Does Play between upper and lower and accuracy?

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Bgd
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Does Play between upper and lower and accuracy?

Post by Bgd » Tue Jan 28, 2020 12:45 am

I can't seem to get better than a 4 inch group at 100 yards no matter what I try. Different bullets powders and charges. I am using Anderson upper and lower, silent captured spring, geissele SSA trigger, xcalibur 18 inch barrel, LMT enhanced BCG, and an SLR adjustable gas block. I have probably put 2000 rounds through it.

Tonight I decided to swap barrels and I noticed lots of play between the upper and lower. I examined the xcaliber barrel and didn't notice any wear. I still need to shoot it with the new barrel to see if it has any effect.
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dowser
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Re: Does Play between upper and lower and accuracy?

Post by dowser » Tue Jan 28, 2020 11:09 am

Theoretically, the play between the upper and lower should not affect accuracy at all. Sighting and firing all happen on/in the upper.

What sights or optics are you using? Shooting offhand, benchrest, or bipod? What does the crown of the barrel look like? So many other things affect accuracy much more so than the fit between the upper and lower receivers.

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Re: Does Play between upper and lower and accuracy?

Post by rlandry6 » Tue Jan 28, 2020 11:51 am

Yes, it can affect accuracy. The receivers are not a tight fit, they have the time the bullet is in the barrel to move and that movement. If you can not feel or see movement when manually flexing it, you should be OK. Check your scope mount. If you have access to another AR, swap your upper with that one and see if the problem moves to the other gun. If it does, the problem is with your upper, the scope mount, or the scope itself.
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dellet
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Re: Does Play between upper and lower and accuracy?

Post by dellet » Tue Jan 28, 2020 12:44 pm

Whether the play is part of the issue will depend on how much slop and your shooting technique.

4" at 100 yards is terrible for supers, not so much for subs staring out. Hand loads or factory might change my mind.

Before I would have done anything beyond checking barrel torque and sights, I would have bought a box or two of known accurate supers. My go to has always been 120 grain UMC. I have never shot a group larger than 1.5 MOA with that ammo in b probably 20+ barrels.
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Dr.Phil
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Re: Does Play between upper and lower and accuracy?

Post by Dr.Phil » Tue Jan 28, 2020 2:38 pm

dellet wrote:
Tue Jan 28, 2020 12:44 pm
Whether the play is part of the issue will depend on how much slop and your shooting technique.

4" at 100 yards is terrible for supers, not so much for subs staring out. Hand loads or factory might change my mind.

Before I would have done anything beyond checking barrel torque and sights, I would have bought a box or two of known accurate supers. My go to has always been 120 grain UMC. I have never shot a group larger than 1.5 MOA with that ammo in b probably 20+ barrels.
+1
Technically, upper to lower fitment do not create a mechanical accuracy issue

Technique is what will cause problems.
With the MSR (AR15) platform, you have 3 separate recoil impulses.
- Initial Ignition / Firing
- BCG / Buffer Contacting the rear of Buffer Tube
- BCG Returning to Battery

Grip, trigger control, follow through, and body position are much more critical in this platform.
One trick that can help is a slight twist of the pistol grip which will pinch the upper & lower.
The biggest issue that impacts accuracy in regards to upper & lower fitment is psychological.
Perception of movement between the two can have a profound impact on marksmanship fundamentals.
Use of an Accuwedge is typically a good way to relieve any issues.

Troubleshooting any issues is pretty straight forward.
Remove as many variables as possible.
- Use proven factory ammunition
- Use a known good optic
- Have someone else shoot your rifle
If your results are unchanged, then you can legitimately blame the build / rifle.

One additional step that I have been using on my recent builds is to lap and bed the upper receiver.
(As long as your barrel is free floated, you will get a tuning fork effect from the barrel once bedded.)
Since you are already familiar with X-Caliber, look into their B.A.R.T. 2.0 tool.
Image
(It is both a lapping bar for the upper receiver as well as a reaction rod for the barrel extension.)
http://www.x-caliber.net/bart-20

For bedding the barrel, I use the following process.
- Lap and clean the upper receiver.
- Thoroughly clean & de-grease the barrel extension.
- Apply release agent to the inside of the upper receiver.
- Mix and apply DevCon Epoxy
Image
(Ensure that you apply enough to have "squeeze out", but not so much that there is epoxy in front of the barrel extension.)
- Insert and seat barrel into upper receiver.
- Clean off "squeeze out" epoxy.
- Lightly tighten barrel nut.
- Allow to cure to a minimum on 24 hours in a warm environment.
- Inspect, remove any additional epoxy if required.
- Fully torque barrel nut to specification. (Torque and loosen three times prior to final torque.)
NOTE:
If you do this process, I strongly recommend doing so in a way that does not require you to remove the barrel from the upper once you apply epoxy.
The barrel will come out, but there is now a zero clearance fitment.
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don't tell them where they know the fish."
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Bgd
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Re: Does Play between upper and lower and accuracy?

Post by Bgd » Tue Jan 28, 2020 2:52 pm

I am shooting from a bench with a front bench bag with the bravo company handguard resting on the bag. Nothing touching the barrel. Strike eagle 1x6x24 scope. There is lots of slop between my upper and lower. scope rings and scope are not moving rechecked the torque on the screws all good. I will try it on my colt lower 'its tight', and buy a box of 120 umc. hopefully i can get back out to my bench this week. raining today.
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Re: Does Play between upper and lower and accuracy?

Post by superbike1 » Tue Jan 28, 2020 5:28 pm

I'll say that a 4" group at 100 yards is not a result of a loose upper. With my past extensive time in the USMC, I fired many m16's that had lot's of play between the upper and lower and could shoot better than 4" group at 200 yds. If you have sight alignment/sight picture when the hammer falls, theoretically the projectile should be headed to the same POI.

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Re: Does Play between upper and lower and accuracy?

Post by TRshootem » Tue Jan 28, 2020 8:53 pm

In all of the many builds we've done only one was a challenge in accuracy. The barrel was from a reputable maker, just didn't quite finish up well. The accuracy of almost all basic AR's is at least 1 MOA with good ammo and technique. Two things result in really nice shooting rifles: good barrels and nice triggers, and of course optics to take advantage of the potential. They all have a bit of tolerance stacking, some lowers have a threaded hole for the use of a grip screw combo to tighten up the receivers fit. I have noted it makes the owner happy but no real change in the the rifle performance.

Bgd
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Re: Does Play between upper and lower and accuracy?

Post by Bgd » Wed Jan 29, 2020 1:05 pm

Glad it is not anything to do with the slop between the upper and lower. I will try harder at the range. Could be old age and eyesight, but I am not giving up. maybe 6 power and my eyes is not good enough for 100 yards. I stepped the range off at 125 paces so maybe it is closer to 125 yards.

Thanks for the help!! I will update after I can get to the range.
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