280 AI weird groups??

[Montana'eer]

I have a fairly new .280AI. 700 trued action mated to a Brux barrel, heavy contour and in a McMillan Rem hunter stock. I had the same problem. I had found a couple powders that worked using Peterson brass and Federal TA 155 bullets. However same as you- 2 touching one flyer. At about the sane round count as you- I cleaned the barrel down to zero (completely) and took it to my gunsmith. He scoped it and about 3/4 towards the muzzle end there was a mar down the rifling about 3"-4" in length. We sent it back to Brux and apparently they failed to do the final lapping. Got it back and it's better- but not bug hole better. Sub moa at 100yds.

Check your barrel would be my advice.

 

[Jeremy Henderson]

I had the same problem with my 6BR. What I found was measuring each case I had a few that were.002 longer trimmed to the others and the flyer stopped. Hope you get it figured out.

 

[Rem81]

My 25-06ai has similar problem. First shot be the odd one. Tried all kinds of bullets and switched to hammers and problem fixed!!! Rifle only likes hammers, that's ok cause they shoot little bug holes.

 

[Texis]

Update…
I pulled the rifle apart, bedded the recoil lug and also found that the stock had some paint from the OEM slightly over the aluminum frame at the rear bed points. This was enough to keep the action from making solid contact with the frame. I removed the paint with the tip of a small sharp knife. This allows the receiver to make solid contact with the aluminum frame.
Also discovered the trigger was making very slight contact with the bottom metal.. fixed that.
I changed out the firing pin spring back to the original, removing the 18lb spring.
I believe I'm on the right path based on the first group. First shot was out (arrow). This was to be expected as the action settled in. Then fired 5 shots. The 5 shot group printed 1.100, not a great group… BUT very spread and nothing weird! It produced a nice dispersed group.
I feel like I will be able to now tune the load as it's has different harmonics properly bedded.
Very encouraged to NOT get another weird group.

 

[Texis]

BTW I decided on using the 160 ABs that were running 2900. I'll do a ladder in 1/10gr increments moving up from 58.7gr.

 

[Texis]

Gentlemen,
Thanks for all the inputs, the rifle is shooting. Deep clean, lug bedded and other bedding cleanup.
Just put 6 shots in .750" with 160 AB at 2900 and nothing weird! Certainly not bench rest and I will be validating with larger sample size groups.. I'm happy, more than capable to 500yds on the upcoming mule deer hunt if I can do my part.

Again thanks for the inputs, doubt I would have explored the bedding issues without the suggestions.