Need help IDing an AR upper

[cyclops]

I just purchased a flattop AR upper from a friend. I can't tell who the make is and he didn't know. The only marking on the upper is an "M" just above the barrel attachment point. Any ideas?

[Robb Jensen]

I just purchased a flattop AR upper from a friend. I can't tell who the make is and he didn't know. The only marking on the upper is an "M" just above the barrel attachment point. Any ideas?

It's more than likely a Colt upper receiver. If you look with a flashlight it probably actually has M4 (for M4 feed ramps).

[cyclops]

It may me a colt, but it doesn't have the M4 feed ramps. Somebody told me it may be an FN upper. Any validity to that?

[SinnFéinM1911]

No, Its not a FN.

[cyclops]

OK, so it's not an FN and it may or may not be a Colt. Does anyone else have any ideas?