Using M855 Green Tip in 1/7 Twist Colt AR

No drawbacks. In fact it may well shoot better.

It should shoot better as that twist rate works better with longer bullets like the M855. Barrel life should be better with the heavier slower bullets as well. I wouldn’t expect a huge difference in barrel life as 556 tends to burn the throat of a barrel out much faster than a larger bore rifle.

BSW

That SS109 is exactly what that rifle is meant to fire. Same twist rate and round as what was standard issue since the late 80's, although it is being phased out now. That said, be advised that SS109/M855 is very inconsistent.

The military went to 1:7 twist specifically for the M855 "Green Tip" and its associated M856 tracer round. The M855 has a steel penetration over a lead core. The complexity of the design makes it marginally less accurate and consistent in performance than the more basic M193, but it is still plenty effective within its range, and better at penetrating some things. On that note, some ranges don't like it, because they feel it can damage their plates. I shoot a lot of M855 though with no complaints. It is accurate and effective enough for my uses. For everything else, I run 62 GR Barnes TSX.

The regular M855 shouldn't have increased wear on your rifle, but the newer M855A1 is loaded hotter and has a reputation for chewing up feed ramps.

jmr40 said:

No drawbacks. In fact it may well shoot better.

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My AR shoots the M855 better than the M193

Accuracy difference isn't huge in my Colt 6960, but I do notice that M855 tends to be a bit less consistent in its accuracy. Some of it seems to shoot about the same as M193, some of it shoots maybe a MOA more. Either way, it can be hard to tell the difference in a lot of the shooting I do, with the red dot, and the rate of fire I try to maintain with the AR. I buy the M855 as much for the ammo cans and the fact it comes on stripper clips, and the fact I like rounds like the 62 gr TSX, the Federal FBIT3, Speer 64 gr Gold Dot, and Federal Fusion MSR for defense.

MTMilitiaman said:

I buy the M855 as much for the ammo cans and the fact it comes on stripper clips

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Same here, although once in a while Federal will package M193 in that 420rd can on strippers, too. It's not the best bargain, but I get it when I need to reload my stash of strippers and sleeves.

I've found M855 to be about as accurate as M193 in my AR carbines, no more, no less. The only caveat to that is my Colt H-Bar, which detests anything 55grn, and lets you know it in pretty short order. Briansmith is correct... the chamber and throat will degrade, most likely, before the rifling does... particularly if you are doing rapid fire strings.

Ive never found M855 to be as accurate as M193 in my rifles. Not saying it's bad or anything but M193 always had a slight edge on accuracy. Top off that M193 tends to be a bit cheaper, I never buy M855 anymore.

But dont take that as me telling you not to buy M855. It's a good round.

I never got the appeal of M855 to be honest. It's more expensive than FMJ, it's usually a little less accurate than FMJ, and the penetrator doesn't do anything for civilians (and even the military doesn't like it any more).

In the grand scheme of things M193 vs M855 isn't a big deal, but I don't buy the green tips.

As others have said, it's absolutely fine for your 6920, in fact the Colt M4s were designed to shoot it.

According to the Internet and even comments on this thread M855 should be more accurate than M193 in a 16” 1 in 7” barrel but the opposite is the case with this particular gun.

This gun is very accurate with PMC .223 55 gr. FMJ. No I didn’t type that wrong. It loves PMC .223 even though it has a 5.56 chamber.

I have found Federal M855 to be inconsistent in both my 5.56 and .223 Wylde AR’s. It acts like it wants to give me a good group then it starts throwing flyers. I plan on getting some 62 gr. FMJ (without the steel core) to see how it performs in both guns.

It just goes to show that every gun is a separate rule onto itself.

I recently bought some 62grn BTHP component bullets to try out... if the 1:7 rifling is supposed to be better with longer/heavier bullets, I might as well see if I can get better accuracy if I'm going to go through all the trouble to prep brass and handload.

C-grunt said:

Ive never found M855 to be as accurate as M193 in my rifles. Not saying it's bad or anything but M193 always had a slight edge on accuracy. Top off that M193 tends to be a bit cheaper, I never buy M855 anymore.

But dont take that as me telling you not to buy M855. It's a good round.

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I have a few ARs, two prefer M193 to 855 and one that is more accurate with 855. My father and I had a bolt action 30-06; as he passed away, I have both and each still prefers a different load. Neither is a picky eater; that being said each is more accurate with the load they prefer.

IMO, ARs or whatever are no different.

I shoot M193 and M855 through my PSA build AR regularly. Accuracy wise, very little difference. I can find more difference in my shooting if I had caffeine that morning or not compared to 855 vs 193. As far as your rifle is concerned, it was designed with M855 in mind.