I'd say you are GTG! We will look forward to positive reports come deer season!
Looks like you're right. The only loose thread I needed to tie up was to shoot this load in some new, unfired Fed cases, in order to take a case head expansion (CHE) measurement, to back up my assessment of no pressure signs. I got some more data on the load in the process.
Recapping, the load I have settled on is:
.525" Ogive 115 Partition
Older stock Federal .257 Roberts +P cases
50.8 grains of Ramshot Magnum
Fed 215M primer
OAL of 2.81", which places the bullet .025" off the lands.
I have shot five 3-shot groups so far at 100 yards with this load. Largest was 0.94", smallest was 0.75" average of 0.81"
A composite of today's 9 rounds have 8 inside 0.93", with one outlier which opened the 9-shot composite up to 1.53". That outlier, BTW was the source of the 0.94" 3-shot group alluded to above. Except for that group today, all 4 other groups with this load were 0.75" to 0.79" - very consistent.
Velocity with the Fed 215M is smack on 3000 FPS. In earlier tests with some 25-30 year-old CCI-250s, I got about 20-25 FPS faster.
I had a box of N.O.S. Federal .257 Roberts +P cases, of the same vintage as the ones I've been working with, and used these today to check CHE. Average CHE of new brass was .00038". This is pretty good. Max loads typically show .0005" or more. This supports my observation that there seem to be no pressure signs with this load.
Ramshot has no data for the 115gr, but lists a max of 51.5gr/Magnum with the 117gr SGK, at 56.5K PSI, which comports well with my feel and measurement.
Hope this helps someone else get a good load with this bullet too.
Cheers,
Rex
