Took my M1A apart tonight to send the bbl'd receiver back to SA for a bolt replacement on recall. I'm new to M1A's so I've been reading these forums for a while for pointers. I thought from what I've been reading, that bbl's were marked with the manf. My bbl has no markings on it. So is this an original SA or what? Op rod is TRW as is the hammer. The side of the trigger group is serialed with OM-N behind it. Is the just the hammer a TRW or is the whole trigger group TRW? Thanks for help with my many newb questions! Greg

During M14 production, TRW only made eleven parts.  Like H&R and Winchester, they subcontracted a number of parts.  It appears that TRW later made replacement M14 safeties.  Your trigger housing was made by a subcontractor for Winchester, possibly named Nichols Machine.  

When your rifle was made, Springfield Armory, Inc. was out of USGI M14 barrels.  They bought Wilson Arms blanks and machined them in-house to produce standard contour non-plated barrels.  These are good barrels and good to go.  M14 chromium plated barrels will have the number 7790190 on them as well as other markings.  Sometimes, the USGI barrel markings are found under the hand guard where you cannot see them unless the hand guard is removed.  Be advised this is a short answer to your question but I HTH.

Different: I did take the handguard off so I could see all of the bbl. No markings at all other than a 15 stamped on top of the bbl at the rec shoulder. But anyway thanks for your answer and the ones you've given on my other questions. Much appreciated. And thanks to everyone else (most everyone anyway) who have taken the time to respond and help me out. Greg

You have a commercial barrel.  Again, if it is standard contour it's a Wilson Arms blank machined by Springfield Armory, Inc.  I had one of these on my select fire M1A when I bought it.  I found out through a Freedom of Information Act request that I'm the eighth person to own this NFA Registered "machine gun."  Even so, this barrel with a TE of 5 when I bought it was dead on accurate in semi-automatic.  

Just one more time! LOL I don't know what a standard contour is, but the first 1 3/4" is 1.1", down to  1.070" out to within a couple of inches from the end of the handguard, down to .900 past the gas system, then .600 the rest of the way. Like I said, I don't know what any contours measure on these rifles, but you probably do. Thanks again. But just remember, you keep answering my questions, and I'm liable to keep asking! Greg

Quoted: Just one more time! LOL I don't know what a standard contour is, but the first 1 3/4" is 1.1", down to  1.070" out to within a couple of inches from the end of the handguard, down to .900 past the gas system, then .600 the rest of the way. Like I said, I don't know what any contours measure on these rifles, but you probably do. Thanks again. But just remember, you keep answering my questions, and I'm liable to keep asking! Greg

By your description, it is a heavyweight barrel.  If so, it's most likely a Douglas or a Wilson Arms barrel.  In the 1980s, Hillside Manufacturing in Pennyslvania turned the Wilson Arms barrels and Glenn Nelson in Georgia machined the Douglas barrels.  This is ASSUMING this is the original barrel to the rifle.