Different brass - different velocities

[Lefty57]

Had my 7Mag. 700 BDL rebarreled to a Bartlien 3B 24'' 8/twist, gun shoots great. I am developing my hunting load for it. 175 Elite Hunter. I am using 2X fired Hornady brass and 2X fired Peterson, the brass has never been co-mingled. It is cleaned, annealed, sized and trimmed all exactly the same, same powder, same primer, same seating depth, after three consecutive days of shooting 6 rounds from each I now have 18 rounds fired from each. Both are equally accurate close to .5moa. Here's the difference the Peterson is consistently shooting 60-70 fps faster. I am using a Garmin, both casings are shooting an acceptable SD for a hunting round being a low of 6.8 to 13.3fps, I do have to use two different neck bushings to keep tension equal on both. Can anyone tell me what's going on?

 

[lancetkenyon]

Peterson brass is thicker, meaning less case capacity.

Less case capacity w. same powder charge = more pressure = more velocity.

Also, WAY higher quality and consistency with the Peterson.

You should not mix brass brands.

 

[MagnumManiac]

^^^^^THIS^^^^^

Cheers.
EDIT TO ADD:
My custom 264WM has almost 100fps difference if I use Norma brass against identical charges in Winchester brass, the difference between R-P Remington to Winchester is about 15fps to the Winchester.

 

[fseaman.js]

Peterson brass is thicker, meaning less case capacity.

Winner, winner, chicken dinner.

 

[Jakeweb09]

Lance nailed it. Pick one and stick to it, and I'd recommend the Peterson by a landslide