Weird diagonal groups from a 308 Bergara HMR-14

FloatPilot

Private
Minuteman
Oct 9, 2023
6
0
Alaska
A couple months back I did an impulse buy on a Bergara HMR-14 in 308. I already have more rifles than I can shoot, so it was the voices in me head.
Anyway, straight out of the box it was shooting two groups a couple inches apart from each other right and left. So I removed pant and texture overspray from the stock pillars and it helped some.
Then I discovered that the newly paint-free pillars had a slightly different radius contour than the bottom of the action. So I had to bed the action. This helped with some of my hand-loads.
Then I had to lap the bore since it was rather rough and collected copper like a penny-bank.
Now I can obtain less than half MOA groups IF I let the barrel cool for a LONG, Long time.
The first two shots will go in the same hole or touch, but unless I wait forever, I end up with diagonal strings. Even with two or three minutes between shots.
The barrel is fully free floating. But the smallest change in temp makes it go nuts. Almost like it has some sort of stress.
These were some load experiments and not the best for this rifle, they are larger groups but they show what the rifle does when it is only slightly warm.
I have shot it with the factory radial brake ( which does nothing) and just the thread protector.
I am wondering if the cryo-freeze idea would work on this barrel.

I have tried:
150gr SMKs (Hates these)
168gr SMKs
175gr RDF Nosler ( likes these)
175gr Nosler Comp
175gr Hornady ELDX ( Really hates these)
180gr Accubonds ( likes these)
190gr SMKs, ( Likes these sometimes. )

For powders so far:
4064
RL-15
Benchmark
BLC2
3031
8280
H-4895
I ran out of Varget before I could progress much.
 

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Thanks for the info link. I took it out to the range again and this time I waited 15 minutes between shots. That gave me a 1/4 inch group.
Then fired 3 shots in one minute before trying a warm barrel group which opened up to 2 inches and the weird diagonal thing again. Plus this rifle saves copper like a piggy bank.
I am still trying to see if anyone here in ALASKA does the nitrogen barrel dip. I hate sending things out of state these days.
 
Thanks for the info link. I took it out to the range again and this time I waited 15 minutes between shots. That gave me a 1/4 inch group.
Then fired 3 shots in one minute before trying a warm barrel group which opened up to 2 inches and the weird diagonal thing again. Plus this rifle saves copper like a piggy bank.
I am still trying to see if anyone here in ALASKA does the nitrogen barrel dip. I hate sending things out of state these days.

If you're going to yank the barrel, do so to throw it away and replace it with a good quality prefit. Shouldered or nut, doesn't matter.

I would not waste time and money on a process that has a marginal chance of working.
 






Budget option:

There are more. Solve the problem, don't dance around it anymore.
 
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It will do this as long as I wait for at least 15 minutes between shots and clean the crap out of it every 5 shots.
 

Attachments

  • Bergara target 200gr Speers, 15 minute cooling.jpg
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