M16A1 upper newby question

[Luger1914]

I am new to this platform so I have a quick question which I hope is not dumb. I have a Colt SP1 lower ser#164xxx. Will a US M16A1 upper fit. Mainly I am concerned about if the pivot holes line up correctly or not. Some reference books say Colt moved the SP1 pivot pin locations down and back to conform to government requirements. Thank you for your help.

Information

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[browningautorifle]

An SP1 lower and an M16 A1 upper will not fit together without an excentric screw. These are available through various sources on line. The hole on the SPI is far larger and the M16 uppers use a small hinge pin.

[Luger1914]

JIM

Thanks for your response. I actually have a couple of the pins that you describe (large on the ends, small in middle--that unscrew). Got them from Bravo Co. If that's all I need, I guess I'm fixed up.

Charles

[browningautorifle]

Give 'er a try, I think you'll find it's a fit. Cautionary though, it's not perfect. You may have a little grief. I just forget, it's been years since I had mine set up that way.

[Roscoe Snyder]

I used to do this. I don't recommend it. There's no way to keep the nut tight unless you want to risk Loctiting it. If you don't have an A1 upper yet, I'd suggest looking for an SP1 upper on Gunbroker or wherever.

[browningautorifle]

Usually they already have the SP1 upper and lower. They just want to beautify it. I still don't quite understand the fixation with the forward assist. I changed a couple of SP1's over to other configs and they were fine. ie H barrel, sub gun...I just remember there was something strange about the excentric screw rig...

[Luger1914]

Actually, I do not have the upper. This SP1 had an A2 upper on it, but the previous owner for some reason ruined it by grinding out a huge, deep chunck about the size of a quarter from the lower rear of the upper. I don't know why. So I just bought the lower. I may hold out for a SP1 upper or put another A2 on it. I have brand new triangle handguards and a correct stock (came with an A2 stock). Any way thanks for the comments--I had been wondering how to keep that pivot screw tight.

[Roscoe Snyder]

[IMG][/IMG]

This is what I finally did. An SP1 with an A2 Sporter II upper receiver. Same size hole above and below.

[browningautorifle]

Luger, what the grinding was about is that's where the auto sear operates. The military uppers have the recess already milled out. I think you should be able to find what you want without trouble.

[imarangemaster]

I agree. Just search SP1 in the Gun Broker. If you get one and need the large pivot/screw for the SP1, I have a set I can send you. The SP1 upper without a forward assit on the slab side SP1 lower will give you a good model 602 AR15 like used in Vietnam 1962-1964/65, before the 603 model (XM16E1).