The barrel on one of my uppers has no markings whatsoever on it.  

Is there any reliable way to find out who made it and/or whether it is chambered 5.56 or .223?

Thu upper receiver and b/bc are Colt, but the barrel aparrently is not.

I am mainly concerned with being able to reliably use Q3131A with it...

Thanks, Gentlemen

Quoted: The barrel on one of my uppers has no markings whatsoever on it.   Is there any reliable way to find out who made it and/or whether it is chambered 5.56 or .223? Thu upper receiver and b/bc are Colt, but the barrel aparrently is not. I am mainly concerned with being able to reliably use Q3131A with it... Thanks, Gentlemen

i ask ed the same question several months ago & got very lyttle response, so i presume few here have a clue, my guess is that they are mass produced by most barrel makers & sell them cheaper wythout a name, don't worry about them being safe, they ARE !! one of mine is approaching 7,000 rnds., i have three barrels wyth no markings, they have eaten every 5.56/.223 i fed them except Wolf, they don't lyke steel cases...

you can definitely feed that barrel Q3131 or Q3131A, as for the 5.56, .223.., no big deal !![:D} trust me...... look up SAAMI (Small Arms Ammunition Manufacturers Institute) & click on 5.56/.223 & get ready to read......

thanks, Jack

The only way I know of to determine if the chamber is a .223 or a 5.56 would be to make a Cerrosafe casting and mike it.  

I’ve never done a chamber cast on an AR, so I don’t know how difficult this is.  Seems like it would be pretty hard to get at the chamber without removing the barrel from the upper.

Cerrosafe can be obtained from Brownells.

As CJ says, with Q3131A you should be OK with either chamber.  However, before buying a large quantity, you might get a few boxes and try them through the rifle.  

Firing mil-spec ammo in a .223 chamber will jack up pressures a bit, but most likely won’t cause any noticeable problems.

IMHO blown primers with Q3131A would be a likely indicator of a .223 chamber.

Sticky extraction or really chewed up case heads MIGHT also be a result of a .223 chamber.

Thanks to you, also, 199.

I have another upper, barrel stamped 5.56. I have had no problems with the Q3131 through it.  

I have not fired anything at all through the upper in question.  Just picked it up a few days ago on a trade.  It is VG, and the price was right...  preban 20" A2, Colt upper, b/bc...

I have always gone BM or Colt, never a problem, as long as they were scrubbed down after a day at the range.

As long as I am at it....

I want a varmint upper.  I have seen the M&A 24", the J&T, the RRA, so on and so forth...

They are alll about the same $$$$

Can you guys tell me where the accuracy is?

I am looking to bust groundhawgs at 250.  Looking for an A3 with optics, thanks...

Call Ms. Cleo.

For future reference, only buy barrels with a "C MP" stamping on them.

The only barrels I have that have no markings, are Wilson barrels. I'm sure there are others, though. If you have a barrel simply stamped 556, it's a good bet to be an Olympic arms. One of my Wilson barrelled weapons(M4 profile) was my main  carbine I used at an Urban Rifle class at Thunder Ranch. I put 1800 rounds through it in a  week and had zero malfunctions other than a couple of mag issues. I used South African ammo bought from Sportsman's Guide. Good luck, and don't sweat it, you will have no problems from 223 vs 556 chamber.

Hack

Quoted: The only barrels I have that have no markings, are Wilson barrels. I'm sure there are others, though. Hack

I have been told this also. I just bought an AR from a guy who said it had a wilson barrel on it. I looked at the barrel to see the twist/chambering, but there were not markings on it.

I picked up a Wilson barrel around 2 months ago,
no markings at all, 16" ChromeMoly.
It's probably 223, so to be safe I put 55 grain American Eagle thru it, 5 boxes/100rnds first.
Then, without cleaning, put some SA thru it while holding at arms length to see if my
preban would go boom. No Problems.

I e-mailed Eric (Ammoman) about SAAMI safe ammo and he said anything he sells is safe to fire in it.
I was thinking of sending it to KKF to be reamed anyway - just to be safe, but I don't know.....