AS I understand it years ago many 375 H&Hs were converted 70375 Weatherby for 100 fps gain in velocity and some improvment in ballistics. The question is this: were that to done what would happen when I fire 375 H&H ammo as would be most often, would there be any degredation in ballistics or velocity of whatever...? I understand I would be fireforming the cases to be reloaded as 375
Weatherbys. Any other implications...? and who would do this work...? Thanks in advamce.

It seems that this conversion is a fairly common one for the 375 H&H. As far as firing 375 H&H in the Weatherby chamber? No problem, though you will get some velocity loss. Other than that, I do not know of any other associated problems.

My Late brother had a beautiful 375 H&H ( pre 64 model 70) that had been converted to 375 WBY. It was very accurate but because he had also put a very light stock on it, it recoiled viciously. His PH, Clive Eaton, would routinely hide his 375 WBY ammo so that David would have to borrow Clive's 375 H&H ammo and somewhat tame the beast. The rifle shot the 375 H&H quite well and sufferred no ill effects from the swap. I now have the gun. It is a beauty but is a handful to shoot even with 375 H&H. I'm planning to restock the rifle with something a little more substantial so that it can soak up some of the recoil. I have another pre 64 375 H&H with a standard stock and it is very comfortable to shoot. If I get the weight of David's rifle up to that of mine I think that I'll be taking back to Africa on my next hunt.

It would function just like an Ackley Improved. The round headspaces on the rim. The H&H case expands to fill the chamber. A H&H round in a 375 Wby will give you a little lower velocity and pressure than it would in a normal H&H chamber because the brass and gas has to expand to fill the larger chamber.

The velosity drop in my 375AI is only 10fps when fire forming new H&H brass

There are a few other aspects that you may want to consider. If you are using a Brno or a CZ you will probably have a much longer magazine box than say a Winchester Model 70. I think one of the attractive things about rechambering to 375 Weatherby is the ability to use heavier extra long bullets (say the Rhino 380 grains), seating them way out if box and freebore permit it, and getting some really good velocities with heavy bullets. But you should check magazine box dimensions and freebore and see if any modifications might also be needed to get the most from the conversion.

I have read (meaning I have no idea if it is true) that firing full power H&H loads in the Weatherby chamber may reduce brass life. If it's only for fireforming than you may want to handload some lower power cartridges.

Sorry, forgot to mention the Gun is a Ruger Mark 2.

Not worth the effort...

hornady is loading 375HH to 375 Ackley velocities with factory loads..

you'll be in it at least 500 bucks, gunsmithing, dies, reamer, for about 75 FPS net if you load 375 weatherby pressure, you are still in the ~2650-2700 fps with a 300 grain bullet.

and you get a WHOPPING 10 grains more room.. or about 50 bucks a grain.

jeffe

Had a 375 Ackly for a couple of years, theres a lot more than 75 fps to be gained. That said I'm about to take apart a 300 H&H mod 70 and make a 375 H&H.

Let me rephrase that last post. I certainly don't want to come across as confrontational. My particular custom Sako with 22" .375 Ackly chamber would do 2800+ fps no problem.Anybody need a very nice pre-64 Westerner style stock in totaly original condition, no bedding factory butt plate, also 300 H&H barrel throat and rifleing look new blueing almost perfect. One very small mark 1" from muzzle.

MTM,
nah, not confrontational.. though if you load the 375HH to the same pressure, the difference is about 75 fps.. hornady gets 2705 with a 300 grain bullet in the HH in their heavy mag. so let's call it 100fps from your 2800+ compared to the 2700+

or, looking at the case capacity
10grs more in the 375webby vs HH. so take 40% OF that, and express in percent, a 1, and multiply that by parent case velocities.. and that's about the most AT THE SAME PRESSURE that you can get from an improved round...
or 1.04*2500=2600fps ..

load BOTH hotter, and you get better results

jeffe

What ever floats your boat, but I simply can't see where the gain is, when destroying the collector value of a factory chambered mod 70 to gain an un-needed 100 fps, or to rebarrel a factory 300H&H mod 70 to make it into a 375H&H! I think it would be better to sell me the 300H&H, and buy a 375H&H, and forget the Wby chambering, which will kill no better than the old 1912 H&H, and spend the $500 bucks for a lot of H&H ammo, or another trophy fee!

MacD37,
Just to be clear I wouldn't rechamber a factory old mod. 70. My Ackly was a rebarreled 338. If I could find a factory pre-64 375 for a reasonable price I'd sell the 300. Around here old 375s cost both arms and a leg. Plus I'd just end up chopping 3" off the barrel thus destroying the value anyway. I've got a new Safari Classic barrel that I'm going to shorten and remove the extra lug. It will be a standard H&H. Just have to decide on stock.

Well said MacD37, I totaly agree with you. You just cannot beat the old 375 H&H

quote:

Originally posted by jeffeosso:
you'll be in it at least 500 bucks, gunsmithing, dies, reamer, for about 75 FPS net if you load 375 weatherby pressure, you are still in the ~2650-2700 fps with a 300 grain bullet.

and you get a WHOPPING 10 grains more room.. or about 50 bucks a grain.

jeffe

Can't say as I'd go cutting on a pre-64 70 for this project either. BUT......I just had it done on an A-Bolt Stainless Stalker. Got the trigger done, chamber cut, reciever and bases tapped out for the bigger screw and scope mounted/bore-sighted for $265. I got my dies NIB on eBay for under $60. I can supply contact information for my smith. If anyone wishes to have it, shoot me a PM.

quote:

you'll be in it at least 500 bucks, gunsmithing, dies, reamer, for about 75 FPS net if you load 375 weatherby pressure, you are still in the ~2650-2700 fps with a 300 grain bullet.

Maybe not quite $500 but not far off.

I truly scratch my head when the idea of the .375 Weatherby comes up.....I can't for the life of me get excited about the loss of ammo availability and the trade off of nearly 100'/sec....

Vapodog: as I understand it, what you claim is NOT correct. I would have both 375 H&H factory ammo available AND either handloaded 375 Wby or purchased Wby ammo available. Sort of like shooting 44 Spcls in a 44 magnum. Can do either or both.
Just seemed like a good idea and one that I had seen touted in the distant past. Don't want a 378 Wby. Am very happy with the 375 H&H just thought it might be good insurance for some future endeavor. So while I have the gun out being worked on,,,,,,,,

On one hand you will have fun with it and thats what guns can be for. Of course it will not matter a whole lot one way or the other once the bullet leaves the barrel.

Some things to consider are that the expansion webs on the 375 H&H brass will be weakened in fireforming and have a short case life and questionable reliablity.

Also if they are to be taken to Africa or wherever there is some mumbo jumbo about having the same headstamp on the case as the gun.

The Weatherby cartridge is standard sort of at least. Don't make the mistake I did of getting a 375 AI chamber. I am stuck with that.

For what it's going to cost you in money you can be half way there to getting a 416 also and having two guns.

With the heavier bullets of 300 to 350 grains, one can get 200 to 250 fps advantage over the .375 H&H. This comes from the 10 to 15% heavier charges of slower powders that you can move into with the .375 Wby (depending on some mild compression, not heavily compressed "Secret BS"). Some extra advantage shows up there.

100 to 150 fps advantage with the 235 to 270 grainers hardly makes it worth it in the .375 Wby.

.375 H&H "Heavy Magnum" and "High Energy" factory load "Secret BS" are not as good as they claim. Expect 2600 fps if they claim 2700 fps, and lousy accuracy from heavily compressed "Secret BS" loads that you cannot duplicate by handloading.

My .375 Wby's will send the factory .375 H&H ammo downrange with only 100 to 125 fps loss of velocity. This turns the 300 grain factory ammo into "Doctari" Loads at 2400 fps. Extra lethal with any old factory bullet.

The factory .375 Weatherby ammo is easy to duplicate in velocity and improve in accuracy, but one had best stop when he gets to these velocities with 300 grain premium bullets:

24" barrel: 2750 fps
26" barrel: 2800 fps

That is about all a .375 RUM will do with the factory stuff also.

With the .375 Wby chambered rifle, your .375 H&H factory ammo will arrive on target only 2 or 3 inches lower at 100 yards than the full power .375 Wby loads. That is pretty handy in a pinch, when you know your rifle and you know your ammo.

Hal Waugh's Big Nan was a .375 Wby that was proven over several decades of guide service in Alaska bear country.

You just can't beat a .375 Wby for versatility and real gain from a simple rechamber. Stock up on the properly headstamped brass while it is still plentiful again after all these years.

The 2001 version chamber is a whole lot better than the 1949 version that had excessive throat.

The .375 Wby just keeps getting better.