AR15 lower to upper mounting lug clearance?

[Drew Eckhardt]

Is there any reason not to make a lower with side to side clearance for upper lugs on the tight side of the allowed .500 +.000,-.004 range?

I've been spending some quality time with a vertical milling machine and am about to make the front cut on one paper weight.

[a308garand]

If you know the exact measurement of your upper receiver lugs, I don't see a problem.

If you switch uppers to one that has a lug on the plus side of the specs, then you may need to alter it to fit your lower.

Some makers "fit" their upper & lower a bit on the tight side and charge you a bit more for the service.

Its your rifle, go for it.