I know there is a topic about M855A1 in the terminal ballistics forum, but I felt it was appropriate to start a new thread.
First, did anyone read the article in the June edition of American Rifleman? It’s by Major John Plaster. The question I had regards his contention that a 1/9 twist is better for M855A1 rounds as opposed to a 1/7 twist. He quotes accuracy data. This sort of took me by surprise, given the length of the M855A1 bullet and its 62 grain weight. I realize 1/9 twist is better for 55 grain rounds, but I figured there wouldn’t be much difference for 62 grain rounds (as opposed to 75 and 77 grain rounds, where a 1/7 twist is necessary). Thoughts?
I’m glad he talked about the increased chamber pressures of the M855A1 round. I think we’re going to be seeing some premature bolt wear and port erosion with this round for certain (as the author mentions). Ultimately, we can thank the Clinton administration’s quest for a lead free round for all of this crap, but it’s a shame the Bush administration did nothing to stop it. I think the Mk318 is a better choice for a barrier blind round no doubt, but it’s not like troops can pick between the Mk318 and Mk262 for whatever mission they go on.
All of the above would be fixed by a 6.8 SPC chambered rifle of course, or issuing more SCAR-Hs
I believe the article says that the M856 tracer required the 1/7 twist to be stabilized, and that M855 was GTG with 1/9, which is also what I had always heard previously. I was shocked at the margin of greater accuracy 1/9 vs. 1/7, with M855, he stated he found in his testing.
Interesting to see the RETARDATION that went into this Goat Rope cartridge. Increasing the pressure to get this stupid round where they want is about as dumb as it gets.
Also interesting to see how the 1/7 hurt the accuracy of the SS109 bullet.
Agreed. It is beyond belief that our military would spend that much $ to develop ammo that operates at that high pressure, will break bolts, and will render ACOGs ineffective at longer ranges. Great job.
I wonder why would anyone want to increase the already too high chamber and port pressure in the M4, for a marginal gain in performance.
The improvement of the M885A1 over M855 is that you have a much larger and better steel penetrator, AND a reliably fragmenting bullet with no angle of attack issues and less dependant on impact velocity. All this without using an open tip, exposed lead, or an expanding design, so still complies with the letter of Hague.I guess designating a bullet “match grade” doesn’t hurt, either, no matter what is the reality. The bullet performance would be pretty much the same at slightly lower velocities (remember, the chamber pressure increases exponentially compared to muzzle pressure).
I think the idiots wanted the trajectory to match M855 as closely as possible. We run ACOGs all the time with everything from 55s to 77s and adjust on the fly. I’d rather have a reasonable pressure round and adjust my COG hold accordingly. Tying the ACOG’s reticle to the poor performing M855 was the first mistake. Just dumb on top of dumb.
Regardless of who was in control of the legislature when, etc… we know where this retarded nonsense is rooted.
The most perplexing thing is that this M55A1 load has a bullet which most likely has a slightly higher BC than M855, so lowering the muzzle velocity (which is also higher in the M855A1) would actually make the two trajectories more similar.
The flyers mentioned in the article are likely due to the complex construction (leading to offset axial center of balance), and the probably the jacket crimps with some variability onto the steel nose, that’s why some presentations say that it is OK if some nose movement is noticed.
We only had several hundreds of millions of rounds carried in magazines and ASPs both theaters and several tens of billions of rounds in the war stocks at the time.
Yeah… I understand that. I guess the idea that M855 ever made it as the standard load is frustrating. I have and old magazine with an article just like this one… but on the subject of going from M193 to M855.
An OTM is the right answer. The specialized units have figured this out. This M855a1 projectile has some positives however.
I though that extremely long .224 bullets like 75-77gr. match bullets and these 62gr steel core bullets would fail to stabilize adequately in anything less than a 1:7 or 1:8 twist barrel?
They made the M855A1 bullet even longer, and it’s somehow OK (or even better) in a 1:9 barrel?
Back in the day, the swiss did their tests and chose a 1-10" twist for their Sig 556 because of better accuracy. They do have a proprietary 5.56 (63 gr lead core, non fragmenting) load, but I’ve read a chilean paper (their state factory, FAMAE, builds the Sig 550/556) where they tested true M855/SS109 and got best accuracy out of 1-9 or 1-10 barrels. I’ve shot pulled M855/SS109 bullets in 1-10 barrels and they do group very well, so it is no surprise that M855A1 groups well in 1-9 barrels.
Wow. For years I’ve been drinking the M4C.net kool-aide and thinking that anything less than a 1:7 twist was inadequate… now it turns out that 1:9 or 1:10 is just fine?!
