Sheltowee
Well-known member
Finally got to test some loads through my 257PRC this weekend and thought I'd share a project write-up for anyone interested. I set out with the goal of building a heavier rifle that could do double duty as a Plains deer/antelope and 1000+yard ringing steel rifle. I chanced upon the guys at West Texas Ordnance, who have posted several articles on designing and hunting with the 25-7PRC. Given that I'm pretty much addicted to quarterbores after my .257 Ackley CZ 550FS that I had built a couple of years ago, this seemed like a natural choice. It is roughly ballistically equivalent to a .257Wby but throated and twisted to take advantage of the newer high-BC .25-cal projectiles from Sierra, Hornady and others.
The components for this project were:
Finished product:
It is a big, heavy s.o.b. but handles surprisingly well. A bit muzzle-heavy but that was kind of what I was going for.
Given I wanted the rifle both for steel ringing and hunting, I wanted to work up separate target and hunting loads. I knew I wanted to shoot Hammer's 127gr. HHT (published G7 BC of .262) for game and settled on the Hornady 134gr. ELD-M (G7 BC .325, G1 .645). Also picked up a box of Sierra's resurrection of the 131gr. Blackjack Ace to play around with (weirdly, no published BC but probably in the G7 .330 range?). There is no published load data for the 257PRC, so I relied on West Texas Ordnance's charges and COAL/CBTOs to guesstimate what I would need for the HHT and ELD-M. I also wanted to use a temp-stable powder. WTO listed H1000, Retumbo, RL26 and several Vihtavuoris. I chose the H1000 to start with due to Hammers' preference for a faster burning powder relative to other powders typically used in a given cartridge. My preferred brass is Lapua but they don't produce 7PRC. Figured I'd give ADG a shot, based on its reputation for stoutness (and knowing I was going to be playing with unknown pressures) and consistency. I then paired the ADG brass with Federal GM215M primers from a brick I had laying around.
My process was to lube the 7PRC brass inside and outside the neck with Imperial Sizing Die Wax (which smells vaguely of a stock barn?), then run the brass through a 25WSSM neck-sizing die. According to the WTO guys, this helps avoid the dreaded neck doughnut. I ran the neck-sized brass through my Hornady Ultrasonic case cleaner to remove and wax residue, then chamfered and deburred each case mouth. Finally, I cued up a couple of good podcasts episode and set to handpriming, trickling powder and seating bullets. Couple of dummy rounds that I cooked up to test cycling below:
Yesterday was the first chance I had to get out with the new rig. I don't want to burn this barrel any faster than strictly necessary, so took a box of .338-06 loads to test while the barrel cooled from my 257PRC ELD-M loads. Temp was about 70 degrees, clear skies, altitude approx. 6000ft. Since this is a true wildcat and I don't want any of y'all detaching your face from your body, I'm not going to post exact load data but I worked up in half-grain increments. Velocities measured using a LabRadar with a 3-D printed inertia trigger. Results were as follows:
257 PRC, 134gr. ELD-M, H1000, ADG brass, 3.210" COAL, 2.530" CBOL
I was disappointed with velocities but it is tough to be too down on fairly consistent single-digit SDs. The WTO guys claim to get 3238 with H1000 and the 135gr. Berger Hybrid, so I'm not sure why I'm down under 3100. I wasn't getting any real pressure signs, so could probably keep on the gas a good bit before I see any major issues. I might tinker with working up another 1-2 grains but accuracy and consistency is the primary concern with these loads. All of that being said, I'm hanging pretty close to Hodgdon's published load data for the 134gr. ELD-M and the .257Weatherby but with much, much slower burning powders (US 869, H50BMG, Retumbo).
**Also, I am a dummy and forgot to shoot the ELD-Ms for groups. Next time.
Today, I got out with the 127gr. Hammer HHT loads. I was pretty excited to try these out, as Hammers have consistently been both fast and accurate in several other rifles for me. The WTO guys have not loaded the 127gr. HHT but were getting 3250-3278 in a 22" barrel with the 128gr. Hammer Hunters and N570. Temp was about 50 degrees and drizzling rain. Again worked in .5gr. increments and this time remembered to shoot for accuracy, firing two 5-shot groups at each rung on the ladder.
257 PRC, 127gr. HHT, H1000, ADG brass, 3.070" COAL, 2.533" CBOL
I was aiming for 3350 with the Hammers but I am overall pretty pleased with 3327 and a 12.5 SD. I was starting to get some pressure signs (faint ejector mark below the ADG logo in photo 1 below, beginning to show cratering in photos 2). I probably have another .5-1.0 grains before I start getting weird with pressure but am inclined to leave the Hammers where they are. If I have a deer shrug off a 127gr. slug at 3327fps that I could have killed at 3350, so be it.
This is my first adventure in true wildcatting, so would really like to get some feedback from those of y'all that have tinkered off-book before. Any thoughts on going to a slower powder for the ELD-Ms? Any notes that could improve my process?
**Please work up your own load with this cartridge. My data may not work for your rifle and vice versa. Use at your own risk***
The components for this project were:
- Tikka T3X action;
- 24" Lilja No. 3 contour, 1:7 twist;
- Pure Precision Altitude stock;
- Mountain Tactical knurled bolt knob;
- RedSnake Tactical bottom metal (switched this over from my .338-06 build so that I could run Mountain Tactical billet mags on it);
- MDT LA box mags;
- Warne 20MOA Picatinny rail;
- Talley Tactical 30mm, medium height scope rings;
- Trijicon TenMile 3-18x44 scope; and
- DeadAir Nomad 30 with .264 endcap installed
Finished product:
It is a big, heavy s.o.b. but handles surprisingly well. A bit muzzle-heavy but that was kind of what I was going for.
Given I wanted the rifle both for steel ringing and hunting, I wanted to work up separate target and hunting loads. I knew I wanted to shoot Hammer's 127gr. HHT (published G7 BC of .262) for game and settled on the Hornady 134gr. ELD-M (G7 BC .325, G1 .645). Also picked up a box of Sierra's resurrection of the 131gr. Blackjack Ace to play around with (weirdly, no published BC but probably in the G7 .330 range?). There is no published load data for the 257PRC, so I relied on West Texas Ordnance's charges and COAL/CBTOs to guesstimate what I would need for the HHT and ELD-M. I also wanted to use a temp-stable powder. WTO listed H1000, Retumbo, RL26 and several Vihtavuoris. I chose the H1000 to start with due to Hammers' preference for a faster burning powder relative to other powders typically used in a given cartridge. My preferred brass is Lapua but they don't produce 7PRC. Figured I'd give ADG a shot, based on its reputation for stoutness (and knowing I was going to be playing with unknown pressures) and consistency. I then paired the ADG brass with Federal GM215M primers from a brick I had laying around.
My process was to lube the 7PRC brass inside and outside the neck with Imperial Sizing Die Wax (which smells vaguely of a stock barn?), then run the brass through a 25WSSM neck-sizing die. According to the WTO guys, this helps avoid the dreaded neck doughnut. I ran the neck-sized brass through my Hornady Ultrasonic case cleaner to remove and wax residue, then chamfered and deburred each case mouth. Finally, I cued up a couple of good podcasts episode and set to handpriming, trickling powder and seating bullets. Couple of dummy rounds that I cooked up to test cycling below:
Yesterday was the first chance I had to get out with the new rig. I don't want to burn this barrel any faster than strictly necessary, so took a box of .338-06 loads to test while the barrel cooled from my 257PRC ELD-M loads. Temp was about 70 degrees, clear skies, altitude approx. 6000ft. Since this is a true wildcat and I don't want any of y'all detaching your face from your body, I'm not going to post exact load data but I worked up in half-grain increments. Velocities measured using a LabRadar with a 3-D printed inertia trigger. Results were as follows:
257 PRC, 134gr. ELD-M, H1000, ADG brass, 3.210" COAL, 2.530" CBOL
| Average Velocity(fps) | Extreme Spread(fps) | Standard Deviation(fps) | |
| Load 1 | 2977 | 32 | 9.9 |
| Load 2 | 2997 | 24 | 8.3 |
| Load 3 | 3020 | 38 | 15.3 |
| Load 4 | 3047 | 26 | 9.7 |
| Load 5 | 3085 | 28 | 9.6 |
I was disappointed with velocities but it is tough to be too down on fairly consistent single-digit SDs. The WTO guys claim to get 3238 with H1000 and the 135gr. Berger Hybrid, so I'm not sure why I'm down under 3100. I wasn't getting any real pressure signs, so could probably keep on the gas a good bit before I see any major issues. I might tinker with working up another 1-2 grains but accuracy and consistency is the primary concern with these loads. All of that being said, I'm hanging pretty close to Hodgdon's published load data for the 134gr. ELD-M and the .257Weatherby but with much, much slower burning powders (US 869, H50BMG, Retumbo).
**Also, I am a dummy and forgot to shoot the ELD-Ms for groups. Next time.
Today, I got out with the 127gr. Hammer HHT loads. I was pretty excited to try these out, as Hammers have consistently been both fast and accurate in several other rifles for me. The WTO guys have not loaded the 127gr. HHT but were getting 3250-3278 in a 22" barrel with the 128gr. Hammer Hunters and N570. Temp was about 50 degrees and drizzling rain. Again worked in .5gr. increments and this time remembered to shoot for accuracy, firing two 5-shot groups at each rung on the ladder.
257 PRC, 127gr. HHT, H1000, ADG brass, 3.070" COAL, 2.533" CBOL
| Average Velocity(fps) | Extreme Spread(fps) | Standard Deviation(fps) | Best 5-shot/3-shot group | |
| Load 1 | 3171 | 61 | 20 | .537/.274 |
| Load 2 | 3218 | 27 | 7.5 | .623/.477 |
| Load 3 | 3259 | 62 | 17.9 | .956/.277 |
| Load 4 | 3290 | 41 | 12.3 | .904/.399 |
| Load 5 | 3327 | 44 | 12.5 (final 5 rounds 2.3) | .503/.183 (!!!!!) |
I was aiming for 3350 with the Hammers but I am overall pretty pleased with 3327 and a 12.5 SD. I was starting to get some pressure signs (faint ejector mark below the ADG logo in photo 1 below, beginning to show cratering in photos 2). I probably have another .5-1.0 grains before I start getting weird with pressure but am inclined to leave the Hammers where they are. If I have a deer shrug off a 127gr. slug at 3327fps that I could have killed at 3350, so be it.
This is my first adventure in true wildcatting, so would really like to get some feedback from those of y'all that have tinkered off-book before. Any thoughts on going to a slower powder for the ELD-Ms? Any notes that could improve my process?
**Please work up your own load with this cartridge. My data may not work for your rifle and vice versa. Use at your own risk***
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