SAAMI .223 Chamber vs. Mil-Spec .223 chamber

B

Bartholomew Roberts

Moderator
A few questions for the knowledgeable people out there:

While surfing the net looking for commentary on the Spanish SS109, I found this little tidbit at http://www.ak-47.net/ammo/ss109.txt

Paramilitary 5.56mm ammunition should not be fired in commercial rifles with chambers reamed to SAAMI specifications. The SAAMI chamber used in sporting firearms has a smaller diameter bullet seat, a shorter throat and less free bore than military chambers. Chamber pressures can rise
dramatically when military ammunition is fired in them.

SAAMI specifications for commercial .223 ammunition specify an average chamber pressure of 52,000 CUP. When military ammunition is fired in the SAAMI chamber, pressures may rise to 55,000 or 60,000 CUP!

U.S. manufactured paramilitary ammunition intended for civilian consumption is purposely loaded down to SAAMI pressure levels and bullets are often seated deeper to accommodate the SAAMI chamber. Ammunition
certified to meet Mil-C-9963F (the military specification for M193 Ball) is only available to U.S. government agencies and private security firms under contract to provide security for U.S. government installations.

Imported ammunition of that type is generally loaded to standard military levels and should be fired only in firearms with military dimensioned chambers. To the author's knowledge, the only U.S. manufactured commercial firearms with military chambers are the Colt AR-15 series, the Ruger Mini-14 and Ruger No. 1 rifles manufactured since 1986.

Now, would an AR-15 from certain manufacturers have a SAAMI chamber instead of a Milspec one?

Second, wouldn't an accurized AR-15 with a match barrel and probably tighter chamber be subject to this same problem

Last, would this explain the case head separation in some AR-15s when using the SS109 ammo?

[This message has been edited by Bartholomew Roberts (edited September 21, 2000).]
 
I seriously doubt that other AR makers are making their chambers incompatible with military ammo, since there is tons of surplus .223 ammo around. If this were really a problem, I would suspect that we'd be hearing a lot more about it...
 
I KNOW that both Colt and Bushmaster make their chambers to military specs. In other words, the chambers are looser so they tend to be more reliable. If a military gun were made with a tight chamber, the gun would prob be less reliable under real world conditions - sand, dirt, dust, mud, etc.

I KNOW that Olympic Arms makes their chambers tighter than Colt and Bushmaster. This is to make their guns more accurate. I'm not sure if they actually make their chambers to SAMMI specs, or if it is between SAMMI and milspec chambers.

I don't know about Armalite, PWA, and others.

HOWEVER, I know of many people who shoot milspec rounds in their Olympic Arms AR15s with no problems. I also know many people with milspec chambers that have very accurate AR15s. I'd say that any AR15 should be plenty accurate and reliable enough with either SAMMI or milspec ammo (unless you are a match shooter, or in the ARMY/Marines/etc).
 
THEY ARE EXACTLY THE SAME. YOU ARE ALL CRAZY!

Just kidding...

My Bushmaster has a .223 barrel and is not "mil spec" as far as the chamber is concerned. It does have problems shooting true 5.56mm rounds like Q3131. It won't reliably cycle the action. The pressure is higher and it messes up the timing enough to screw up extraction and stripping of the next round into the chamber.

My mini-14 has no problems with 5.56mm, though.

I have been through this whole issue extensively and I know exactly what the facts are, so do some research before you make a comment like my joke above.

Try searches on TFL and AR15.com. Look for info on Q3131, 5.56mm vs. .223 etc.
 
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