Mashburn Magnums

[VLGuns]

Hi folks, new to this forum. Briefly about me, I am a gunsmith, have been for almost 40 years, started as an apprentice at Cleveland Custom Gunshop. Just had a customer bring me a Mashburn rifle for a total refinish.

My question is, it is stamped 300 short magnum mashburn. He gave me a fire formed case headstamped .375 H&H.
He has a few boxes of ammo and all are headstamped .375 H&H. I know Art Mashburn based his short Mags on the 300 H&H case and both the 300 and 375 have the same head dia. of .532. Just wondering if there is anyone out there who can give me info on this cartridge? Did he use 375 cases because he was out of 300's? Or is this a different caliber altogether? He wants a set of reloading dies and RCBS has dimensions for a 300 Mashburn mag. but nothing for 300 short mag mashburn. I will do a chamber cast to confirm that his fire formed case (from Mashburn) is the same. I am looking for info for both myself and my customer. ANY help is appreciated. E-Mail me at guns@viktorslegacy.com or through my website viktorslegacy.com Thanks for anybodies help.

 

[aixenmemphis]

From page 435 of P.O. Ackley's Handbook For Shooters & Reloaders, Volume I:

"This is a true short Magnum made by necking down and shortening regular .300 H&H cases. Like all Mashburn cartridges, it has the 30-degree shoulder. Although slightly longer than the No. 2 Ackley Short Magnum, it is very similar to that case. The overall length of the Short .300 Mashburn (2.530) is less than the 7mm Mashburn Magnum, making it a much better balanced cartridge than the 6.5, .270, and 7mm Mashburn Magnums. The capacity of the short .300 Mashburn is about the same as the standard .300 H&H, but it is a much better designed cartridge foe use with modern American powders."

 

[VLGuns]

Thanks for the info. I checked the case length, it is 2.545 with a .375 long neck. .015 seems a bit much to grow for a once fired, fire formed case. I know Art Mashburn was the one who formed the case as it has a deep filed cut in the case rim and no primer. Art did this as a "proof" test and gave the customer the fired case marked (if you will) as evidence. So although P.O. Ackley has the case listed as being 2.530 long, I'm still not 100% convinced that this shortened & necked 375 H&H case is a 300 Mashburn short mag. Slap me if I'm being too cautious.

 

[aixenmemphis]

I have found a lot of info that people in the past have used 338 win mag brass as their starting point