Nice day here in Southwest Alaska. Temp is 60* F, just a gentle breeze, no clouds.

Oehler 35p chronograph and a PressureTrace system on my ZKK-602 chambered in .375 Weatherby and built by Jim Brockman. The shells must be loaded from the magazine, the extractor is set up for maximum reliability, and will not snap over a shell base no matter how hard you try.

All cases were prepared the same except the W-W brass was 0.050 shorter. Federal 215 mag match primers and H-414 under 300 grain Barnes TSX bullets.

Here are the specs on all the shells:
3.068" COL (base to ogive of bullet)
4.070" OA (base to tip of bullet)
0.042" to the lands
Necks turned to 0.398" loaded in a 0.401" chamber. Chamber was cut using a Pacific Tool & Gauge finish reamer with an overall 0.125" throat. If I want I can touch the lands with the bullets.

Here are the velocities and pressures using the W-W brass:
1st 2694fps
2nd 2648fps
3rd 2654fps
Note pressures:

Now here are the next three shots using Weatherby brass:
1st 2635fps
2nd 2582fps
3rd 2610fps

Unfortunately my Bushnell boresighter lied to me, my first three shots should have been in the center of the target, they were high and to the right in the dirt. So I bore-sighted by eye and these are the shots using the Weatherby brass:

I was excited about the first two shots, not so much the third. It was while I was standing looking down at my rifle when I saw suspicious marks on my scope tube; it had slid forward roughly one inch under the recoil. And I used a calibrated Seekonk inch-pound torque wrench to set those screws to exactly 20-inch/lbs. according to the directions from Talley. Hmmm. I will have to set the scope back and re-torque to a little better than maximum at 30-inch pounds.

Note the W-W loads are listed by Barnes as starting loads yet the first shot is dangerously high pressure at almost 70k psi. I knew the first shot out of a new rifle would be higher, and had cleaned the bore, but on starting loads? This is why guessing is foolish.

I believe the lower pressures on the Weatherby brass are due to a higher internal volume, but until I weigh the brass, I won't know. It won't help to use water as the cases are shorter.