Upper/ lower fit

[Davidk]

The slop doesn’t effect accuracy of the rifle, but it makes harder to shoot accurately

 

[42!]

Does tight really matter that much? If it delivers the bullet into the chamber smoothly all that is left is for the hammer to do its job. So what does a really tight fit provide?

With 2 of your 3 points of contact on the lower, any play will affect accuracy, whether it's enough to matter to you, well that's a matter of opinion. For me, anything I an do to reduce the variables, within my budget, is worth it.

Just get an Accu Wedge for every build. It's the cheapest and simplest solution that does the job perfectly of tightening up the fit. They come oversized; just shave a bit off the bottom of the wedge until you have the right fit.

The ARs I've done with the basic Aero Precision lowers had a perfect fit, but the reason I use these is the tension screw they have to remove play between the upper and lower.

Also, in complex systems, big problems are usually the result of a number of small variables, play between any 2 parts is a variable. More play equals more variation. Obviously you can't remove all variation (play), but if you want it to run consistently, reduce the variation as much as possible.

And for those that will say they "had" to have slop for it to function. You are just covering something being out of spec, and introducing more variation, which means lower accuracy and ultimately less reliability. If you're OK with that, that's great. I'd rather find the problem than just set the bar lower. To each his own.