7 Mashburn H4895 Fire Forming

[joelkdouglas]

I've been pretty consistently making small amounts of 7 Mashburn brass (from original case 300 Win Mag), anticipating a new 7 Mashburn this late spring/summer. The Mashburn on the way will add to the already one I have.

I have also been wondering how to fire form brass best. The best way to date is 65 grains IMR4350 with a 139 Hornady bullet. I don't hunt with this load though, so I wondered if I could fire form cheaper. I've also tried cream of wheat method and I don't care for it.

I got looking into H4895 Youth loads. With a 130-grain bullet Hodgdon lists 41 grains for a 7 Rem Mag and 45 grains for a 300 Win Mag. I guessed the Mashburn to be between them in case capacity and near the Win Mag. I loaded up 15 cases of Mashburn with 130 Speer bullets and 44 grains H4895 in Winchester cases. Results were pretty good! Recoil is very mild, and headspace measured from the shoulder datum to the cartridge base (I realize the case headspaces on the belt and not the shoulder):

H4895 load: 2.181 inches from cartridge base to shoulder datum
IMR4350 load: 2.183 inches
Full charge loads after three firings: 2.187 inches

The good thing about the H4895 load is only uses 2/3 of the powder, and uses 130 grain Speer bullets. All told the bullets are $10 cheaper for 100 bullets, and cheaper amount of powder. And no recoil, which is pretty nice!

 

[mrandrew]

I use 13 grains of tote group with a case full of corn cob media. Point it up in the air and poof. No recoil and a fire formed case.

 

[joelkdouglas]

Took some more measurements this morning after having some time.

The H4895 youth load brass has tighter necks (necks didn’t expand as much) and the concentricity of the fired brass is pretty terrible! I’m guessing the youth loads don’t generate enough pressure to really make the brass expand enough.

Maybe I’ll load some up with 50 grains and continue the experiment until I’m out of that lb of powder.


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[Dwh7271]

Don’t know if this helps but what I do (along with false shoulders) is load toward the top end of the standard loading. Having no standard in the Mashburn, i talked to Scotty and used the 4350 load.

 

[truck driver]

Not a Masburn but when fire forming 35Whelen AI I use a top 35 Whelen charge with light bullets and it fire forms the case to match my AI chamber. I get perfect cases every time.

 

[SJB358]

Since the Mashburn isn’t blowing a ton of taper out of the cases and they are formed real well after they come out of the form and trim dies I’d almost wonder if you couldn’t use a regular old hunting load in them. Maybe they won’t be quite as guilt edge accurate but That’s about all Gene Simillion does with the Mashburn loads he works up.

Those RWS cases are TOUGH. My 65 grains of IMR4350 WILL NOT fully form an RWS case. I get blackened cases since they aren’t sealing. Still takes one full power shot to make them perfect.

I like the idea of the youth loads though. Probably worth exploring. Maybe H4895 or similar plain old 7 Rem loads with 130’s would work.

I’ll be watching as you keep bumping up the charge weights.

The 65 grains of 4350 with a 140 AccuBond went 3220 in my old rifle and man, it was really accurate. I always thought that would be a slick deer or even elk combo if a guy didn’t have time to go through a full FF, ream and load procedure. Haven’t tried it in the new gun but may give it a shot. Might even try with some plain old 150’s as well.