Help ID shorty upper

[Dano5326]

Happened upon a 11.5" upper of unknown origin. If you know who makes this please tell

-no maker marks, of any sort, or twist on barrel
-no m4 barrel extension
-no marks on upper reciever itself
-Marked, on the lower rear left side of front site base, with what appears to be a crown.

Thanks

[Robb Jensen]

Happened upon a 11.5" upper of unknown origin. If you know who makes this please tell

-no maker marks, of any sort, or twist on barrel
-no m4 barrel extension
-no marks on upper reciever itself
-Marked, on the lower rear left side of front site base, with what appears to be a crown.

Thanks

Dano5326,
That sounds like a Bushmaster FSB (I've only seen the crown on Bushmasters) and is very likely a Bushmaster barrel. Their barrels are usually marked something like this B MP 1/9 5.56 NATO, I'll look when I get to work IIRC they don't mark their stainless barrels. It might be a cutdown Bushmaster 14.5" or 16" and the marks were on the cutoff portion. Bushmaster doesn't use F height FSBs so you'll need the .040" taller Bushmaster front sight post (they are about $5.50ea) to zero correctly on a flat top upper without the front sight post nearly falling out.

If there isn't any marks on the receiver it's probably not a Bushmaster upper receiver. They usually have something that looks like a skeleton key (Cerro forging), a small birdhead (Cardinal forging) or an A over a H (Anchor-Harvey forging). It may just be a FrankenUpper.