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Thread: M855A1 accuracy test.
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1 November 2016, 17:07 #1Senior Member
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M855A1 accuracy test.
This rifle normally shoots 1.5-1.8MOA with Barnes and Gold Dot. This is not the best, nor the worst group of the day, but it is the group that I felt I did my part on the best. Every shot I called as "on". This was all gun/ammo. performance is slightly worse than the MK318 SOST (2.5moa or so on average) that I have, and slightly better than M855 that I typically shoot. The action cycled with authority, but nothing that concerned me. It felt like good, stout 5.56. The brass cases showed slight smearing just like hot M193. The steel backers at the public range were completely un-damaged (but have some gold colored smears on them now), but are also at like a 10-20* angle.
*100 yards.Last edited by JGifford; 1 November 2016 at 17:14.
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1 November 2016, 17:55 #2
... the real question is, where did you get 855A1? Granted I haven't looked in a while, but last I checked I could only find it on GB; and you know how those prices work.
It's an interesting round I will say. From talking with someone in SF, he told me that their M4's did not like it at all. I don't remember the specifics anymore, but I do recall him saying that extended use of the round caused the barrel to wear out fast.
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1 November 2016, 19:55 #3
It's pretty hot velocity-wise, at least in the batches I have. The tips also increase wear on the feed ramps in the upper receiver, which is why they had to come out with a new revision to change the feed angle so the tips hit the barrel extension instead. You should only use pmags with m855a1 (or other magazines that have the same feed angle).
Will - Owner of Arisaka LLC - http://www.arisakadefense.com
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1 November 2016, 20:43 #4Senior Member
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1 November 2016, 21:46 #5Senior Member
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2 November 2016, 05:33 #6
Here's a cross section of the "old" M855A1 on the left and the "new" one on the right
From the webs about wear on rifles:
"Since its introduction, the M855A1 has been criticized for its propellant causing increased fouling of the gun barrel. Post-combat surveys have reported no issues with the EPR in combat. A series of tests found no significant difference in fouling between the old M855 and the M855A1. However, manufacturers have reported "severe degradation" to barrels of their rifles using the M855A1 in tests. The Army attributes pressure and wear issues with the M855A1 to problems with the primer, which they claim to have addressed with a newly designed primer. It uses a modified four-pronged primer anvil for more reliable powder ignition, with a stab crimp rather than a circumferential crimp to better withstand the new load’s higher chamber pressure, increased from 55,000 psi (379.2 MPa) to 62,000 psi (427.5 MPa). During Army carbine testing, the round caused "accelerated bolt wear" from higher chamber pressure and increased bore temperatures. Special Operator testing saw cracks appear on locking lugs and bolts at cam pin holes on average at 6,000 rounds, but sometimes as few as 3,000 rounds during intense automatic firing. Firing several thousand rounds with such high chamber pressures can lead to degraded accuracy over time as parts wear out; these effects can be mitigated through a round counter to keep track of part service life. Weapons with barrel lengths shorter than the M4 firing the M855A1 also experience 50 percent higher pressures than a full-length M16 rifle barrel, which can cause port erosion that can boost the automatic fire rate, increasing the likelihood of jams"
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2 November 2016, 05:39 #7Senior Member
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2 November 2016, 05:40 #8Senior Member
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Accuracy testing will be repeated today in good light. I was seeing a lot of variation between groups, and I think I was to blame, as I had slept very little and it was getting dark. I called every shoot "good" on that last group, but I shot it technically past sundown. I am going to fire another 3-4 groups today, and average them, to present a more accurate depiction of what one can expect from current M855A1.
Fouling yesterday was nothing special.
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2 November 2016, 06:39 #9
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2 November 2016, 08:16 #10Senior Member
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2 November 2016, 17:32 #11Senior Member
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Averaging a total of (9) 10 shot groups fired over the span of 2 days, I arrived at 3.59 MOA.
The best group measured 2.07 MOA
The worst group measured 4.707 MOA.
Interestingly, the first groups of the day which were fired with M855A1 (which would be the second total group fired, on Day 1, so NOT the first group total, fired of any day), showed the best precision on both days.
I followed my typical procedure as regards to loading, resting the rifle, and barrel-heat (I let mirage off the suppressor be my quide) as to which I have followed in the past, which has typically produced 1.5-2.0MOA from ammo the rifle likes.