Flyers and erratic velocity spikes

[distantfoe]

I'm working up a load for a 7mm rem mag. The gun wears a 27" Bartlein 5r barrel. The gun will be a designated hunting rig so 180vld Berger Hunters were my first choice as large deer and elk are on the agenda.

So far I've ran ~200 rounds through it using cci250s and Retumbo in once fired RWS brass. I believe the rifle groups fairly well at ~.5moa with the exception of 10-15% of rounds fired are flyers well outside the group and spike to 100fps over other rounds.

To date the gun seems to group better jumping the vld's 40-80 thousandths at 69-71 grains. The es was terrible at lighter charge weights but tightens up at 69-71 with the exception of these crazy high velocity flyers.

Bore scoped the barrel today with no indication of a problem. Brass appears to have enough clearance as fired cases measure ~.004 larger than loaded rounds. Runnin .0015-.002 neck tension.

Could this be a primer issue, should we give standard LR primers a try? Plan on hunting in temperature down to 0.

Any ideas would be greatly appreciated!

 

[bsumoba]

you will need LR magnum primers for Retumbo. You will probably get ignition issues with regular LR primers.

you can try different powders, anneal your brass, or use a more stable shooting position to mitigate flyers.

 

[wapiti25]

I shoot a 7mm mag for hunting with 168 VLD Bergers and use CCI 250' and no problem. I would look at the brass that has flyers, maybe flash hole size. Measure the neck wall thickness, I use Winchester that is turned to about 60% clean up or better and I do anneal the necks. I would look at shooting position if this is a light rifle. What ranges are you shooting and what is the average group size when it throw's one out? You might try sorting your bullets base to ojive, just a thought. My buddy and my self have killed two moose and one elk with the 168's, one moose was 512 yds and the 6X6 elk was 435 yds one shot kill's. I found the bullet under the hide on the far side of the moose that I killed at 200 yds. Both moose were shirus bull's.

 

[distantfoe]

you will need LR magnum primers for Retumbo. You will probably get ignition issues with regular LR primers.

you can try different powders, anneal your brass, or use a more stable shooting position to mitigate flyers.

I completely agree, Retumbo at compressed levels calls for a magnum primer.

Will definitely try annealing the brass. So far I've tried H1000 which switching to Retumbo cut group sizes in half. Early in load development shooting position was an issue since addressing the issue group sizes have significantly improved yet I really can't explain the 100fps+ spike in velocity

I shoot a 7mm mag for hunting with 168 VLD Bergers and use CCI 250' and no problem. I would look at the brass that has flyers, maybe flash hole size. Measure the neck wall thickness, I use Winchester that is turned to about 60% clean up or better and I do anneal the necks. I would look at shooting position if this is a light rifle. What ranges are you shooting and what is the average group size when it throw's one out? You might try sorting your bullets base to ojive, just a thought. My buddy and my self have killed two moose and one elk with the 168's, one moose was 512 yds and the 6X6 elk was 435 yds one shot kill's. I found the bullet under the hide on the far side of the moose that I killed at 200 yds. Both moose were shirus bull's.

Have not considered a flash hole issue, will investigate this. Neck wall thickness measures .0115 -.0125 throughout the lot. I had always believed .004" clearance with .0015 -.002 tension to be enough, but could be mistaken.

Group size doesn't concern me as much as the 100+fps spikes in velocity.

 

[distantfoe]

Well this issue was completely eliminated by switching to Federal 215 primers. ES went to 20fps or less using 69-72 grains of retumbo with nothing over 1/2moa @ 250 yards.