Gentlemen,
I have an AR-15 which has a heavy A2 barrel. The stamping on the barrel between the front sight tower, and the muzzle reads:
E MP 5.56 NATO 1/7
I know that the MP part of it means magnetic particle inspected, and 1/7 is the twist rate. 5.56 NATO is quite obvious. I take it that the E is the manufacturer of the barrel. If this is true, who is E?

Thanks in advance.

Are you sure it's not a "C"?

I am 100% certain that it is an "E". I just double checked , to be sure. I am quite certain that it is a G.I. barrel. It has the heavy profile from the flash suppressor threads to maybe 1/2 " behind the front sight tower. Then it is quite a bit smaller in diameter clear back to where the chamber area is. Also, the chamber and bore are chrome lined. If you look in the chamber, the chrome lining is very visible. And looking at the muzzle end, there is a silver/grey halo around the bore. The entire exterior of the barrel is dark grey parkerized. I have had this barrel on my AR for probably the last 8-10 years, so I doubt that its a Bushmaster. I thought they were the only ones doing chrome lined bores and chambers.

The mystery continues....

This has gone around at least once before - try a search.  I think (but am not sure) that "E" is Elisco Tool and Machine or something like that.

Spares contract barrels.