Long Range Hunting Online Magazine

Go Back   Long Range Hunting Online Magazine > Rifles, Reloading, Optics, Equipment > Reloading

Reloading Techniques For Reloading


.375 H&H Fireform to .375 WBY?

LinkBack Thread Tools Display Modes
Old 12-27-2013, 09:26 AM
Platinum Member
Join Date: Dec 2009
Location: 4422′44″N 1082′35″W
Posts: 3,814
Re: .375 H&H Fireform to .375 WBY?

I guess I spoke without knowing my facts, I just looked up the specs on the H&H and the WBY and say the .001 difference and in my mind it was close but wouldnt work in all instances so to me not really an option. I didnt realize it was common practice. I dont ever plan to own a 375 wby but if I ever do thats good to know. As for a rum reamer cleaning up a H&H hole I really dont know ^^someone up there said it would so I assume he is right...seems like it would.

Anything less than overkill is underachievement!

" Real elk guns start with the number 3 or bigger and blow two holes, one in and one out." - My Dad
Reply With Quote
Old 12-27-2013, 03:29 PM
Bronze Member
Join Date: Jan 2011
Posts: 67
Re: .375 H&H Fireform to .375 WBY?

The OP hasn't been back, but he needs to clarify if he's talking about the .375 Weatherby as indicated in his title, or the .378 Weatherby as indicated in the body of the post. They're two completely different rounds. The .375 Weatherby is indeed a blown out .375 H&H case and can easily be fireformed from .375 H&H brass. The .378 Weatherby is a larger case, being the .460 Weatherby or .416 Weatherby case necked down to .375. The .378, .416, and .460 Weatherby are all based upon a .416 Rigby case with a belt added to it, and the .375 H&H case will not work for them.
Reply With Quote
Old 12-31-2013, 03:51 PM
Junior Member
Join Date: Dec 2013
Posts: 15
Re: .375 H&H Fireform to .375 WBY?

Info so far greatly appreciated.

What started as a typo turned out to be a good thing. The original intent was to ask about fireforming a .375 to a .378, but the actual situation was about rechambering a .375 H&H to .378 and using cheap brass. If it is possible to get .375 RUM velocities from a .375 (not .378) Weatherby, that would be really nice. Obviously, a rechamber that increased headspace would not be possible.
Reply With Quote
Old 12-31-2013, 06:55 PM
Bronze Member
Join Date: Jan 2011
Posts: 67
Re: .375 H&H Fireform to .375 WBY?

You can't fireform .375 H&H to .378 weatherby, they've got different case head sizes and it won't work. You can't even rechamber most .375 H&H rifles to .378 weatherby because the actions physically aren't big enough to handle the huge weatherby case. The only real exception to that is a weatherby MKV action, it's big enough to handle the .378 weatherby and I believe a few were chambered in .375 H&H so those could be rechamered if you enlarge the bolt face too.

Now the .375 weatherby is a different story, it's merely an "improved" version of the H&H with a lot of the body taper blown out and the shoulder fireformed. Since a belted magnum headspaces on the belt instead of the shoulder it's a simple matter of having a gunsmith run a reamer into the H&H chamber and cutting it to weatherby dimensions. As long as he doesn't move the belt forward the headspace remains the same. Since they both headspace on the belt you can fire .375 H&H ammo in a .375 weatherby chamber and it'll work fine. When the brass comes out of the chamber it'll be fireformed to weatherby dimensions.

A .375 weatherby gives quite a bit extra case capacity over the H&H so it's good for about 250 fps more, but it's still not quite got the volume of a .375 RUM so it's not going to be quite as fast loaded to similar pressures. It's still an excellent round and I'd prefer it to the RUM. There comes a point with me where the recoil exceeds my comfort zone and I although I haven't fired a .375 RUM I expect it's past that level.
Reply With Quote
Old 12-31-2013, 09:28 PM
Silver Member
Join Date: Feb 2008
Posts: 393
Re: .375 H&H Fireform to .375 WBY?

Although what you say about the case capacity of the RUM case is true, my own testing showed only a 20-30fps difference between it and the 375 Weatherby with factory ammo, I was surprised to say the least. We shot them side by side over the same chrony and the RUM was a LOT slower than I expected, even the owner of the rifle was totally surprised.
With my handloads and a max charge, I have been able to consistently achieve 2850fps with 300gr Woodleigh PP's, which is right up at listed RUM velocities in most loading manuals.
I think this is due to the fact that the Weatherby case seems to be quite efficient in powder to velocity ratio, which I noted at the get go when I first started loading for it, this seems to stem from the 1/2" of freebore, where the velocity rises quite well and pressure seems to be quite linear with no excessive pressure excursions.
I agree, the recoil is quite a step up from the standard H+H round, it's a lot sharper and gets your attention, but is not excessive, it's not as harsh as my 458Lott!

Reply With Quote
Old 01-02-2014, 12:35 AM
Silver Member
Join Date: Jul 2012
Location: Washington State
Posts: 448
Re: .375 H&H Fireform to .375 WBY?

The order of case capacity is: H&H, Ruger, 375 Weatherby, RUM, 378 Weatherby.

One parameter that is not measurable for most shooters is pressure. Most hand loads are high pressure and most factory loads are far from it. Most recent experience with factory loads (most of my guns never see factory ammo) is with a friend's 7mm RemMag. Hornady Superformance 162 gr SST was closest to claimed velocity (-22 fps and the barrel was 2" shorter than factory) and the Remington Corelock was the least (2700fps vs. 3000fps claimed). Factory ammo not performing up to par is S.O.P. That's why I recommend to beginners to get a chronograph as their first purchase. Apples to apples has both cartridges at the same pressure.

When two same caliber cartridges are compared the higher capacity case wins. Short fat cases don't deliver higher velocities (as proved by P.O.Ackley) but they are MUCH more consistent. Fat cases deliver very low shot to shot variations. But Weatherby's claim of venturi effect has never been proven. It is based on the PMVF wildcats of the 30's.

Start pouring powder into both the RUM and 375 Weatherby and when the primers start cratering the RUM will be burning more powder and developing more velocity. To really do this right you would use the same barrel and rechamber.

Just the history of wildcaters and reloaders pushing the limits speaking here. If there was a magical case shape someone would have found it and the ammo companies would have made them rich with licensing fees.

Reply With Quote
Old 01-02-2014, 04:36 PM
Junior Member
Join Date: Dec 2013
Posts: 15
Re: .375 H&H Fireform to .375 WBY?

Looking at the .375 Weatherby, it appears to have a shorter neck and presumably more freebore than the H&H. Will this have an effect on accuracy and/or velocity?
Reply With Quote


Thread Tools
Display Modes

Current Poll
Do you watch outdoor shows live or by recording them?
Always recorded - 13.35%
110 Votes
Mostly recorded - 24.15%
199 Votes
Sometimes recorded - 14.44%
119 Votes
Rarely or never recorded - 48.06%
396 Votes
Total Votes: 824
You may not vote on this poll.

All times are GMT -5. The time now is 11:00 AM.

Powered by vBulletin ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Management Powered by vBadvanced CMPS
All content ©2010-2014 Long Range Hunting, LLC