Cartridges: .308 Palma Preparation and Loading

.308 Palma Preparation and Loading
by Germán A. Salazar

As the calendar tuns to October and summer begins to wind down in Phoenix, two things happen: first, we optimistically watch the weather report to see when the first day with a high temperature under 100 will arrive; and second, we turn our attention to Palma shooting.  Because the Highpower range at the Ben Avery Shooting Facility doesn't have covered firing lines, it falls out of use from late April to late October as the heat would make shooting there physically hazardous.  Instead, we spend the warmer months shooting 500 yard matches on the shaded firing lines of the Phoenix Rod & Gun Club and the Rio Salado Sportsman's Club.  But now, as the long-range season approaches, things get more serious.  The Arizona Palma State Championship is held on the first weekend in December, relatively early in the season, so anyone with a new Palma rifle or loads has to work quickly to get them sorted out.  Naturally there are many who have shot long-range over the summer in other locations, but for the majority of us that isn't the reality so the earliest part of the season is a hectic scramble to get ready for the big match.

The New Rifle
During the summer, my new Palma rifle was completed; it is built around a Borden Tubegun Special action.  Clark Fay chambered a 30" long Krieger 1:11" twist heavy Palma barrel for it and Jim Cobb glued the action into an Eliseo R1 long action stock.  With all the parts in hand, I assembled it with a Doan Trevor walnut grip and an X-Treme Shooting two-stage trigger.  A Warner rear sight and a Riles front sight round out the hardware.  However, I may switch the front sight to a Centra Goliath soon, that's at the top of my list of things to evaluate on the range as soon as possible.

I had the new rifle built to match my .30-06 tubegun that I have enjoyed shooting so much.  In fact, apart from the serial number on the action and the barrel contour, there isn't much to distinguish one from the other.  Although I like the 28" MTU profile on the .30-06, I opted for a 30" heavy Palma contour on the .308 for a couple of reasons.  First, the little .308 can always use those extra two inches (5 cm) for a slightly higher MV when shooting at 1000 yards.  Second, because of that extra barrel length, I felt that the slightly lighter heavy Palma profile would yield a balance similar to the shorter MTU profile barrel on the .30-06.  As things turned out, that was a good estimate and the two rifles have very similar balance and feel.  Stock adjustment largely followed the guidelines from my article on that topic and, in fact, ended up idential to those on the .30-06 tubegun. 

The barrel was chambered with a reamer on which Clark and I collaborated.  It has a 0.336" neck diameter and a 0.114" freebore length, the rest of the dimensions are fairly standard.  These dimensions were specified with Winchester brass and heavy bullets in mind.  A Sierra 190 MatchKing will have the base of the shank even with the base of the neck when the ogive is at the lands and a 175 Berger will have the base of the shank about halfway up the neck when its ogive is touching the lands.  Other bullets in that weight range will fall somewhere in between those two, but since the Sierra 190 and the Berger 175 are my principal choices for Palma shooting, they are the ones on which we focused.

Although most Winchester brass could be used in this chamber without neck turning, it is my practice to turn necks on all of my brass.  I turn the necks to 0.0125" thickness which yields a loaded round neck diameter of 0.333" thus giving the cartridge 0.003" diametrical clearance in the chamber - not much, but enough to ensure safety since each case neck is identical.  Any time a chamber such as this one, with a neck diameter under SAAMI standards is used, all brass should be checked before use and the reloader should have a very thorough understanding of the clearances sought and the means to achieve them.  This is a significant safety concern and should not be taken lightly.

Early Testing at 500 Yards
Once the rifle was put together, I shot it in a few matches at 500 yards to evaluate loads and refine the stock and trigger adjustments.  During the summer, we shoot 500 yard matches every available weekend day, so testing is simply done in the matches.  Between work and home responsibilities, there's really no free time to go to the range for testing outside of the match schedule and, of course, I prefer to shoot the .30-06 so the .308 testing got squeezed in but didn't become my sole focus at that point.  The following account of this testing may seem a bit tedious, but that's how it really goes.  I hope that it gives an insight into the process I follow to identify good loads and eliminate those that just won't do the job.

The first test (July 24) was with the Sierra 155 MatchKing (2155) and H4895; this is a standard load for me and I expect any good Palma rifle to shoot it well.  Although the barrel is optimized for heavier bullets, it shot the155's perfectly and that first day at 500 yards resulted in scores of 199-16X and 200-14X.  The trigger adjustment needed more refinement, so I finished that match shooting the .30-06 in the third string for a total of 598-38X to win the match. 

I look at several things in judging a load: score, X-count and place in the match.  The score is the least important of these because a 9 is more often a result of shooter error than of the load.  The X-count is a very useful measure of a load's performance and the placement in the match results is a reasonable indicator of overall shooter performance, especially when conditions are challenging.  This holds true as long as the club has a good group of shooters of equal skill, which is certainly the case in this area where no win comes cheap.

The next day, July 25, I shot the rifle again, this time with the 175 Berger and H4895 (200-14X), then with the Sierra 190 and IMR 4064 (199-12X) and finally with the Lapua D46 185 gr. and IMR 4064 (199-09X) for a total of 598-33 and another win.  I was pleased with the performance of the Berger 175 and the Sierra 190 and decided not to pursue the D46 any further as it was clearly not shooting as well as the others. 

The August 8 match resulted in a disappointing second place 594-21X on a very windy day; Doug Frerichs won with a 594-29X shooting his 6.5-284.  I was shooting the Berger 175 (198-07X, 197-05X, 199-09X); was I just "off" that day, was it the load, was it the rifle?  Although the wind seemed the most likely factor, I left the range with some doubts and decided to chronograph some loads before going further.

Chronograph Testing
On August 21, I was able to get to the range for a chrono session and tested a few loads.  The high temperature that day was 106 degrees and it was right at 100 during the session.  I chronographed three combinations that were of interest: the Berger 175 with H4895, the Sierra 190 with IMR 4064 and the Berger 190 VLD with VihtaVuori N550.  The first two are what I've been shooting in my other Palma rifle which has an identical barrel and chamber and the last combination is one that I hoped would provide a material improvement in wind drift and retained velocity for 1000 yards.

The Berger 175 with H4895 testing showed 2830 fps and an SD of 5, clearly good numbers for this bullet and comparable to the load I was shooting in the other rifle.  The last two Palma matches I shot with this load (February 4 and 5, 2010) gave scores of 448-27X and 448-26X, it's a good load.

The Sierra 190 with IMR 4064 test ended at 2660 fps with an SD of 13.  This load has been excellent at 800 and 900 yards in the other rifle, often producing high X-count clean scores, but has usually had a low X-count at 1000 yards.

Finally I got to what I hoped would be the most interesting combination: the Berger 190 VLD and N550.  I worked the load up carefully, first in 0.5 gr. increments, then smaller as I neared the maximum charges shown in the manuals.  My final load showed 2770 fps with an SD of 8 - very promising!  The only flaw in the plan is the total disappearance of N550 from dealer stocks in the US and my meager supply of 3 lb. of the magic powder.  But a promising load nonetheless.

Back to the Range
The day after the chrono session (August 22) I shot three loads in a match.  First up was the 190 VLD, N550 load which resulted in a 199-12X, that didn't seem too bad.  Next, I shot the standard Sierra 190, IMR 4064 load and fired a 200-16X that was so much tighter than the first load that it was clear to me that without further development on target, the N550 load wasn't going to cut it and I don't have enough powder to develop it at this time.  More's the pity, because it truly does look promising for 1000 yards.  Finally, I shot the Berger 175 H4895 load, but in the Lapua small primer case as a final test of that case.  The score of 199-11X was not consistent with the mild conditions we had; my target puller, John Lowther, commented that the group really opened up and the elevation spread doubled.  I'm done experimenting with that case as well.

The Sierra 190 load shot so well that I decided to pursue it a bit more, bumping the powder charge a bit to see if it would still shoot well and perhaps then see if the 1000 yard performance increased when we begin shooting long-range again.  Unfortunately, as things worked out, match day (September 4) was very windy and comparisons of small changes in the load were impossible to see.  I shot 196-10X, 200-09X (+0.5 gr.) and 198-04X (+0.8 gr.) for a 594-23X, which although low, was enough to win on that day.  I'm still uncertain of this load's potential, or even whether I'll keep working with it.  It shoots great from 500 to 900 yards but just doesn't shine at 1000.

The final test day came on September 11 and I was back to the Berger 175, H4895, WCC 60 brass and PMC (Russian) primers.  The day was a rare one for Phoenix, a forecast high of only 100 degrees and almost no wind.  If the load was going to shine, this was the day.  The three strings were loaded identically except for seating depth.  The first string had the bullets seated for a jump to the lands of 0.010" and I shot a 200-11X - not too exciting given the conditions.  I wondered if my shooting was "on".  The next string, with the bullets seated to a jam into the lands of 0.010" worked a little better, with a score of 200-15X and noticeably tighter elevation spread.  Now things were getting interesting. 

The last string was seated to a jam of 0.020" and conditions remained favorable, about 1.5 to 2 moa of wind.  With 14 shots on paper, I had a 140-13X going when the wind picked up significantly so I decided to wait.  After a couple of minutes, I got nervous about the round in the chamber heating up (foolish thought) and opened the bolt.  Disaster struck, the bullet stayed in the barrel and powder spilled out all over the action!  A few minutes of very hectic cleanup, getting the powder out of the locking lug recesses, off the bolt lugs, and everywhere else, as well as knocking the bullet out with a cleaning rod, got the rifle back in operation.  Naturally, the wind hadn't been waiting for me and it had now reversed direction!  A deep breath, a quick prayer, a reasonable sight adjustment and a careful squeeze of the trigger got me into the 10 ring -whew!  A few more 10's and X's and the string finished at 200-16X for a match winning 600-42X, my 21st 600.  A fine end to the day and closer to a decision on loads.

Doing the Math
The ballistic challenge of a Palma match is the 1000 yard stage.  That's where the rubber meets the road and the load either works or it will cost you the match.  Somewhere between 901 yards and 999 yards, a bullet fired from a .308 runs into a wall, and that wall is the transonic region which roughly begins as the bullet's velocity drops to 1.2 mach.  Ideally, we can remain over 1.3 mach and avoid problems, but that's not always possible within safe pressure limits.

I use the JBM Ballistics program for all my calculations, it's accurate and always accessible online.  Running the numbers on the three final loads from the chronograph session plus my normal load with the Berger 155.5 produced some interesting data.  There's a lot more to evaluating ballistic data than just wind drift figures; and of course, the ultimate test is putting holes in paper at 1000 yards.  Nonetheless, the data provides some useful guidance.

Numerically, the 190 VLD at 2770 outshines the others by a good margin.  The drift is less, the retained velocity is higher and it is therefore, above the transonic region by a more comfortable margin.  Sadly, without additional load development to find the a bit more accuracy, I'm unwilling to shoot it at 1000 yards and since there is no powder with which to do that load development, the whole thing is shelved.  I could shoot the 190 VLD with another powder, obviously, but my supply is limited so I'll hold on to them until I find some N550 with which to experiment.

Looking at the Sierra 190's low retained velocity, well into the transonic region, I can see why it has never been a top performer at 1000 yards.  At 900 yards, it is still holding on to 1.281 mach, but it just plunges from there and the scores show it.  Although the wind drift figures are the same as for the Berger 155.5 at 2970, the accuracy just isn't there.  This load is at the pressure limit for the powder used (IMR 4064) and I don't have any good alternatives pending the arrival of more N550.  I realize that a lot of people like Varget for this application, but I am not satisfied with the lot-to-lot variability of Varget and I haven't done any pressure testing with Varget and the 190 so I won't simply jump into load testing with it.

At this point we're left with the Berger 175, which not only has good numbers in all categories, but is very accurate as shown in the mid-range testing and previous Palma scores with the other rifle.  You might ask why I don't go with the Berger 155.5, that is simply because the higher MV required by that weight class of bullet increases the possibility of bullet failure and a lost match.  The chances are small, but I have experienced it and don't care for a repeat occurrence.  Wind drift differences are minimal, especially when reduced to the difference in a 2 mph change which is as large as might occur without the shooter noticing.  The best reason for using the 175 is not reducing drift so much as it is reducing risk.  Additionally, the 175 load generates slightly lower chamber pressure than my 155 load and I like having that extra bit of safety margin.

Click here for Part 2 of this series:   Loading the .308 for Palma Matches

Related Articles
Palma Shooting in the US
Western Shooters' Pet Loads for Long-Range
Palma Bullets and Barrels
History of the Palma Match
Adjusting the Tubegun Stock

All contents Copyright 2012 The Rifleman's Journal