Authentic USGI M16A1 Parts?

[Neal Myers]

Colt SP1 upper will have C M in the recess under the rear sight (right side).

Neal

Information

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[wbaad]

Colt SP1 upper will have C M in the recess under the rear sight (right side).

Neal

Not necessarily. Those are forge marks and there could be a variety of companies making them. Mine says CH
Some earlier uppers had no marks at all.

To the OP.
The triangle over the square box at the front of the upper looks to be the colt verified proof over the c in box inspectors stamp, which would mean that upper left colt assembled as a rifle and test fired.
I vote it's an original A1 colt upper and not sp1 if both attach lug holes are the same size.

https://www.ar15.com/mobile/topic.html?b=3&f=123&t=401263

[garrettbragg12]

Not necessarily. Those are forge marks and there could be a variety of companies making them. Mine says CH
Some earlier uppers had no marks at all.

To the OP.
The triangle over the square box at the front of the upper looks to be the colt verified proof over the c in box inspectors stamp, which would mean that upper left colt assembled as a rifle and test fired.
I vote it's an original A1 colt upper and not sp1 if both attach lug holes are the same size.

USGI Colt 603 XM16E1/M16A1 upper buyers guide Edition II -

So I just got home and the front lug hole is closer to 3/8" from inside to inside. My standard m16A1 upper is close to 1/4" inside to inside. I placed a USGI front lug pin inside to show difference. So I'm assuming that makes this an SP1, however I'm confused because the rear site markings are consistent with a 604.

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