Best powders and loads for 300 WBY Mag and 257 WBY Mag?

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glen8338

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Just purchased Two WBY Mark V Ultra Mark, One in 300 and the other in 257. The factory ammo from Norma for the 300 was way too hot- pressure signs and velocities of 3325 fps for the 180 gr Spitzer, while the 257 factory 100 gr Spire Point was averaging around 3750 fps. No observable pressure signs but I thought that is faster than their claim. I pulled the bullets of the 300 WBY Mag cartridges and proceeded to load with H4831SC and RL 19. After working up loads I found 79.5 gr of RL19 gave me an average velocity of 2991 fps and no pressure signs. haven't started reloading for the 257. Any experience loading for these two rounds would be appreciated.

The reason I purchased these two as I am a left handed and left eyed shooter and I have always wanted a Weatherby? thanks.
 
I've got a 300.
I've had really good success with IMR 7828 and nosler accubonds
I've also had very poor results with nosler partitions and won't buy them again.

I found R/P brass for the weatherby is junk and splits necks, quite often on the first firing from factory rounds.
 
Thanks for the info. IMR 7828 is listed in the reloading manuals as a reasonable powder. Is it the 180 Accubonds you were loading? What weight of charge? These are Norma cases and I've heard that they are the best. Did you use a magnum primer?
 
Don't have a .300 Wby, but I'm really liking Hodgdon's Retumbo and Berger 115 VLD bullets in my .257 Wby.
Hodgdon's H-1000 works pretty good as well.

I'm using Hornady brass.
 
7828 in both of them if you want to keep it simple. My .300 is good for 3150 fps with the max loads in the Nosler book (24 " barrel) and 180 Hornady Interlocks and Partitions. It also shoots the cheapest spire point factory loads; all three of those would meet the 1" Vanguard accuracy warranty. For some reason it wont shoot a 180 boat-tail anything worth a crap, but is showing promise with the 200 grain Accubond.

I've had good luck with IMR 4831 in 3 different .257s with 100 grain Ballistic tips and TSXs. Max load in the Nosler book.
 
To obtain maximum velocity with the heaviest bullets, you will need to start with the powders mentioned (IMR7828, H1000 and Retumbo) and include others that are slower yet - Re25, Re33, Re50 and the new IMR7977 (if/when you can find them) and US869.

You can't get enough of a slow enough powder into the 300 Wby to exceed about 3200 fps with an 180 gr bullet, and in the 257 Wby about 3700 fps with a 100 gr bullet unless you exceed SAAMI pressures.
 
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glen8338 said:
Thanks for the info. IMR 7828 is listed in the reloading manuals as a reasonable powder. Is it the 180 Accubonds you were loading? What weight of charge? These are Norma cases and I've heard that they are the best. Did you use a magnum primer?
Click to expand...

Norma makes weatherby headstamped brass. They do have more volume than the R/P and the R/P will run higher pressures.
I've got some hornady now, but haven't used it yet.

One very interesting I found was that I got a good 100 fps better velocity with the accubonds over the partitions with the same load, brass, primer.
I used CCI magnum and Fed 215 with the 215 giving better S/D and group.

Start at about 81 or 82 gr of 7828 and work up until you're over 3200 fps with a fed 215 and a 180gr bullet.
 
Thanks for all the info! Must get some IMR 7828 and Retumbo. Thank you to the other Weatherby guys and gals
 
Just purchased some IMR 7828, but Cabelas in Edmonton did not have any Retumba so will have to wait to try this one. Kinda sounds like both the 257 and 300 like IMR 7828. Can't wait to try! thanks all!
 
I have tried IMR 7828 in both and it works good! Right around 3150 fps with 180 Accubonds, Fed MAG 215 and 83.5 g of 7828. Tried the 110 g Hornady Interbond with 72 g of 7828. Still want to try a load for 120 g bullet. Accurate loads and will tweak them a bit more. Thanks to all who gave info!
 
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