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I have an Armalite AR-15 in 7.62x39. It has performed well and shot well for years.

I was testing some different powders with Nosler 123gr Varmageddon . Things when well until they didn’t.

Towards the end of the testing, it started to throw a first round flyer, gradually went from 1+ inches to 6 inches. Out of a five shot group I would get the first round 6 inches left and the next for in a 1 inch group.. This happened with more than one powder.

I returned home, cleaned the bore with Wipeout and swapped out the scope.

Same thing, No change.

What could be causing this? Do I need a new bolt?

Also, are 6.5 Grendel and 7.62x39 the same bolt?

Sounds like your barrel extension or the barrel nut is loose. Put the receiver in a vise, grab the barrel and twist it, see if it rotates at all.

6 inches is a lot. I'd be looking for something loose.

You swapped out the scope so rings must be tight. Is the mount tight? I'd check the Barrel nut.

Is this a high millage barrel? Who made it?

How many rounds on your bolt, who made it, and what does it look like? Gas key tight? Edge of the lugs still sharp or rounded? Any cracks? Firing pin retaining pin hole still round, or stretched?

Umm ,I hate to BUT...lets think. 6.5 grendel. Bullet diameter? Maybe 6.5 mm. 7.62x39 bullet diameter? Maybe 7.62 mm...
x 39 is parent case to PPC rounds which the Grendel is. its a 6.5 ppc renamed. Like having for whatever reason, to rename the 300/221 to the blackout...

Not the same rounds FWWI.

I too suspect something is loose. It sets itself on the first shot for a few rounds... and then you do things that make it go back to loose for the first shot. Its not all that uncommon for barrel nuts to not get tightened. Have seen it from top end builders even.

Sorry, I edited my OP

I was asking if the Grendel and the x39 use the same bolt.

If you change powder, charges and the bullet, it could easily be throwing shots. Clean her real good and go back to your old load. If you continue to have fliers with the old load, pull the hand guard and check the barrel nut. Plus the buffer tube nut, make sure the butt stock is locked up tight.
The Armalite is a good solid, stable platform. So would suspect the load differential first.

Started out with a clean bore (WipeOut).
I was testing CFE BLK compared to AA 1680, accuracy and velocity.

First five rounds 29.0gr CFE BLK 123gr Nosler.



Next five rounds, 29.5gr CFE BLK 123gr Nosler



Next five 27gr 1680, same bullet. BTW BLK is 80fps faster than 1680.



Then things started to go to hell. Fliers left and main group move slightly to the right.

I packed up and went home. Cleaned the bore, bolt, swapped out the scope and lubed it up.

I didn't take many pictures, but this is what I was getting with 29.5gr of CFE BLK so I decided to call it quites and contact you guys.

Have you checked the barrel nut yet?

I could not see that it was loose, but I’m no smith

Just dropped it off at my smith’s he is going to check it out

The weak point of your rifle is the bolt. That is what I'd suspect first, then it goes down the list as others have stated. Gas block, gas tube, barrel nut, bad barrel extension and scope or scope mounts.

It should be torqued to a minimum of 40 foot pounds.

Thanks

One of the reasons why I asked if the 6.5 Grendel and the x39 use the same bolt.

I have a Grendel, if they are the same I could just swap it out and test it

thats powder fouling at its finest at a glance. Clean barrel or not. Change powders or even different bullet jacket materials. Saw it often enough in highpower. First shot of a different powder or bullet could... be in the group. Or out of the group. Sometimes 2 rounds were out and then it settled.

That's what I thought. That's why I left the range and went home to clean the bore (WipeOut) and change the scope.

Next day with a clean bore and a different scope, the last target was the norm. I did not take very many pictures, but every five round mag fired, looked like the last target. some not quite so bad, but definitely big time flyers coming from the first round.

The next day I only tested one powder CFE BLK 29 and 29.5gr and two bullets, 123gr Nolser and 123gr SST. No change in powder on day two.

I got myAR back from the Smith.

He took it all apart, found nothing loose and put it back together.

Here is how it shoots now.



This is just one of many loads, this was better than most.

What else could cause this rifle to go from 1+ inches at 100 to 3 inches at 50.

It’s not the optics, I tried 3 different scopes and mounts.

Did you get the carbon out of the barrel? Carbon comes out as best I know, only by scrubbing with an abrasive. Carbon can do wild things until you get it out.
We finally realized when we shot a lot, to always soak a hot barrel with solvent before leaving the range to eat and drive a few hours home. Once carbon sets up its tough.

That or a piece of your barrel came out or something wild like that.

That's unacceptable for even a Mini 14.

Your barrel is trash or your upper is trash.

Accurate uppers can be had now for a couple hundred bucks.

I cleaned it with WipeOut several times.

The Smith took it apart and ran a scope down the bore, he said it looked OK, but cleaned it again.

Something is trash that's for sure, what do you mean by the Upper is trash?

Receiver, bolt, forend?

I'm looking for barrels right now, not a whole lot out their in X39.

Any suggestions?