AR Upper and lower fit up

[338 Mollett]

Maybe I'm hard headed but nobody has convinced me that this fit up loose or tight doesn't affect accuracy .

 

[Txhillbilly]

I've never noticed any difference in the accuracy of any of mine. I've swapped upper's and lower's to test that theory, and they always shot pretty much the same as with their original state. Some have a little play, others are very tight.
If it bothers you, there's always the accu-wedge to take up the slop.

 

[SecondsCount]

Maybe I'm hard headed but nobody has convinced me that this fit up loose or tight doesn't affect accuracy .

A guy shooting 55 FMJ ball ammo, getting a 2 MOA group, probably won't see the difference but I believe that it affects accuracy. Why would we go through the trouble of bedding an action to a stock if it didn't make a difference?

.

 

[338 Mollett]

This is an AR 10 project in 6.5 creed and there were some issues to work out. For a gas gun it shoots ok but the fit up is horrible . The cause in this case is the diameter of the take down pins and holes. I thought about making my own pins but couldn't find a drill bit to uniform all the holes to even make a pin.The existing is a 80% lower but the holes measure .285 and the pins .275 . Well biting the bullet I ordered an Aero lower and oversized take down pins from JP Enterprises . The hole on the new lower is supposed to be .2795 with the pin at .279 . I don't mind a little honing to get the right fit. It might not change anything at all but I can't stand that sloppy fit. We shall see.

 

[bullseyeshtr]

I shoot XTC rifle comp with ARs and have a few built for hunting. IMHO - this fit really doesn't matter because the sights and barrel are on the upper. If it was really sloppy I would probably try to put in accuwedges or do something. The match rifle I just built has some play and routinely puts 5 shots into 3/8" or small at 100 and have shot enough cleans with both my service and match rifle that it doesn't seem to make a difference.

GW

 

[Walt Krafft]

I never found an issue on the target, but it messed with my head. I added a 5/16-24 set screw behind the grip that pushed up on the uppers pin boss. Locked the upper and lower up tight. Just be carefull you don't break into any other holes when you add it. Did this mod to a couple of dozen lowers for people in the past.

 

[338 Mollett]

I never found an issue on the target, but it messed with my head.

YEP

 

[mac86951]

Maybe I'm hard headed but nobody has convinced me that this fit up loose or tight doesn't affect accuracy .

I've found that it does affect precision and group sizes. It's about getting the same movement under recoil shot to shot. Common to find Accuwedge in use, or "bedding" upper to lower for tighter fit when on a long range line with ARs.

Just imagine a BR stock where the rear bag ride on a loose bag rider. Inaccurate? No not really, but imprecise, yes.

-Mac

 

[Rocketvapor]

I use these shims:

http://www.wheeldiamond.com/NationalMatchShim.htm

Eliminate AR stock slop with a plastic home made shim.

 

[JB10]

I recently bought a savage AR. Where the accuwedge would set is a spring loaded boss that pushes up on the upper when closed. Same concept. First time i seen this.

 

[jelenko]

A guy shooting 55 FMJ ball ammo, getting a 2 MOA group, probably won't see the difference but I believe that it affects accuracy. Why would we go through the trouble of bedding an action to a stock if it didn't make a difference?

.

I've always wondered the same.

But can't find any difference when I tested with and without the accuwedge. Using match grade barrels, match grade bullets tuned to 1/2 MOA.

 

[karrarararararar]

If the accuwedge made a difference, every xtc shooter would be using them. Yet, most don't.

 

[Taildrag15X]

This is an AR 10 project in 6.5 creed and there were some issues to work out. For a gas gun it shoots ok but the fit up is horrible . The cause in this case is the diameter of the take down pins and holes. I thought about making my own pins but couldn't find a drill bit to uniform all the holes to even make a pin.The existing is a 80% lower but the holes measure .285 and the pins .275 . Well biting the bullet I ordered an Aero lower and oversized take down pins from JP Enterprises . The hole on the new lower is supposed to be .2795 with the pin at .279 . I don't mind a little honing to get the right fit. It might not change anything at all but I can't stand that sloppy fit. We shall see.

You should read up on machine processes, I know milling machines are way better today than back in the stone age when I started learning, but some things don't change.

Precision pin or dowel holes are not drilled to final dimension, they are reamed. If you really want to tighten it up, use tapper pins, you won't be able to pop a pin, you'll open it with a wrench.