Tolerance

[cjd3]

So I am currently building my first AR-15. So I don't break the bank at once, I'm getting one piece at time (too bad it will cost more than a dime). I already bought a new lower, and built it up with a RRA 2 stage trigger and the rest just generic mil-spec parts and the nicer stuff I've upgraded on my original Stag.

My concern is fit tolerance, and the awful wiggle. New billet lower attached to my old upper, and it's loose. When original rifle fit very well, no wiggle, it was just solid. Well I just got my new billit upper, and and when attached to the new lower, the same loose wiggle is present. However, when I hook it up to my old forged lower, it's a solid fit. So I think it's safe to say that there is something awry with the lower.

Am I being to intolerant of the manufacturing tolerance? Or is this to be expected when doing a custom build?

Thanks all.

[Dstrbdmedic167]

What lower do you have? And usually unless they are paired you'll never get an exact tight fit. Most billet lowers have an adjustment screw in the grip area that allow you to tighten things up. If not brownells sells a screw that replaces your grip screw to help. You could also use an accuwedge but I'm not a fan of those.

[GOST]

With custom builds this is a problem you can run into. It won't affect accuracy, but is nice to have a good fit between recievers. My forged Noveske upper had a lot of slack with my Noveske Gen2 lower, but my Vltor upper fit it quite well though. Sometimes you'll just need to try different combinations till you find a good fit. You may want to see if your local gun store has uppers you could try to fit to your lower. If not your best bet may be ordering a matched set like those from Mega Arms. Good luck with it, and post pics of your finished rifle.

[cjd3]

It's an SST-15 lower (grenade/blemished). Cosmetically it looks fine, but perhaps the fit is another reason it's discounted.

[Dstrbdmedic167]

It's an SST-15 lower (grenade/blemished). Cosmetically it looks fine, but perhaps the fit is another reason it's discounted.

There is a Allen head screw in the bottom that will allow you to adjust the tightness of upper to the lower. Adjust and see if it helps.

Edit: I don't have one to verify but most billet lowers do.

Looks like this...

[GOST]

I doubt it, with most of your higher end companies blemish lowers they sell are due to finish, not tolerances. You may want to email them and ask if there is a brand who's upper fits better.

[cjd3]

I tried the screw take up, I need to play with it a bit more to find the sweet spot. Otherwise, it's too tight, and removing the take down pin is a pain.

[Dstrbdmedic167]

I tried the screw take up, I need to play with it a bit more to find the sweet spot. Otherwise, it's too tight, and removing the take down pin is a pain.

It's a sweet spot. You could also email Dennis and talk with him. He's good people and I'm sure he'd work with you.