I know this is a dual post. I posted in "Build your own", but I should have posted in here... Sorry.

I have a Colt "CM" marked A2, auto sear reliefed upper. From the documentation I've read, this is a large hole .316 upper. This looks like it will make a nice auto sear drop in project later, but what lower will work with this upper? I figured a large hole Colt lower, but anything else? And where, can I find large hole lowers? I am under the impression large hole anything is tuff to come by.

From what I've read this is considered a NON- "mil-spec" upper. Does this mean I have to take note on what bolt groups, barrels and other parts I buy for this?

Thanks,
David

Stickman style!

Because your upper has the sear relief, it sounds like it *was* a milspec upper, then someone later drilled it to large hole diameter.   Who knows with Colt.   You'll probably need a very old slabside with no block.

Quoted: Stickman style! i1.tinypic.com/sgpoo2.jpg Because your upper has the sear relief, it sounds like it *was* a milspec upper, then someone later drilled it to large hole diameter.   Who knows with Colt.   You'll probably need a very old slabside with no block.

That's a sexy upp... I mean lower ya got there... I am only going by the markings "CM" and this site www.biggerhammer.net/ar15/uppers/

"Colt owners often refer to having a small or large hole upper receiver (and corresponding lower receiver). Small hole receivers of .250" are the "milspec", but during early production by Colt for the civilian market, they produced rifles utilizing a .315" spec, so as to preclude use of military uppers on civilian lowers. This production lasted until roughly 1993-1994. As a general rule of thumb all Colt "unblocked" lower receivers, are large hole, while pre-ban "blocked" lower receivers represent transition years where occasional variations popped up. "

But the pictures of the "M16 Sear Relief" almost to the bottom is what all of these uppers show.

I have :

1 A3 marked "M4" & "C AF"    -    Colt A3 M4 Flat top
1 A3 none M4 marked "C AF"  -    Colt  A3 Flat top
1 A2 none M4 marked "CM"     -    Colt A2 Carry handle
1 A2 none M4 marked "LK"       -    FN/Kaiser Carry handle

ALL 4 of these uppers have the same cut out as the picture of  the Colt M16 on that link. Even my Bushy has the same cut out...

Thanks,
David

I have the same Colt A2 marked CM upper but my upper half came from a new M16A2 rifle and it have a small 0.250" diameter pivot pin hole size.

You should actually measure your pivot hole size, if it's the same as the rear take down pin then it's 0.250".

If it's actually a 0.316" pivot hole you could just buy an adapter for that maybe at Brownells or any other parts sellers.

As for what lower to get for your upper, any brand lower with the small pivot will work when you use the pivot pin adapter.





If you want something not the usual take a look at Denny's Global Tactical/ Stag Arms lower with SAFE and SEMI selector markings.

Denny might be out of stock of his lowers for now but he have another batch coming soon.


Global Tactical Lower Receiver thread link


If you would rather have a Colt any current new Match Target or LE models with small pivot pin holes would also work or get a pre-ban model with large pivot hole.

I'm using a Colt Match Target HBAR lower with my 'A2 upper.

Damn you and your busty Czech women, Kisara!!!!!    

How much "REAL" difference is there between say, Denny's (STAG) lowers and LMT???

I mean, they want an arm, leg and but cheek for the LMTs. How far out could the tollerances be??

I have looked @ Denny's lowers & I'm considering a couple of them. Not sure if I would get stripped or complete lowers from him. I am very new into ARs... so I would really like to do it right the first time... Learn from other's mistakes.

I will... at some point in the future, be acquiring an auto sear, so I would like to make sure that the rifle I build today, will be capable of full auto tomorrow.

David

Quoted: Stickman style! i1.tinypic.com/sgpoo2.jpg Because your upper has the sear relief, it sounds like it *was* a milspec upper, then someone later drilled it to large hole diameter.   Who knows with Colt.   You'll probably need a very old slabside with no block.

Kisara is the man!!!

Quoted: How much "REAL" difference is there between say, Denny's (STAG) lowers and LMT??? I mean, they want an arm, leg and but cheek for the LMTs. How far out could the tollerances be?? I have looked @ Denny's lowers & I'm considering a couple of them. Not sure if I would get stripped or complete lowers from him. I am very new into ARs... so I would really like to do it right the first time... Learn from other's mistakes. I will... at some point in the future, be acquiring an auto sear, so I would like to make sure that the rifle I build today, will be capable of full auto tomorrow. David

I have a LMT Defender 2000 lower with a 16" LMT M4 upper also.

I also built my Colt Match Target HBAR lower and I removed and installed a new barrel on my Colt LE6721 tactical carbine.

Both Denny's/ Stag/ CMT and the LMT are tops in quality according to most of the members here, they're all made per the blue print drawing dimensions and tolerances.

A lot of great pro custom gun makers like Noveske Rifleworks, MSTN, Denny's Guns, etc. are using these brands of lowers.

If you're just new into ARs, I would suggest you get a completed lower first to avoid expensive mistakes in your build. When you get familiar with it later, you could try to build from a stripped lower.

All lowers could be machined later on for full auto conversion except try to avoid the lowers with the sear block (see Kisara's photo, the sear block could be seen behind the hammer).

Denny's lower would be a good choice because you don't have to change the "SEMI" selector markings, you just have to add the "AUTO" markings later on when you do your legal auto conversion.

Good luck on your project.