As promised in an earlier post on this thread, I have done more shooting with Big Game powder behind the 140 g. Nosler Partition bullet in my 7X57.
For years I ran a load of H205 with the Partition bullet that got well over 2900 fps. But when I substituted the 140 grain Nolser BT once; the velocity was over 3,000 fps and I got marks on the brass
. (Used that load for a long time with 139 g. Hormady and the 140 Partition. Brass lasted 10 or more loadings, bolt lift was easy.)
Consequently, when the OP mentioned that some sources gave 3,000 fps for the 140 g. bullet, it seemed possible to me.
Today I chronographed a load using 50 grains of Big Game, using two different lots of powder, with the 140 Partition, WW cases and Winchester large rifle primers, OAL = 3.12".
I can find no manual data for Big Game in 7X57, so use 7mm-08 data as a starting point. Nosler gives 47.5 g. of Big Game for 2953 fps with the 140 g. bullet in their 26" long barrel. Ramshot shows 48 grains of BG with the 139 g. Hornady bullet for 2842 fps. in their 24" long barrel at 56,660 psi of pressure.
Nosler shows case capacity of 48.6 g. of water with the 140 bullet in the 7mm-08, and 52.5 g. of water with the 140 g. bullet in the 7X57. So the 7X57 case has more volume than the 7mm-08 (no news there).
Rifle is a 7X57 custom M98 Mauser, action made in 1934 by FN, Douglas 22" barrel. Rifle has a long throat.
Results: Four shots with each lot of powder. Temperature was 56 degrees F. Overcast skies so the ProChrono digital chronograph had good conditions for measuring velocity.
Lot #1: 2969, 2976, 2949, 2969 fps.
Lot #2: 2936, 2930, 2962, 2949 fps.
A month ago I started at 48 g. and worked up to 50.5 g. of powder in 1/2 g. increments using powder from Lot #1. This is when I saw the 50.5 g. load record 3003 and 3030 fps on the chronograph
.
Now lest the flaming and derogatory remarks start; let me say that I do not feel I was pushing things too far. I am only 2 to 2.5 grains above published 7mm-08 loads at 56,660 psi with a rifle with larger case volume and a long throat. - Of course I have no way to be certain because I don't have pressure testing equipment. - But going 2 to 2.5 grains above 7mm-08 data seems reasonable. At no point did I experience a change in bolt lift or see marks the case or anything else to suggest too high of pressures.
DISCLAIMER: IN NO WAY DO I SUGGEST THESE LOADS ARE SAFE IN ANOTHER RIFLE. THESE ARE MY RESULTS ONLY AND ONLY PERTAIN TO MY PARTICULAR RIFLE. AS ALWAYS WORK UP CAREFULLY FROM BELOW.