Accuracy problems with new SPR

[BlackdogGS]

I built up a SPR using a matched CMT upper/lower, LaRue trigger and LaRue 18” 1/8 twist Stealth barrel. Scope is a new Viper 5-25X50 in a Night Force cantilever Mount. When shooting MOA challenge targets (5 one inch dots at 100 yards) it is MOA on 1 or 2 but the others are around 2”. I’m shooting from a bench with a bipod and bag. I’ll get an occasional 1/2” group but the next will be over 2”. All shots feel dead on. I’m using 69 and 77gr SMK’s over CFE223 or Varget. I’ll switch out the scope next. Any ideas?

 

[VegasHKShooter]

Assuming you’ve checked all the usual culprits: mount loose, barrel torque, flash hider tight.
I’ve seen a couple small things with gas guns. Couple times I’ve seen front picatinny mounts put on (to hold bi-pods etc) where the mounting bolts hit the gas block under flex. Guy shoots one group it’s .6 moa. Lays down again, loads the bi-pod a tiny bit different and bam....bolts touch gas block/ barrel....groups go to shit. It’s worth a look.
Another thing: some guns do not take bi-pod loading very well. Causes flex in the upper receivers. Check that you have zero load on your gun as your shooting. May be a finicky upper.

Just a couple small issues I’ve seen pop up over the years.

 

[AMGtuned]

New barrel also? They definitely do speed up in time. Takes no less than 50 rounds, and usually up to 200 rounds. Just my personal observation, and could potentially be your culprit

 

[Steel head]

Check your gas tube.
Make sure it’s cleanly interfacing with the bolt and not rubbing.
That can cause mysterious accuracy issues.
Check Gas block clearance as well

 

[BlackdogGS]

New barrel also? They definitely do speed up in time. Takes no less than 50 rounds, and usually up to 200 rounds. Just my personal observation, and could potentially be your culprit

Yes, new barrel but I have over 200 rounds through it.

 

[AMGtuned]

I had a gas port burr throw some serious fliers on a barrel once. There is a thread on here with others discussing a similar issue during break in

 

[flyfisherman246]

I had this problem for years and could not figure it out. Drove me absolutely nuts. Said I was done with AR's a million times over. I have an SLR hand guard and an SLR adjustable gas block. It looked like it had plenty of clearance, like .100" at the closest point. I also just assumed SLR would make their gas blocks to fit under their rails. Somebody made the suggestion I just try a smaller block even though I was sure it had plenty of room. So I swapped it out for a standard low pro gas block and it was a miracle. For the first time ever my ar15 actually shoots like a bolt gun. It has a cradack barrel on it and it shoots under an moa every time now. No flyers, no weird shit. After about 3 years of trying every ar part available and every bullet powder primer seating depth combination, this was the fix. Now every bullet shoots pretty decent out of my rifle. I have a buddy with the same exact set up except a WOA barrel. It has always shot about 2 moa or so. I swapped the gas block, threw some of my random hand loads in his rifle, and put 5 rounds into one little hole. Every group after that was right on with his rifle as well. The zero shifting, bad groups, unexplained flyers are now all gone.

What is your hand guard and gas block set up?

 

[AMGtuned]

I had this problem for years and could not figure it out. Drove me absolutely nuts. Said I was done with AR's a million times over. I have an SLR hand guard and an SLR adjustable gas block. It looked like it had plenty of clearance, like .100" at the closest point. I also just assumed SLR would make their gas blocks to fit under their rails. Somebody made the suggestion I just try a smaller block even though I was sure it had plenty of room. So I swapped it out for a standard low pro gas block and it was a miracle. For the first time ever my ar15 actually shoots like a bolt gun. It has a cradack barrel on it and it shoots under an moa every time now. No flyers, no weird shit. After about 3 years of trying every ar part available and every bullet powder primer seating depth combination, this was the fix. Now every bullet shoots pretty decent out of my rifle. I have a buddy with the same exact set up except a WOA barrel. It has always shot about 2 moa or so. I swapped the gas block, threw some of my random hand loads in his rifle, and put 5 rounds into one little hole. Every group after that was right on with his rifle as well. The zero shifting, bad groups, unexplained flyers are now all gone.

What is your hand guard and gas block set up?

So was it barrel whip? Or loading the bipod and handguard flex?

 

[BlackdogGS]

I’m using a Geissele slim hand guard and a LaRue low profile gas block. I had the guard off yesterday and couldn’t see any contact points. Some gas escapes where the gas tube enters the gas block and I noticed a scorched mark on the inside of the rail but no signs of contact.

 

[BlackdogGS]

 

[BlackdogGS]

I might try receiver lapping. Can’t hurt.

 

[Triple D]

Sounds like what I’ve seen from newer LaRue barrels. When the groups open up, is it after you’ve got 7-8rds through the barrel and then it just starts shifting in the point of impact? Mine would start to shift low and left. Let the barrel cool for 5 minutes, the POI would be back where it originally was for 2-3 shots before it drifted again.

I pulled the LT barrel, replaced with a brand new Rainier Match, used all of the same components and was getting consistent MOA groups. I did this because I thought the rail was contacting the gas block, but I’m fairly confident that it’s just the barrel.