When my MK V was a cannon ,the heavy recoil and atomic muzzle blast wasn't worth the poor accuracy( Accustomed to varmint rifle accuracy) . Couldn't seem to find a buyer ,so found a WBY authorized smith and had him reduce it to 257 WBY . Bought a 10"twist Bartlein 26" bbl Rem Varmint contour.Its now a heavy rifle and even with the brake it kicks,I'd say as much as my braked 7mm WSM . Regardless it seems like it only took 9 rounds to find a 1/2 MOA load . 69grs of IMR 7828 SSC behind a 100 gr Sierra SPBT . 3 shots with a minute between shots and that heavy bbl is hot,( Hot day in NV desert though)
338-370 WBY reduced to 257 WBY Mag
- Thread starter Ironworker
- Start date
Kurz
Silver $$ Contributor
I guess I'm reading that this was a .338-378 WBY with a 0.590 rim?
Then you re-barreled and re-chambered to .257 WBY which uses a 0.532 rim?
Did your 'smith replace the bolt or modify your bolt to work with the smaller bolt face?
I shoot both the .30-378 and .338-378 WBY and like them for the purposes I have need of. But there is no replacing the .257 WBY as the king of .25 caliber rifle cartridges. The rifle I'm using currently is set up to shoot the 131 gr. Blackjack bullets.
typo yes 338-378 . Weatherby sold my gunsmith a new Bolt with 0.532 rim...... What velocity are you getting out of yours shooting the 131gr Black Jack bullets ? Is it a 1-7" twist ?.
Kurz
Silver $$ Contributor
Excellent! I'm glad they cooperated with your 'smith. Sometimes corporations can get a little sticky about projects like this.
~ 3250 and a pinch more when I push it a little. No, 1:7.25", not that it's a big deal.
Do you have a muzzle brake on yours,if so what brand type ? I had an old Vias laying around ,I had him install that. Maybe I should've thought twice ?
Kurz
Silver $$ Contributor
While I am usually a fan of muzzle brakes, this one is a hunting rifle so I am running it without a brake at all. The muzzle is threaded but capped if I change my mind.
I blank out my own here in the shop so I don't have to keep a specific inventory by thread size. The design is a sort of standard 3-port quick discharge style. For larger cartridges and bigger diameter bullets I will use the very aggressive Cadex MX-1 brake:
I blank out my own here in the shop so I don't have to keep a specific inventory by thread size. The design is a sort of standard 3-port quick discharge style. For larger cartridges and bigger diameter bullets I will use the very aggressive Cadex MX-1 brake:
Yeah, hh , hh, that would be cool !Whoa! For a minute there, I thought you made it a 257-378.
did you try any us869 ? Or lrt powder ?
Kurz
Silver $$ Contributor
In which cartridge(s)?
US869 works well in the .30-378 with the 198 Flatlines but I haven't worked with it in the .338-378 yet. It will NOT function in the .257 Weatherby by my calculations. Not near enough case capacity.
it will and does, it will fill the case very well. The speed with 88 bibs is not as high as other powder's, but it is very accurate. I use the 88 bib with 85 grains us869= 3400 fps. This load is not a high pressure load at all and it makes low one's- low two's depending on the day. Also these two powder's would be even better suited for 131 b.j. and i suspect they would provide great speed with those heavy bullet's compared to others.
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69grs of IMR 7828 SSC will be the load until my box of 100 gr Sierra SBT runs out.
Kurz
Silver $$ Contributor
My brass, fireformed in my chamber, holds about 84.2 grains of H2O to the top of the neck. I would have to vibrate your load of 85 grains heavily for a bit in order to get that load to settle enough to seat a bullet without the potential of pushing the bullet out of the neck.
Even your 'load' will not generate enough pressure to show any signs based on the information supplied. I don't shoot 88 BIB or anything else in that weight class. I've been shooting nothing but the 131BJ, 128HH, 121HH, 115Ber and the 103HH with this chamber. When I tried the US869 with the 131 Blackjack, the velocity was unacceptably low due to lack of case capacity and a desire to avoid the lack of gain by vibrating the load. There are powders much better suited to this combination which I will continue to use especially considering the bullet design is for longer range use. But that's what makes America great! You can have your opinion and I can have mine!
Preposterous i say ! Ha,I didn't pull this information from thin air, Ha , i read the opinion of Accurate powder company. They claim 8700 powder is the best in 257 weatherby. 8700 is discontinued but us869 and lrt are very similar.( Accurate powders) load data shows 90 grains of 8700 as a max load for 87 grain bullet . and 90 grains for the 100 grain bullet . my first test with 88 bib was 90 grains of us869. Accuracy was 3/4" so my next test was 85 grains us869 and hit the jackpot. First group was in the zeros ! Wow! 3400 fps is not to shabby. I know that as you go up in bullet weight this powder will do better as far as velocity is concerned. That's what it's made for, pushing heavy bullet's to top speed. Ps. 90 grains fit in my case, with room to seat bullet- it was full but 85 was no problem with no vibration needed. I don't know how much would be max load for 131 bj. But i would guess about 80+ . you said you tried us869 can i ask what the load was ?My brass, fireformed in my chamber, holds about 84.2 grains of H2O to the top of the neck. I would have to vibrate your load of 85 grains heavily for a bit in order to get that load to settle enough to seat a bullet without the potential of pushing the bullet out of the neck.
But that's what makes America great! You can have your opinion and I can have mine!
Kurz
Silver $$ Contributor
1) 8700 doesn't even exist any more. It was discontinued quite a while ago so unless folks have some stashed away, the information is for conversation only and essentially useless.
2) We were discussing the Blackjack 131 bullet not some stubby little bullet short seated in a big case.
3) Your points are just argumentative and a waste of time based on the original thread.
4) If you want to shoot light bullets at slow velocities, enjoy yourself.
I'm done wasting my time with you and information.
2) We were discussing the Blackjack 131 bullet not some stubby little bullet short seated in a big case.
3) Your points are just argumentative and a waste of time based on the original thread.
4) If you want to shoot light bullets at slow velocities, enjoy yourself.
I'm done wasting my time with you and information.
No your not, i say when you're dun. 8700 is discontinued but us869 is as close to identical as you could get. It is better than 8700. And it's better than lrt for pushing long heavy bullet's in overbore magnums. And if you look at the load data it shows 8700 makes the highest speed with heavy bullet's in the 257 weatherby/ thus us869 will also! So if a person wants both high velocity and excellent accuracy a person would use us869. The only reason i use us869 with 88 bibs is because of the incredible accuracy. So let me recap, with light bullet's us869 does not make highest speed but with heavy bullet's it does make the highest speed.
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257Blackjack
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Customers are running 257 WBY with 1:8" twist and a few with 1:7's up to 3420+ fps in 24-26".
25 SAUM will run 3320-3400 fps in 26-30" and the WBY will provide a bit more than that.
They are shockingly flat and hard hitting to 1320-1760 yards on steel. I watched a 25 SAUM earn 2nd place in the Q Creek ELR Open Division out of 200 shooters a few weeks ago. I brushed off the 25 SAUM as a bit too hot but after seeing how it handled wind at long ranges and competed against much larger cartridges 25 SAUM, PRC, and WBY are back on the list for chamber jobs.
25 SAUM will run 3320-3400 fps in 26-30" and the WBY will provide a bit more than that.
They are shockingly flat and hard hitting to 1320-1760 yards on steel. I watched a 25 SAUM earn 2nd place in the Q Creek ELR Open Division out of 200 shooters a few weeks ago. I brushed off the 25 SAUM as a bit too hot but after seeing how it handled wind at long ranges and competed against much larger cartridges 25 SAUM, PRC, and WBY are back on the list for chamber jobs.
Yup I made a 6.5 x460 Weatherby. It was shortened a bit and had 40 deg shoulder . This was in the early eighties, barrel life was about 1000 before it was total toast , 600 rounds and you could figure 3"" of bore was gator checked .Whoa! For a minute there, I thought you made it a 257-378.
Still have all the reamers .
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