:

1. Speed: We shoot just about every weekend and loading 300 rounds per week can get a bit tedious. Anything that makes the process faster is of interest. Time is money and I’m willing to pay up if the time savings are there.

2. Precision: I already have a great setup that measures consistently to +/- 0.05 gr. It would be nice to see a significant improvement over that level of precision with no increase in reloading time.

3. Reliability: I’d like a piece of equipment that is reliable and long-lasting. For $900, I want a scale that will last many years if I take good care of it.


Comparing the Old and the New


Old Setup
My old setup, as shown in the picture above, consisted of two RCBS Chargemasters and one Acculab VIC-123. The Chargemasters would pre-weigh the charge at the exact target weight I was shooting for. Then I would perform a final weigh on the VIC-123 with whatever small adjustments were needed: either trickling a few kernels in or taking a few out with my fingers. Using this method, I could achieve accuracy of +/- 0.05 gr. at an average speed of 27 seconds per charge. It was possible to get a little more precise, but it would take much longer to weigh each charge - too long.

PROS of Old Setup
1. Accurate: +/- 0.05 gr.
2. Fast: 27 seconds per weigh
3. Repeatable: Using a check-weight at various times over many months, I have consistently demonstrated the Acculab is an accurate, repeatable scale.

CONS of Old Setup
1. Three devices: I need two Chargemasters to keep me from twiddling my thumbs. This takes more space.
2. Noisy: Some people might perceive the whir of the Chargemasters as music to their ears - not me.
3. Drift on the Acculab VIC-123: To use this scale properly, you must re-zero the scale regularly; often every time you weigh a new charge. This is not as big a deal as it sounds but the process could be faster if this step were not required.
4. Acculab is sensitive to environmental variables: To get the most out of this setup, you must warm up the scales for at least 30 minutes, eliminate all drafts by turning off the heat or air conditioning, and eliminate electrical surges by turning off other electric devices.

OVERALL Assessment of Old Setup
It works well once you understand the nuances of the Acculab scale. The new Sartorius GD503 will need to make a big impression for me to change my system.

New Setup


New Setup: Equipment
1. Sartorius GD503 purchased from balances.com (great folks, they pre-programmed it by emailing me and setting it to weigh in grains).
2. Omega Power Trickler: You can trickle single kernels with ease.
3. Lee Perfect Powder Measure: You can spend a lot more money on a measure but you won’t get one that is better. I owned a $250 Harrell’s Premium Power Measure, but prefer the $20 Lee.

PROS of New Setup
1. Faster: 19 seconds per chatge vs. 27 seconds for the old setup
2. More Precise: I am now measuring to +/- a single kernel of powder. The GD503 can measure to a small fraction of a single kernel in weight and it does this very quickly. The VIC-123 can only measure to the nearest whole kernel or two.
3. No Drift: There is essentially no drift if you let the GD503 warm up for at least 30 minutes. This means you can perform and extended weighing session without the need to re-zero the scale.
4. No Added Cost: Compared to my old setup, the GD503/Omega Trickler is no more expensive.
5. Quiet: No more noisy RCBS Chargemasters. I know, this is a nit-picky comment.
6. Less Space: 3 scales have been replaced with one scale and a trickler.

CONS of the New Setup
1. Reliability? $900 is a big investment for a single piece of electronics and I hope this scale proves to be reliable for many years - time will tell.

Video Demonstration

Here is a short YouTube video I created:

The Voyeur's Guide to Barrel Chambering - Part 5

The Voyeur's Guide to Barrel Chambering - Part 5
by Germán A. Salazar and John Lowther

 The muzzle end of the barrel requires less work than the breech end, but it is by no means unimportant. The crown of the barrel is the last thing to touch the bullet until it bores it's way through the target paper 1000 yards away - and any imperfection will set it on a course other than the one you intended.  Therefore, although we're near the end this is no time to rush.


Photo 33 - Cutting off the muzzle end of the blank

Muzzle Cut-off
We begin by cutting off the last couple of inches of the barrel. The last inch or so is always a little oversize in its internal dimensions due to the reversing action of the abrasive coated lap used in the finishing process at the factory. Additionally, I wanted the barrel to finish at 29.5" rather than the usual 30"; the reason was simply to create a little margin for the 8.25 kg. weight limit in F-TR. With the previous barrel, which was 30" long (the disastrous mis-marked 1:18" twist barrel), the rifle weighed 8.20 kg. and given the possibility of varying scales, that 1/2" reduction in barrel length seemed like a prudent choice.

As shown in Photo 33, the cut-off is a simple operation, the right tool is inserted on the tool post, plenty of cutting fluid is applied and slowly the tool is advanced into the blank until the piece is removed.

Photo 34 - facing off the muzzle end after the cut off

Preparations
Next, the blank is moved out of the headstock a couple of inches and re-indicated to be on center as was done previously for the breech end. Once that has been done, a light clean-up cut is taken across the face of the muzzle.


In many circumstances, we could begin the crowning operation now. However, because I'm principally an iron sight shooter, we need to prepare the muzzle end to accept a front sight base.


Sight Mounting
Over the past ten years or so, there has been a wholesale shift in front sights from the old style that slid onto a dovetail base screwed to the barrel, to the type that clamps on via a barrel band type mount. I resisted this shift for some time as I neither wanted my barrels to have a sudden step at the end nor did I want something clamping the end of the barrel. As I mentioned in the opening paragraph, the muzzle end of the barrel is critical to accuracy and those things concerned me. However, notwithstanding my reservations, once I tried a barrel band mount, I saw there was actually no detrimental effect and all of my barrels have used that system for at least the last 6 years.
Photo 35 - Turning the muzzle end to 0.749" diameter
The barrel band mounts are most commonly found with a 0.750" inside diameter. It's usually best to turn the barrel to 0.749" diameter to ensure a close but non-binding fit.

Photo 35 shows the turning down process as it nears the end. As with all previous cuts, this operation is performed in many small passes, each ending precisely at the same point. In this case, based on the length of the front sights I use, the tenon was cut 0.749" x 1.75".



Photo 36 - Ready to crown
Crowning
The tool used to turn the outside diameter is replaced with one more suitable for facing and our attention turns to the barrel's crowning touch - the crown.


After carefully ensuring that the tool is centered, the crowning cuts begin. In this case, John was cutting a flat, recessed crown, so a series of cuts would be made creating the recess.






Photo 37 - Chips flying as the crown recess deepens
Slowly, methodically, the cutter is brought in a few thousandths deeper with each pass and stopped at precisely the same spot.
















Photo 38 - Recessed crown
After a few more passes, we have a finished crown recess. A little more can be done, many gunsmiths favor breaking the edge of the lands at a 45 degree angle and PTG sells a special tool just for that. The principal purpose of that small bevel is to reduce the possibility of the cleaning rod jag damaging the crown. I'm not too worried about that with the Bore Rider jags I use (I don't brush), so this wasn't critical to me.

John and I discussed it and I decided to shoot the rifle a little bit before we cut the bevel on the end. Part of the reason was simple curiosity as to whether it would make a difference, the other part was that the tool hadn't arrived and I'm ready to shoot!


Photo 39 - John Lowther with the finished barrel
Happy Ending
Well, it's been a lot of work for John and a lot of typing for me, but the barrel is done for now and ready to shoot. It's hard to describe how satisfying it is to see all of this work evolve right in front of your eyes and I'm very grateful to John for all of the work and for his patience with me. I managed not to stick my fingers into the moving bits and we passed John's test for a successful day in the shop: we left with as many fingers as we arrived with!

The Voyeur's Guide to Barrel Chambering - Part 4

The Voyeur's Guide to Barrel Chambering - Part 4
by Germán A. Salazar and John Lowther

Photo 24 - Chamber reamer with removable pilot bushing
Cutting the chamber can certainly be described as the heart of what we're doing, although as you've seen in the previous installments, it is far from the only operation. There is a certain sense of anticipation, however, as the breech preparations are complete and the chamber reamer makes its appearance.

Reamer
Photo 24 shows the reamer, which will be used in this project. The reamer has a pilot bushing at the front; this is removable and the gunsmith has a large selection of bushings to exactly match the bore dimension of the barrel being chambered. This is a trial fit process that requires the gunsmith's judgment as to a fit that is just tight enough to guide the reamer without play, but not so tight as to damage the lands.


Photo 25 - Reamer entering the bore
Once the correct busing is selected and installed on the reamer, the reamer is set up in the holder and inserted into the bore. In this case, there is also a special tool attached to the reamer which we'll discuss later.

The barrel will turn and the reamer will remain stationary (in a rotational sense) to make the cut. The reamer is not locked down rigidly at the rear; it is held in a floating manner, and pushed into the turning barrel slowly. This ensures that the reamer follows its pilot bushing into the bore which itself was centered in the headstock in our first operation.



Photo 26 - Reamer cutting the chamber
Slow Cutting
Just as with each cut that we've seen before, the chamber is cut with many, many passes. The reamer is cutting a lot of metal out of the barrel and the flutes load up with chips quickly. If they aren't removed regularly, they can get caught between a cutting surface and the chamber wall and leave a deep scratch which will have a very adverse effect on extraction. Consequently, the reamer is run in about 0.050", removed, cleaned, re-lubed and re-inserted for another similar cut. This happens dozens of times before we're close enough to slow the process down even more.


Photo 27 - Inserting the go gauge
Checking Depth
When the reamer has reached a depth that is close to final, but still some safe distance away, we screw the action back on, slip in a "go gauge", close the bolt and measure the shoulder gap as show in Photo 19 (Part 3).

 Photo 27 shows the receiver all the way against the barrel, but in order to close the bolt at this stage, it will have to be backed off a bit.

The go gauge is a steel duplicate of a minimum size cartridge without the neck area. The finished chamber should allow the bolt to close on the go gauge. A no-go gauge is the same thing, but 0.004" longer; the finished chamber should not allow the bolt to close on the no-go gauge.



Photo 28 - Reamer, PTG's Lambeth reamer micrometer and the reamer holder
Setting Up Final Cuts

With the shoulder gap measured with the feeler gauge, we know how much deeper the reamer needs to go in order to just barely let the bolt close on the go gauge. Now the trick is to bring the reamer in just that amount. John uses a micrometer type tool designed by Nat Lambeth and sold by Pacific Tool & Gauge which allows him to create a positive stop at the desired depth; that's what you've seen attached to the reamer in the previous photos.


Photo 29 - PTG reamer micrometer against the breech

Photo 29 shows the micrometer stop set right against the barrel, this would allow no further travel of the reamer. From there, it is backed off by the desired depth of the next cut. For instance, if we calculated that the reamer needs to go in 0.050" more, that might be divided into three or four more cuts, so the micrometer might be set to allow 0.020" travel on the next pass, then 0.015", then 0.010" then 0.005" - that's just an example, not necessarily the actual numbers used. The point is simply that you really sneak in on the last little bit and this tool allows you to do that with great precision and repeatability.




Photo 30 - John borescopes the chamber and throat
Final Chambering Steps
After each of these final stage cuts, the action is installed on the barrel and the shoulder gap measured. Once we hit the point where the bolt closed on the go gauge with the shoulder gap at zero, we inserted the no-go gauge and measured the shoulder gap; it was 0.004", as expected. Ultimately, the barrel will be torqued on to the receiver and there will be a bit more rotation than with the hand tightening used during the checking process. That rotation will reduce headspace a little bit and it is possible that the chamber would be a bit short. Therefore, at this point we made one last cut of 0.002" to allow for the additional barrel rotation on final installation while remaining within the allowable range. As it turned out, this was a great call, with fired brass being just where I wanted it and allowing easy resizing. John cleaned out the bore and borescoped it to make sure that the chamber and throat were free of scratches or burrs.


Photo 31 - Turning the shank to final diameter
Shank Diameter
With threading and chambering complete, the barrel was almost ready to come out of the lathe, however, one last operation remained on this end. That last step is to turn the shank down to match the old barrel to ensure that the barrel will remain free-floating in the stock. A few light passes of the cutting tool and some light polishing took care of that. Finally, all of the breech-end work was done; the barrel came out and was flipped end for end on the lathe with attention turning to the muzzle next.


Photo 32 - Ready to work on the muzzle end


The Voyeur's Guide to Barrel Chambering - Part 3

The Voyeur's Guide to Barrel Chambering - Part 3
by Germán A. Salazar and John Lowther



Photo 16 - John Lowther
 As we continue our series, the breech end of the barrel remains the focus of our attention. Now that we have a threaded, properly dimensioned and well centered tenon on the barrel, it's time to prepare the end of that tenon to mate with the bolt.

There are various breech face styles, varying by action manufacturer and sometimes by the rifle's intended purpose. The Remington style with a recessed face that envelopes the bolt nose is very common and it provides excellent gas handling and safety in the event of a case rupture. However, feeding is not as smooth as with a coned breech face such as the Springfield 1903 and the original Winchester Model 70 used. A few actions call for a flat breech face, the RPA Quadlock is one example of this.


This project involves a BAT 3 lug action with a coned breech face; accordingly, our next step is cutting the cone and finalizing the tenon length to properly fit this action.





Photo 17 - Cutter centered and ready

Cutting the coned breech face, like every other operation involves careful measurement and many small cuts until the final dimensions are reached. In Photo 17 we see the proper cutter, aligned with the bore, ready to begin.



Photo 18 - Cutting the cone


The first cut removes a tiny amount of metal near the bore. The next cut begins a little deeper and thus comes out a little further along the breech face.


Photo 18 shows the process after five or six passes. The cone angle is set by the angle of the cutter and remains fixed throughout the process.


There are coned reamers made now (think of a large deburring tool) but this is the old way and can be adapted to any cone angle. The BAT, for instance, calls for a 25 degree cone angle, whereas most other actions use a 30 degree cone.


Photo 19 - Measuring the shoulder gap
 Just as when we were establishing the basic length of the tenon earlier, the feeler gauges come back into play as we establish the final length of the tenon.


The tenon must be short enough to allow the receiver to screw on all the way without running into the locking lug abutments. However it must also be long enough to provide a close fit between the bolt nose and the cone, allowing just enough clearance to ensure proper functioning in all conditions (heat, cold, dust, etc.).


With the bolt in the receiver, the action is screwed on to the tenon until it stops. The resulting gap at the shoulder is measured and that amount of material is removed with additional passes on the cone. Eventually, the gap is zero and the shoulder comes into full contact.



Photo 20 - Finished and polished cone
  Of course, at that point, the bolt nose to cone clearance is also zero, so additional passes are made to push the cone deeper, creating the desired clearance. Too much clearance between the bolt nose and the cone is undesirable as it creates a larger rearward escape path for high pressure gas in the event of a case failure. Excessive clearance also increases the possibility of such failure by leaving more of the case hanging out of the back of the chamber without support. We settled on 0.015" as our nose-to-cone gap based on the very dusty conditions in which the rifle will be used.

The finished cone should be smooth for good feeding characteristics. A little polishing with fine grit paper may be necessary once the cutting is done. No need to make a mirror out of it, but it shouldn't catch your fingernail as you run across the surface.

Photo 21 - Visual check of bolt nose fit to the cone








Photo 22 - Front view of finished cone
 Photo 21 shows the nose of the bolt against the cone, this isn't part of the machining process, we're just admiring the matching angles. Photo 22 is just another view of the finished cone.
















Photo 23 - Action screwed onto the finished breech end of the barrel, but no chamber yet
 The final result is that the action screws on to the barrel and actually looks like it's ready to fire. Of course, we haven't cut a chamber yet, so appearances are indeed deceptive in this case. Tangible progress, nonetheless, and quite satisfying to reach this stage.


 Click here for Part 4




The Voyeur's Guide to Barrel Chambering - Part 2

The Voyeur's Guide to Barrel Chambering - Part 2
by Germán A. Salazar and John Lowther

As we take up the second installment of the series, our attention turns to threading that lovely barrel tenon that we cut in the previous installment. With the exception of some rimfire actions and perhaps an odd centerfire, basically all barrels are threaded into the receiver. The quality of threading has a significant effect on the ultimate accuracy potential of the rifle; the threads must be concentric to the bore and a good fit to the receiver's threads. The concentricity is taken care of by performing all machining operations on the breech end of the barrel without disturbing the original setup in which the bore was centered in the lathe.



Photo 9 - Cutting the relief groove on the tenon
Clean-up and Groove
The first step John performed was a clean-up cut across the breech face of the barrel. This removed the stampings and gave a clean working surface for some future operations.

The next step (Photo 9) was cutting the relief groove at the base of the tenon. The purpose of the groove is to give the machinist a little bit of breathing room as the lathe advances the thread cutting tool automatically but the machinist must manually stop the advance.

Without the groove, he has to pull the cutter out of engagement at the exact moment that it's about to crash into the shoulder (and break) on each of a dozen or more passes required to cut the threads to full depth. For this reason, some call the relief groove the "chicken groove" as it takes a mighty brave (and skilled) machinist to thread the tenon without one. The presence or absence of the relief groove does not affect accuracy.

The relief groove is cut with the tool angled slightly away from the shoulder to ensure that the shoulder surface isn't altered. If you look carefully, you'll see that the groove cut actually doesn't extend all the way to the shoulder surface.
 

Photo 10 - Squaring the thread cutting tool to the tenon
Threading Basics
At this point, the cutting tool used to cut the relief groove is removed from the tool post and a thread cutting tool is inserted. The thread cutter must be squared to the tenon as the tool post rotates and can bring a tool to bear at any angle. Photo 10 shows the use of a simple alignment tool to set up the cutter at a 90 degree angle to the tenon.

The cutter is for a 60 degree thread angle, standard for almost all receivers. Some older rifles such as the M1 Garand use a square thread, you can research thread types someday and entertain yourself. For our present purposes, we'll leave that topic aside.



Photo 11 - Applying machinist's blue to the tenon
The final step before we begin to cut the threads is applying a coat of machinist's blue to the tenon. This will allow us to make a very light initial pass with the cutter to ensure that the lathe is properly set to cut the desired thread pitch. In this case, for the BAT receiver, the correct pitch is 18 tpi (threads per inch). In the event that the lathe were improperly set, it could be re-set to the correct pitch and the threads cut with no interference from the initial super light pass.



Photo 12 - Slow but certain progress cutting the thread
Cutting and Checking the Thread
Once that first super light pass was made and the 18 tpi thread pitch confirmed, John began to make his actual cutting passes. Just like cutting the tenon itself, threading the tenon is slow and careful work with each pass removing only a tiny amount of steel.

The lathe picks up the thread at the same starting point on each pass and moves the cutter ahead automatically. The machinist watches his indicators, whether mechanical or digital, and pulls the tool away from the barrel when it reaches the end of the travel (either the groove or the shoulder as the case may be).




Photo 13 - Trial fitting the thread
Once the thread reaches a depth close to the the final, the trial fitting begins. If the thread depth is too shallow, the receiver won't screw on because the threads in the receiver can't engage those in the barrel. Slowly, over the course of several more passes, the fit goes from zero, to tight, to snug, to just right. This step calls for a great deal of care and a good touch by the machinist as it would be easy to gall the barrel thread and receiver thread during the trial fitting.




Photo 14 - Final thread fit to the receiver
Finishing Up
Eventually, the thread is cut deep enough and the tenon will screw into the receiver with the right feel (clearance). At this point you will probably discover that the tenon is a bit long and it runs into the locking lug abutment in the receiver before the barrel shoulder makes contact with the face of the receiver. A feeler gauge can be used to measure the gap between the shoulder and the receiver face, then that amount is machined from the back of the barrel. The goal is to achieve solid contact between the shoulder and the receiver without creating a big gap inside at the locking lug abutment.



Photo 15 - Final threading on the barrel tenon
So there you have it, a nice looking, good fitting thread on a tenon of the appropriate length for the receiver.

The slightly rough look of the threads in the picture is from the anti-sieze compound on them, the threads themselves are quite smooth.

Click here for Part 3

The Voyeur's Guide to Barrel Chambering - Part 1

The Voyeur's Guide to Barrel Chambering - Part 1
by Germán A. Salazar and John Lowther

A voyeur's guide to barrel chambering? Well, yes - this series isn't intended for anyone who owns a lathe; instead it is for those of us who send an action off to get a new barrel installed. Those who have the equipment know what to do and how to do it and I have nothing to teach them. On the other hand, if you've ever wondered just what goes into barrel fitting, this is it. We could have titled it: Everything You Always Wanted to Know About Barrel Chambering But Were Afraid to Ask - but that's kind of long for the index page.

The basic steps covered are threading, chambering and crowning the barrel blank. Each machinist who performs these operations has his preferences from among many possible ways to accomplish these tasks; what we'll show is John's way. If your man has a different approach, that's great, it's what works for him and this isn't intended to have you ask him to change his ways or to say that the way we show is the best or the only way; all it is, is one way - John's way.


Photo 1 - BAT action with new barrel blank (above) and old barrel (below)

John generously volunteered his time, effort and machinery for this series, and I must reiterate what we've mentioned before: John is not a professional gunsmith, he does this for his own entertainment and does not accept outside work. The division of labor for these articles is simple: John does all the hard work, I take pictures, type the text based on John's descriptions of each process and generally try to stay out of the way while the lathe is turning and the chips are flying. As always, just click on any picture to enlarge it for more detail.

The project at hand is a very typical one: install a new barrel chambered in .308 Winchester on a modern target action. In this case, the action is a BAT with a coned bolt face. The processes shown and described in the series are the same for just about any action, where details differ we will try to point that out.


Photo 2 - Breech end of new Krieger barrel blank

When you buy a barrel blank, there is quite a bit of information stamped on the breech end, let's take a look at it. First, the obvious manufacturer identification, this is a Krieger. At the top is the barrel's serial number, you'll need this if there is something wrong with the barrel, so write it down. Below you see the letters NF, I don't know what that is, maybe the machine operator's initials, but I'm just guessing. On the left you see the bore and groove dimensions, this one has a 0.300" bore diameter and a 0.308" groove diameter. These are standard dimensions for a .30 caliber barrel, but Krieger (and most manufacturers) offers some small variations on those dimensions. On the right is the all important rate of twist, in this case the 11 indicates that the rifling has a 1:11" rate of twist. Just below that, the SS confirms that the barrel is made of stainless steel as opposed to chrome moly (CM).


Photo 3 - Barrel in the lathe
The blank is inserted into the lathe with the breech end in the headstock and the muzzle end supported by the spider.


Photo 4 - Checking and minimizing runout at the muzzle end
The dial indicator on the muzzle end is used to watch the runout of the muzzle end of the barrel. Using the four adjustment screws in the spider (look at Photo 3, just over John's thumb) the muzzle end is centered up to minimize wobble. However, the real work of centering things up will take place on the breech end; this is just a preliminary operation.


Photo 5 - Indicating the breech end of the barrel
How much of the breech end to have sticking out of the headstock is determined by the length of the barrel tenon (the threaded part) as well as any amount you may want to cut off. The key is to keep the unsupported length of the barrel to a minimum, this will help the cutting tools work better.

The real work of indicating the barrel happens now. A long probe goes into the barrel, resting on the lands and grooves at least one inch in. The chuck is rotated by hand with an eye on the indicator. The chuck's jaws are adjusted to center the barrel perfectly in relation to the bore. This process can take quite a while, depending on the type of chuck used and the machinist's level of experience, but it is critical to a good final result. The reason that the probe is inserted at least one inch is to get it past the slight irregularities that exist right at the end of the bore. These are caused by the lapping tool reversing direction there during the barrel manufacturer's final lapping process.


Photo 6 - Measuring the thread diameter on the old barrel
If a barrel that was previously used on the rifle is available (and assuming it was done properly), it can be used to get a basic idea of the outside diameter of the threads. Although the final dimension will be based on trial fitting and a certain degree of feel (based on the machinist's experience) this can save a bit of time initially.





Photo 7 - First cutting pass begins
It's finally time to make some chips fly! With cutting oil on the barrel to keep everything cool and smooth, the cutting bit begins to bite into the barrel tenon.

The cutting tool removes a few thousandths of an inch of metal at most, so many passes are required to reduce the tenon diameter to the desired end size.



Photo 8 - Barrel tenon at final diameter before threading


After many passes of the cutting tool, the tenon is at the desired diameter and close to the final length. Reducing the diameter to 1.0605" from the original 1.250" took quite some time and effort.

This cut also establishes the barrel shoulder which will mate up to the receiver shoulder. All of the time and effort spent indicating the barrel to have the bore perfectly true to the headstock pays off here in producing a tenon that is parallel to the bore and a shoulder that is perpendicular to the bore.

Click here for Part 2
 

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