peterk123
NES Member
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?
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Upper/ lower fit
- Thread starter peterk123
- Start date
peterk123
NES Member
Yes.
Golddiggie
NES Member
As long as it's not sloppy as hell, it should be fine. Some lowers have set screws to help tighten up the fitment. That could just be for user aesthetic more than anything else. Personally, I like them snug so things don't rattle.
peterk123
NES Member
Usually not. This is a curiosity question. Just trying to learn.
FalArAk
NES Member
I would think a loose upper/lower would kinda suck if you are shooting paper and trying to get a tight group.
Other than that, to me if its loose its sloppy tolerances from the manufacturer.
And then there is LMT lol
Even if you have the perfect load perfectly in the chamber, you still have to hold the shot. A wiggly upper to lower fit makes holding the shot more difficult. Just my opinion and not necessarily fact, but I would think such slop introduces negative and variable dynamics upon ignition.
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.
gerrycaruso
NES Member
An Accu-Wedge or an O ring will likely tighten everything up but may not be necessary. When my son was in the Marines, his M16 was quite loose but was still capable of hitting the head of the 500 yard target. They didn't use optics then. He said hitting the body was too easy. The rubber is a cheap and easy fix. Try it and see if it makes a difference.
Upper/lower fit has nothing to do with mechanical accuracy. Think about it: all the lower does is apply a hammer strike to the firing pin, which is in the upper, along with all the other things that matter: barrel, barrel extension, BCG, gas system, sights.
It MAY effect headspace between your ears, though. It's one of those things: if you THINK it matters, it matters.
It MAY effect headspace between your ears, though. It's one of those things: if you THINK it matters, it matters.
Will do- I'll post something later, maybe drag out one of my FDE or Kodiak uppers so you can see the o-ring better. I don't use it on all my AR's but if it's a match gun and there is some wiggle room, the o-ring takes care of that. If a combo of a particular upper and lower has enough play to bug me, I'll put an o-ring in there for that too.
Golddiggie
NES Member
IME, the accu-wedge is a complete waste of money. I'd rather drill and tap a lower for a nylon tipped set screw (or grub screw) under the rear takedown pin. Then again, I also have the setup to DO that. 
Not that it would be difficult for most anyone with at least some basic home tools (drill press, with a decent vise, at the very least). I have some spare screws for this as well (1/4-28) along with PLENTY of taps and the correct size drill bit. 
Also, I've been seeing a LOT of all but the cheapest lowers come with this as part of them already. Or at least the billet lowers are.
I did try using the accu-wedge several years back (ok, about a decade ago) but I can't imagine the design has changed in the time since then.
Keep in mind, you'll want at least a small amount of play between the upper and lower so taking them apart isn't a complete pain in the a$$. Too close a fitment and things won't move properly when needed.
Not that it would be difficult for most anyone with at least some basic home tools (drill press, with a decent vise, at the very least). I have some spare screws for this as well (1/4-28) along with PLENTY of taps and the correct size drill bit. Also, I've been seeing a LOT of all but the cheapest lowers come with this as part of them already. Or at least the billet lowers are.
I did try using the accu-wedge several years back (ok, about a decade ago) but I can't imagine the design has changed in the time since then.
Keep in mind, you'll want at least a small amount of play between the upper and lower so taking them apart isn't a complete pain in the a$$. Too close a fitment and things won't move properly when needed.
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If you have a steady position and grip, removing the wiggle during shooting, then it should not have any effect on accuracy.
However, if you have a loose grip on the rifle, it could affect accuracy. The barrel in a rifle begins to move before the bullet exits the barrel. The heavier the rifle and/or more solid your position, the less it will move. Loose support/grip on the upper/handguard and it would be easy for the upper to start moving before the bullet exits the barrel.
Ultimately it’s a non-issue. For the vast majority of people shooting an AR, any accuracy change will be within the noise. And for the tiny percentage who may notice it, they’re going to be holding the rifle firm enough anyway.
However, if you have a loose grip on the rifle, it could affect accuracy. The barrel in a rifle begins to move before the bullet exits the barrel. The heavier the rifle and/or more solid your position, the less it will move. Loose support/grip on the upper/handguard and it would be easy for the upper to start moving before the bullet exits the barrel.
Ultimately it’s a non-issue. For the vast majority of people shooting an AR, any accuracy change will be within the noise. And for the tiny percentage who may notice it, they’re going to be holding the rifle firm enough anyway.
@Reptile Here's the #7 O-ring. You want buna rubber, not viton. They can be found at local hardware stores or in bulk packs on that website owned by the guy with the Spaceballs rocket.
They go over the front trunnion. Some trunnions fit very close to the handguard, such as the Aero Atlas below. You can stretch a rubber o-ring to make it thin enough to pop over the trunnion or use an old hotel key card etc. to push it. Viton won't do this- that's why you want rubber.
@peterk123 I don't bother doing this with range blaster carbines, AR pistols, and SBR's because it's really not necessary. For my match .223's, 6.5 Manbun, and 6mm ARC's- I absolutely will use the o-ring if the lower doesn't have a tension screw. These are all sub-MOA and a couple are consistent half MOA.
They go over the front trunnion. Some trunnions fit very close to the handguard, such as the Aero Atlas below. You can stretch a rubber o-ring to make it thin enough to pop over the trunnion or use an old hotel key card etc. to push it. Viton won't do this- that's why you want rubber.
@peterk123 I don't bother doing this with range blaster carbines, AR pistols, and SBR's because it's really not necessary. For my match .223's, 6.5 Manbun, and 6mm ARC's- I absolutely will use the o-ring if the lower doesn't have a tension screw. These are all sub-MOA and a couple are consistent half MOA.
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These shims are another option for those interested in a tighter fit. I got one to try for the heck of it and it works well. I think it’s cleaner than the accuwedge. Though, you need to be a little more detail oriented when fitting it since it doesn’t have the play that an accuwedge has.
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556USER
NES Member
Do not confuse the terms upper and lower to describe the parts that a bikini covers.
Golddiggie
NES Member
If anyone wants to drill and tap their lower for a set screw, shoot me a message. I have an AR15 jig as well as all the other needed items. Initial setup, for the first one, will probably take the longest. Then running the tap. I have more than a few 1/4-28 taps on hand.
Garys
NES Member
peterk123
NES Member
Bodhisattva
NES Member
Anyone mention these?
www.triggershims.com
AR-10 AR-15 Shims for Pivot Pin, Bolt Catch, Barrel, Trigger
AR-10 and AR-15 Shims for Pivot or Take-Down Pin, Bolt Catch, Barrel, Suppressor or Compensator Shims, Trigger and Sear Shims, Mil Spec & Large Pin Colt Shims
Anyone mention these?
AR-10 AR-15 Shims for Pivot Pin, Bolt Catch, Barrel, Trigger
AR-10 and AR-15 Shims for Pivot or Take-Down Pin, Bolt Catch, Barrel, Suppressor or Compensator Shims, Trigger and Sear Shims, Mil Spec & Large Pin Colt Shims
I made my own years ago . Those will take out most of the lateral slop and a good option if taking down the upper is done at home on a bench. Out in the field, good luck.
There are a number of ways to remove the slop . I think the best method would be to weld both holes in the upper . ,mate the halves together and then ream a new holes . No vertical play and lateral play should be reduced as well.
Or ... buy matched sets.
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