Stupid question of the week: is M855 safe in ARs?

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http://www.inetres.com/gp/military/infantry/rifle/556mm_ammo.html

According to this, M193 chamber pressure is 52,000 psi, and m855 is 55,000. I assume any quality AR can handle the pressure.

They also say:
This ammunition should not be used in the M16A1 except under emergency conditions, and only at targets less than 90 meters in distance. (The twist of the M16A1 rifling is not sufficient to stabilize the longer projectile of the round).
Click to expand...

I assume a Colt SP1 has the slower twist... and I shouldn't shoot m855 through mine?



STUPID QUESTION #2:

Cartridge, 5.56mm, Ball, M855, Lead Free

The M855 "lead free" ball cartridge has a bullet with a conical steel insert and a tungsten composite core in a copper alloy jacket. The intended use is to maintain environmentally "clean" ranges.

The cartridge is identified by a green bullet tip.
Click to expand...

How do you tell the difference between the 2 types of M855 green tip? Cut one in half? :confused:
 
You are not likely to encounter M855 lead free on the civilian market.

M855 is safe in any AR that has a 5.56mm NATO chamber rather than a .223 Remington chamber. Your AR should be marked but the markings can be wrong. Search on this topic, many threads.

M855 will stabilize if you have a 1:9 or faster twist barrel. In a slower twist barrel (1:10, 1:12, 1:14) it is safe to use, assuming a 5.56mm NATO chamber, but likely will not stabilize.
 
I assume any quality AR can handle the pressure.
Click to expand...
They were made for use in the M16, so it is safe to assume any AR-15 with a 5.56 NATO chamber is safe with them.

All Colt SP-1's had 1/12 rifling and will not stabilize the M855 very well, if at all.

I don't know how you tell the differance but cutting one in half should work.

rc
 
The barrel marking will almost always be more definitive than a reciever marking regarding what kind of chamber and twist specs you have. (Obviously if it was a rifle assembled outside a factory, it is the only marking that matters at all.)

If it is marked 5.56, and with a twist of 1:9 or faster, I would not hesitate at all to shoot M855 spec ammo in it.
 
If it is marked 5.56, and with a twist of 1:9 or faster, I would not hesitate at all to shoot M855 spec ammo in it.
Click to expand...

Generally agree but some manufacturers have been known to mark barrels as 5.56 when they actually have a .223 chamber. You'd have to do a search for details. I don't think Colt has been known to do such a thing but I'm not positive.
 
Colt SP-1's were all .5.56 NATO.

They never made an AR that wasn't except for the stainless steel barreled match guns in .223. They will be so marked on the lower barrel I think.

rc
 
As others have mentioned, it is fine for any 5.56NATO rifle. It should shoot fine in any twist (with the possible exception of 1 in 14") as long as you don't use tracers (which are longer and require a faster twist to compensate). :)
 
I disagree.
M855 are both partial steel core & boat-tail, and are much longer then 60 grain flat base spitzers.

A 20" SP-1 rifle with 1/12 would be marginal at best with them.
A 16" SP-1 carbine with 1/12 probably would not stabilize them.

rc
 
Absolutely DO NOT shoot the M855 through an AR15. This military ammo and will destroy your rifle.

Send it to me (PM for shipping address) and I will shoot it through my M4 and let you know how it was.

Cameron
 
Perfectly safe to use in your AR15, but depending on your twist rate, it may not shoot very accurately. As long as your twist rate is faster than 1/12 you shouldn't have any problems.
 
Generally agree but some manufacturers have been known to mark barrels as 5.56 when they actually have a .223 chamber.
Click to expand...

Armalite has in the past. Don't know if that's still the practice.
 
Some manufacturers mark .223 when it is in fact a Wylde chambering or 5.56. (liability issues). Rock River and Ruger Mini-14 use Wylde I believe. I have Bushmaster barrels marked .223. Don't remember the others...
 
Colt SP-1's were marked .223 on the lower receiver, but are in fact 5.56 NATO chambered. Ruger Mini-14's of the day were the same.

They were made back in the day before there was all the SAAMI fooforall about the difference.

Back then, there was only the M193 55 grain FMJ-BT GI load, and they were perfectly safe in either chamber.

The only problem I ever heard of back then was some SAKO Vixen .223 Rem rifles that got made with .223" barrels instead of .224" barrels.
And some Remington 40X match rifles with very tight .223 match chambers & barrels.

They both would sometimes blow primers with GI ammo.

I am still of the openion that much has been made about nothing when it comes to normal .223 chambers and normal 5.56 ammo being dangerous.
It may be dangerous with the longer GI tracer ammo but I have never shot any of it in a .223 so don't know.

rc
 
Rock River and Ruger Mini-14 use Wylde I believe.
Click to expand...
I think currently, RRA offers true 5.56x45, .223, or Wylde (your choice), but 5.56 marked guns are true 5.56 chambers, as I understand it. Not sure what they've done in the past, though.
 
It may be dangerous with the longer GI tracer ammo but I have never shot any of it in a .223 so don't know.
Click to expand...
I don't believe that it poses any danger, only unlikely to stabilize due to the additional length.

:)
 
I believe RC was talking about shooting 5.56 tracer (longer bullet) in a true .223 chamber.

the OCL is still the same, though, right? They just seat it deeper in the case IIRC.
 
I believe RC was talking about shooting 5.56 tracer (longer bullet) in a true .223 chamber.
Click to expand...
In that case it may be a concern, but I wouldn't think it would be any different from any other 5.56.

the OCL is still the same, though, right? They just seat it deeper in the case IIRC.
Click to expand...
Correct, it is still within OAL specs., so very little if any change in cartridge length.

:)
 
I think currently, RRA offers true 5.56x45, .223, or Wylde (your choice), but 5.56 marked guns are true 5.56 chambers, as I understand it. Not sure what they've done in the past, though.
Click to expand...

I'll have to look into it, but just because it's stamped "5.56mm" on the bbl doesn't make it so.

I don't think it's so much of a "dangerous" condition as it is, however, a reliability issue.
 
RRA is indeed putting out 5.56 barrels, along with .223 Wylde for their match or varminters (I think all of the SS barrels).
 
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