AR-15 lower tight fit

[arizona98tj]

This is a PlumCrazy poly lower. I need to open the indicated area about 10 thousandths.

It appears to be a simple case of tolerance stacking....since the problem only exists with this particular lower and a new upper I got today. This lower and the new upper can be interchanged between my other two ARs just fine.

Anyway, I'm looking for suggestions as to how to proceed. I don't have access to a mill and I'm not looking to have a gunsmith do the work.

 

[rcmodel]

If you are talking about the curved surfaces?
Sandpaper on a round dowel rod or broom handle should do the trick.

If you are talking about the flats down inside?
A plastic lower would be easy inletted / shaved / scraped deeper with a sharp wood chisel.

rc

 

[BBBBill]

What is the measurement between the receiver walls on this vs your other ARs? Mine measure .498"-.500". If you determine that you need to open the lower receiver, then use a small file to remove material equally on each side. That's one spot that you don't have to be super precise, but I would not use a Dremel or other power tool to attempt it. Too much risk of really messing up. File a little and check fit often.

 

[arizona98tj]

RC, my flats are the problem.

BBBBill,
Mine measures .487" between the walls while my upper is a solid .500".

 

[BBBBill]

That works out to about .0065" per side assuming that they walls are equal. That shouldn't take long at all.

 

[arizona98tj]

Finished it up earlier this morning. Took about 10 minutes with a file. Got a nice snug fit....worked just fine. Thanks to all for the input.

On another happy note, went to the local Cabela's this morning and scored an 8# jug of Varget. I also picked up a pound of Benchmark and H322, both of which will be used this afternoon in my first round of 6.5 Grendel handloads. I've got some 90 gr Sierras and some 120 gr Noslers to load.