I tried these .525 ogive 115 NPTs out today in my .257 Roberts and I was very pleased!
My rifle is an old Rem 722, with a 6X Leupold M8 scope, and a repurposed short-action Rem 700 ADL beechwood stock I fit to it (floated after the first 2" of barrel shank), since its original stock had been cut back very short at some point in its life.
I checked the fit of the ogive to my rifle's throat and was happy to see that when seated to .025" off the lands (2.81" COAL), the mouth of a case trimmed to the standard 2.223" lands smack in the center of the cannelure. It seems a perfect fit to this cartridge (I did not crimp my test rounds).
Mule Deer made a recommendation for Ramshot Magnum in the Roberts over on the Sisk thread on how much he loves Big Game, and I decided to try out Magnum, since I have 10 pounds of it on hand.Case full of Magnum!
I did not use anywhere near as much as was referenced above but I still got a lot more velocity than I expected.
I couldn't find any pressure-tested data for the 115 NPT with Magnum, but Ramshot lists a max of 51.1 gr with the 117 Sierra, providing 2900 FPS with only 56.5K PSI. With the slightly lighter bullet, +P cases, and a rifle capable of handling 65K PSI, I felt pretty comfortable going a half grain over that as max for my little first test run. Here's the load:
Older, once-fired Federal +P .257 Roberts cases (from the days of the red primer sealant), old white-box CCI 250s, the .525 Ogive 115 gr .257, and 49, 50, 51, and 52 grains of Ramshot Magnum. COAL was 2.81", putting the bullets .025" off the lands.
3-shot groups are at 100 yards. Temp was 60F. Velocities surprised me:
49 - 2910 FPS, SD 11, 1.16"
50 - 2984 FPS, SD 15, 1.07"
51 - 3019 FPS, SD 6, 0.80"
52 - 3071 FPS, SD 8, 0.90"
I almost didn't fire the last three rounds due to the exceptional velocities, but there were just no other pressure signs whatsoever. I used my little finger to open the bolt from the firing position on all the shots and they all felt the same, but there is no getting around the fact that those are some way higher speeds than I am used to! But, then again, the highest published data for the Roberts I have run into is 58K PSI. I will try the 51 gr load again, and I will use the same cases again as today's 51 and 52 grain loads to be sure I keep tight primer pockets. Mule Deer got around 2950' with Magnum with the 120 Partition so I reckon 3019' with the 115 is not too out of line. I also have some new Fed +P cases and can do a check of CHE as well - not the end-all, but it's one more piece of data to consider.
If somebody here can run Quickload, I can measure the parameters needed for the run - just PM me what is needed. I'd probably need to convert the COAL to what it would be with the "normal" 115 NPT loaded with its base at the same point as the .525's base, since I doubt Quickload has the .525 in its database.
Looking forward to reading what others learn about loads for this bullet.