I am putting together my first build, and I need some help. I thought the guys on this forum might have some advice for me.

I have a SP1, (or maybe a M16), slick side upper with a large front pivot hole.

I want to mate it to a small hole Superior Arms lower.

I have looked at a couple of different options, but I would like to hear recommendations from somebody with some experience with this condition.

Thanks,

Mick

I,m starting my second with the same upper but an RRA lower. I,m cccurious to see what options you considered. Im still pretty new at this and need all the help I can get.

Before I got a real SP1 lower, I just used one of the offset bushings from Brownells. BTW, does your upper have the "arrow and R" in front of where the rear sight drum goes? Cant see from the pic.

Mine has that and then C and M down below.?!?!

You'll need the offset bushing to mate the two receivers. Brownell's p/n 231-000-181. I think it's made by DPMS and you'll find it in their catalog too.

It'll take a bit of experimenting to find the proper orientation. I have one rifle I use this on and I added a couple drops of blue locktite to keep it in place. So far it doesn't look like I can get the rifle hot enough to loosen the locktite. Others have recommended epoxy. I guess it's just a matter of how permanent you want the adapter mounted.

Could you fill the hole with JB Weld, then mount the upper useing the rear pin and drill through the front holes with 1/4" bit?
I bought the DPMS bushing, it takes a bit of wiggling to get it back together at times.

I've wondered if it would be possible to machine a plug from aluminiun that's a couple of thousands over size. Then freeze it with something like dry ice and drop it into the upper. After it all evens out in temp it should be pretty well locked into place. Then machine a new hole the correct size and location in the upper.

Doc

Quoted: Before I got a real SP1 lower, I just used one of the offset bushings from Brownells. BTW, does your upper have the "arrow and R" in front of where the rear sight drum goes? Cant see from the pic.

Yes