I spent some time at the range today testing some loads for a new-ish rifle. This is a large frame AR with a 22” Creedmoor barrel. The purpose of the rifle is for shooting steel targets out to 900 yards +. I am looking for a .5-.6 moa load.

I understand there are a lot of factors involved in consistently achieving accurate target impacts and for the sake of this discussion, I’d like to pretend that I understand all of them and am a reasonably competent practitioner. I shoot from prone on a mat that is on a concrete pad. I do load forward on the bipod and use a rear bag.

I noticed today that when the trigger is pulled with no round chambered there is a significant movement of the scope on the target—2 to 3 inches while looking at the 100 yard target. I also sometimes feel movement between the upper and lower receiver while loading forward.

The receiver set I am using, a Mega Maten, does have a set screw under the pistol grip that can be adjusted to put some pressure under the rear take down pin lug, working similarly to an Accu-wedge. I did not adjust this to remove any of the play as I didn’t think it mattered to accuracy but now I am not so sure. I have recently invested a lot of time into better brass preparation processes and money into better dies with bushings to achieve better concentricity with hopes of achieving better accuracy. It seems silly to try to get all of the “wobble” out of my hand loads and leave it in the rifle itself.

The question is does the receiver wobble matter? I would imagine that the answer is: It depends. If I can consistently load forward on the bipod with consistent pressure and that consistently holds the upper and lower in a position that does not impact accuracy through the trigger pull and followthrough then the receiver wobble might not be a factor. I have tightened the polymer tipped screw to a point that allows me to pull out and push in the rear take down pin and removes most of the slop.

I know several of you compete with semi-autos. What does your experience tell you about this?

Thank you,
Henryrifle

I don't think it matters.


That being said, I don't see any harm in using the set screw to tighten things up within reason to remove play. Just don't over do it and introduce stress into the upper receiver.

It doesn't matter at all. The movement between the upper receiver and lower receiver doesn't effect accuracy one bit.

Tested, no different with a upper receiver fitting tight to a lower, and one that rattles around.

If you like a more solid feel, use accuwedge or the like. That is what I do in my already tight NRA National Match Service Rifle, I like the solid feel. It doesn't help or hurt accuracy.

ARman

There is no movement between the upper and lower receivers of my 5 ARs. Furthermore, there is no movement between the receivers when I replace a matched upper with the two uppers I bought at later times. My receiver sets are made by Wilson Combat, Black Rain, SI Defense, and Rock River. Even after thousands of rounds, I still need a punch to remove the pins to take down the rifles.

In theory, a little movement between the upper and lower receivers shouldn't affect practical accuracy. But for gnat's ass precision in an AR, I don't tolerate any slop.

You state that dry firing changes the point of aim by 2-3 inches. That's slop to a degree that makes an AK-47 appear tight. Think of your point of impact if you can't control point of aim by any better than 2-3 MOA.

When I dry fire my guns, the reticles just doesn't move when my technique is up to snuff.

If it's true that your reticles bounce that much during dry firing, and if it's true you have the technique to keep the gun quiet, then you have big problem with that rifle.

Receiver slop can affect accuracy if the slop induces movement during firing, or inconsistency in managing the trigger.

I personally do not like the feeling of a sloppy receiver, it's distracting to me so I use accuwedges in my older receivers (that don't have internal tensioners) that are sloppy. Not every combination of lower and upper needs them.

A large part of shooting is mental. And a bad fit drives me crazy so it sure isn't helping.

I have worked on the rifle a lot tonight and what I have found is that the fit of the rear takedown pin is less than optimal but can be reasonably tightened with the set screw AND the front pivot pin tolerance is sloppy. There is no easy fix for that one, I don't think. Tightening the rear feels like it cures 98% of the slack.

Henryrifle

I continued to work on the rifle last night and made sure everything that had threads was loctited, where appropriated, and torqued correctly.

The rifle shot or I shot the rifle much more accurately today without a hint of looseness or slop. Maybe it is all mental but it made a big difference.

Thanks,
Henryrifle

Many rifle builders will tell you that a rifle ... any rifle that has play in the stock will never achieve the accuracy that's it's capable of.

A wedge and the screw under the pistol grip pushes the upper and lower apart, putting pressure on the front take-down pin ... and the wedge, being made of rubber, so it still moves.


Back in the day, before Wilson Combat, Black Rain and many of the speciality build that are available now, a little company called JP Enterprise made a little devise called a AR Tension Pin that I like, it pulls the upper and lower together and my varmint which already had a good heavy free-floated barrel, light trigger and was handloading went from shooting 3/4" groups to to 3/8" groups ... The upper and lower were like one.

It made a believer out of me.

I'll second the tension pin from JP Enterprises.

Does upper and lower fit matter on an AR? No, not until you're trying to wring every ounce of precision out of it.

I just looked in the JPE tensioner pin. There are quite a few reviews talking about it not staying tight and frequent retightening required. Can anyone comment on these statements? I too suffer from a bit of slop on a BCM upper and lower (not purchased together).

kimberKid:

Thank you for the recommendation. I didn't know such a thing existed. I like the idea of pulling the upper and lower together rather than pushing them apart. Have 2 on order.

Thank you again,
Henryrifle

I put an o-ring around the front pin hole on the upper. It'll eventually break with repeated attaching/detaching the upper from the lower but then I just throw another on. Cheap solution for 20 cents an o-ring.

An old trick from a DM course taught at Campbell in 07. Take the brass piece out of stripper clip and put in between the upper and lower when you reassemble. If it improves your performance and doesn't negatively impact the reliability of the weapon keep using it. If you don't see improvement or the weapon will not function, toss the piece in the dunnage pile and drive on.

quote:

Originally posted by snipes:
I just looked in the JPE tensioner pin. There are quite a few reviews talking about it not staying tight and frequent retightening required. Can anyone comment on these statements? I too suffer from a bit of slop on a BCM upper and lower (not purchased together).

When I ordered mine I too ordered two ... one mostly hung on the wall.

I've never had a problem with it coming loose ... perhaps the user didn't get it installed correctly? or perhaps I over-tightened mine. After years of use I did finally replace the tensioner in my varmint gun as it became difficult to remove (maybe from over-tightening) to the point I had to completely disassemble the pin instead of just loosening it ...

My match and varmint guns are the only guns I use the tensioner pin in because
(1) the need of an allan wrench to open or separate the upper from the lower (but that's the only disadvantage of using it).
(2) typically the AR is accurate enough to shoot MOA or very close to it, which is more than most people need.

quote:

Originally posted by CD228:
An old trick from a DM course taught at Campbell in 07. Take the brass piece out of stripper clip and put in between the upper and lower when you reassemble. If it improves your performance and doesn't negatively impact the reliability of the weapon keep using it. If you don't see improvement or the weapon will not function, toss the piece in the dunnage pile and drive on.

Where do you put this piece of brass, across the receiver at the front pin or under the rear pin lug? Or somewhere else?

I only ask as I'd like to give it a try ...

quote:

Originally posted by snipes:
I just looked in the JPE tensioner pin. There are quite a few reviews talking about it not staying tight and frequent retightening required. Can anyone comment on these statements? I too suffer from a bit of slop on a BCM upper and lower (not purchased together).

I was able to use the two that I purchased without incident. If people were having trouble with it coming loose, I suspect user error.

quote:

Originally posted by kimberkid:

quote:

Originally posted by snipes:
I just looked in the JPE tensioner pin. There are quite a few reviews talking about it not staying tight and frequent retightening required. Can anyone comment on these statements? I too suffer from a bit of slop on a BCM upper and lower (not purchased together).

You put i
When I ordered mine I too ordered two ... one mostly hung on the wall.

I've never had a problem with it coming loose ... perhaps the user didn't get it installed correctly? or perhaps I over-tightened mine. After years of use I did finally replace the tensioner in my varmint gun as it became difficult to remove (maybe from over-tightening) to the point I had to completely disassemble the pin instead of just loosening it ...

My match and varmint guns are the only guns I use the tensioner pin in because
(1) the need of an allan wrench to open or separate the upper from the lower (but that's the only disadvantage of using it).
(2) typically the AR is accurate enough to shoot MOA or very close to it, which is more than most people need.

quote:

Originally posted by CD228:
An old trick from a DM course taught at Campbell in 07. Take the brass piece out of stripper clip and put in between the upper and lower when you reassemble. If it improves your performance and doesn't negatively impact the reliability of the weapon keep using it. If you don't see improvement or the weapon will not function, toss the piece in the dunnage pile and drive on.

Where do you put this piece of brass, across the receiver at the front pin or under the rear pin lug? Or somewhere else?

I only ask as I'd like to give it a try ...

You put on top of the sidewall of the receiver perpendicular to the retaining pins. It will fill the gap between the upper and lower thus tightening it up. the piece will actually stick out the side of the receiver. If you try and run it across the receive you would impede the fire control group.

Do remember, I put it up as a means for members to test if upper/lower fit is actually a factor with their rifles ant minimum or no expense. It is a field expedient technique as soldiers will have stripper clips readily on hand if they are issued new ammo. Some upper/lowers are already too tight for the piece to fit in between them, others can be so lose that the piece falls out. If it works and your accuracy improves due to the tighter fit, you should go with an accu wedge or similar product.

quote:

Originally posted by CD228:
If it works and your accuracy improves due to the tighter fit, you should go with an accu wedge or similar product.

Or just try an Accu-Wedge to begin with. They are very inexpensive, can’t hurt anything, and might help. Strangely, though, they cause a lot of controversy: “A total waste of money” is usually the mildest comment their skeptics post, and one would think they were in the same league as asking about drilling holes in a rifle barrel to reduce weight.

In fact, though, reducing “slop” between the upper and lower receivers of AR type rifles is recommended by some knowledgeable shooters. I believe it’s Rifles Only that teaches putting some sideways rotational pressure when shooting the guns to accomplish that (I think I saw it in the Magpul precision rifle DVD). If that’s true, the Accu-Wedge is a cheap and easy way to accomplish much the same thing and without having to think about it.

As for the original question, and as others have already pointed out, it depends on what we’re trying to accomplish. If it’s to help improve our chances of hitting 24×36 inch plates at 100 yards or to make our mag dumps go faster, then I doubt it’s worth the effort.