Range Report M1A and 155 A-Maxes

[Grump]

Tried some 4064 in and OCW test and the promising results were at speeds we're not supposed to see with a 22-inch barrel.

FA 63 Match cases, reloaded 1x before
WLR primers
Seated 2.82 or so OAL
New ordinary match barrel from Springfield Armory
Temp 80 F, humidity probably 30-40.

45.0 (last of the 3 sighters, started at 43.4 and didn't get speeds)
2893.1

Shots were fired round-robin style.

45.3--2898.6, first two shots touching, 3rd an inch away at 11:30

45.6--2890.7, first two shots touching, 3rd 1-3/8 inch away at 10:00

46.0--2912.6, first two shots same hole, 3rd 1-3/8-inch away at 11:30

46.3--2926.9, first shot in the same spot as the first two in the prior three loads' groups, 2nd an inch away at 10:30, 3rd another half-inch above the 2nd

46.6--2959.8, first two shots almost touching, a half-inch left of the rest of the earlier groups' first shots, 3rd shot 7/8-inch away at 11:00.

With the earlier barrel, the rifle tended to shift POA up about 1 MOA after firing 8-12 shots in a string. Perhaps this is also at play.

But since I expected safe velocities to top out at about 2880 or so from a 22-inch, I'm going back for a re-test with 45.6 as the top charge. Faint prints of the line on the bolt where the extractor sits were visible starting at 45.6, and ejector wipe started showing up at 46, so I'm not going to chase the accuracy even at 45.6. I'm not even sure about accepting 45.3 unless I get QuickLoad and the pressure estimate if good for these cases (water capacity 55 grains).

Some of these groups are at 1 MOA with the last shot included, with horizontals between 1/2 and 3/4 (only 1 had horizontal of 1.1 inch). That may be the limit of the barrel, but if it has a POI shift that's predictable in both onset and distance, I can keep shots at 3/4 MOA or significantly less.

I hope.

 

[Greg Langelius *]

Re: M1A and 155 A-Maxes

One of the things to heed when doing round robin shooting with the M1A is the gas cylinder plug. It is intended to be tightened only enough that it still loosens up every 60-100 rounds. Any tighter is overtightening and can result in stripped gas cylinder and/or plug threads. Expensive and a terminal casualty right then and there until replacements can be scrounged, which can take a long, long time. Conversely, if the plug loosens enough to leak, groups go to hell; so you need to check it about every 50 shots or so.

Greg

 

[mgd45]

Re: M1A and 155 A-Maxes

Mine seems to loosen up after about 10 rounds.....i guess I need to tighten it down with something....

 

[Grump]

Re: M1A and 155 A-Maxes

Well, Springfield Armory tightened the gas nut hard enough that it's still in place without being loose after more than 100 rounds.

The gas cylinder is very, very hard stainless. The surface hardening on the nut is about equal to the carburized "shell" on a USGI receiver.

I'm not worried about stripping. I do check the nut every 100-300 rounds just like I check the gas cylinder for free movement and the scope mount screws if that's mounted at the time.

 

[Grump]

Re: M1A and 155 A-Maxes

Followed up with the more promising 4064s, as well as a run of Varget.

Temp 88-92 F

44.7 gr (fired 3 round-robin)
2898.5 only one reading.

45.0 gr (fired 3 round-robin, then a 5-rd group)
2925.8, bogus reading, 2931.8. Tiny-sample avg. 2928.8

45.3 gr (fired 3 round-robin)
2934.7, two bogus readings

The 5-rd group was .975 CTC, despite about a 1/2-inch wobble area and two shots called at the left edge of that wobble. Four of those five were about .625. Attention to cheekweld and a really tall comb "extension" helped a lot.

Varget

44.0
2768.1, 2791.9, 2800.4. tiny-sample avg. 2786.8

44.4
2793.9, 2808.3, bogus reading. Avg. 2801.1

44.8
2817.5, two bogus readings

45.2
2830.1, 2845.6, bogus reading. Avg. 2837.85

45.6
2874.9, 2851.8, bogus reading. Avg. 2863.35

My older PACT Timer/Chrono seems to drain each 9V battery in less than 2 hours of operation. I'm going to run some math on the funny readings to see whether the malf is from losing track of the screen spacing... Bought the thing used and kinda got ripped cause it's the older version and cannot be upgraded. PACT doesn't seem very interested in keeping its customers happy, either.