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.
(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
(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.