Identifying an AR-15 style lower reciever

[ShadeWPI]

I helped someone out and got an older AR-15 style reciever. I'll try to get pictures up at some point, but I'd like some help trying to identify it.

The reciever is marked over the magazine well:

R.I.A.

Cal 223 - 5.56
MOD XM-15
SN 7815

There are no logos anywhere on the reciever, but The reciever appears to be milled as their are some end-mill "swirl" tool marks on the reciever.

I'd appreciate anyone with any information about the reciever.

 

[JonJ]

Rock Island Armory made by Sendra.

 

[ShadeWPI]

JonJ,

Thanks for the information. I actually managed to track down the Manufacturer.

The reciever was made by Schuetzen Gun Works (Now Olympic Arms) between 1975 (when they moved to Olympia, WA) and 1982 (when they changed their name to Olympic Arms. The R.I.A. appears to be a post retail engraving rather than part of the original markings.

I'm going to contact Olympic Arms and try to find out when specifically this serial number was manufactured, but it's definately Pre-'94

 

[ShadeWPI]

Based on a conversation with Olympic Arms and a little more Research:

The reciever is a Aluminium Billet Milled Reciever made in early 1982 for Rock Island Armory.

The total production run for such recievers (not just for RIA) was less than 8,000 starting with serial number 1000 (Serial numbers 0001 - 0004 were prototypes)