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!

 

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