View Full Version : Help me Identify an AR Upper!

October 9, 2012, 01:05 PM
I've been working on a budget AR build after winning a complete Frontier polymer lower for $75. After placing a WTT/WTB add for a complete upper locally, I met with an LEO who traded me an older upper he had for my Kahr PM9. I valued my Kahr at around $525 (even though I only paid $325 for it), was wondering how y'all thought I did.

It's a 20" upper with bcg. Looks used but in good shape. Has forward assist and dust cover. He said it was an Olympic arms upper but nowhere is it stamped with the manufacturer. It doesn't have a railed gas block which I find odd for a factory upper, it will be scoped anyway. The only markings are on the barrel where it says:

SUM 5.56
Can anyone confirm this as an Olympic arms? And how did I do on the trade?

for ID:

October 9, 2012, 04:48 PM
Upper receivers aren't marked, with a few exceptions like PSA.

Do you see anything on the barrel indicating if it's 1/7 twist or 1/9?

An upper like that can usually go for anywhere from $400-$550 new, depending on a couple things.

October 9, 2012, 05:24 PM
The first result on an internet search for "SUM 5.56 barrel marking" comes up with an Olympic Arms website. That page says "SUM" stands for "stainless ultra match," supposedly Oly's most accurate barrel. HOWEVER, they also say they only chamber those in .223, not 5.56, so that is a discrepancy. That same page does say that they use a black oxide finish on their stainless barrels, and that requires a bit more care than the usual parkerizing on a normal carbon steel barrel.


In regards to the chambering, this page appears to be an Olympic Arms owners' forum, and indicates that even though the barrel is stamped 5.56, it has a .223 chamber (as per Olympic's site, that would be a SAAMI minimum spec .223 chamber- a VERY tight one).


Therefore, yes, it looks like an Olympic upper (or at least barrel, which is the important part). Moreover, it's a minimum spec .223 chamber, so I'd caution you against using any 5.56x45 ammunition in it. The throat in a .223 chamber is slightly tighter and the pressure spec slightly lower; using 5.56 in the rifle might well be fine, but you're risking a dangerous situation. On the bright side, Olympic Arms has a rep for accuracy, so I'd anticipate if you feed it quality .223 ammo it should be a real tack driver.

October 9, 2012, 05:33 PM
That forearm looks like the one on my old Olympic Arms. I had an upper with one just like that. They have a railed one that fits and it only cost me about $100.00. Mine fit on the same barrel nut as the smooth forearm.

It is $167 now but still not too bad.