In comparing the reamer specs it appears to me that the Weatherby has a slightly shorter base to shoulder dimention than the H&H chamber .



So , I guess my question is , does a .375 Weatherby reamer clean out a .375 H&H chamber , without setting back the barrel ? Or , has anyone had experience with this conversion ?

Interesting question.

I may be wrong but I thought the original .375 weatherby was nothing more than a .375 Ackley improvement. One of the original sales points was you could shoot factory .375 ammo in it.

Base to shoulder is 2.431". To neck is 2.506". You have to make sure you get the right reamer.

375 Weatherby is NOTHING MORE than an improved 375 H&H.
No difference in head dimension or overall length.
In fact, you may shoot 375 H&H ammo in it to fire-form.
The downside is that the 375 Weatherby is an obsolete caliber, whereas 375 H&H is still a very popular cartride.
I personally own a 375 H&H myself, and boy is it pleasant to shoot. With lead Bear-Creek Cast Bullets, the recoil is just a little push on the shoulder.
So, if you are considering rechambering, even as a gunsmith, I would recommend you leave it alone.
Even if it is a mild improvement, I do not think that it will be worth the money and/or time you put into it.

-Spencer

According to Dr. Howell's book,



.375 H&H shoulder starts at 2.4122" from base and ends at 2.4976" from base, total length of shoulder = .0854"



.375 Weatherby shoulder starts at 2.3960" from base and ends at 2.5560" from base, total length of shoulder = .1600"



So, yes, shoulder begins at a point a little shorter than the .375 H&H, but it ends at a point a ittle farther out than does the H&H. In the meantime, the diameter at the shoulder has gone from 0.4478" at the beinning of the shoulder in the H&H to .4920" in the Weatherby (.0442"bigger) and from .4020" at the end of the shoulder in the H&H to .4000" in the Weatherby (.0020" smaller).



In addition, the shoulder is double radiused in the Weatherby, rather than beginning it's reduction in diameter abruptly.



So, all in all, unless the H&H chamber is oversized, the shoulder area should just clean up when rechambered, but the neck area should not.



Difference in total capacity is 8 grains of water in favor of the Weatherby.



Using a powder with a specific gravity of .9, that should translate to an increase in powder capacity of 7.2 grains for the Weatherby. That's an increase in powder capacity of about 6%, so should yield a velocity increase of about 1-1/2 %, IF one accepts the generalized rule of velocity increasing about 1/4 of the powder capacity increase.



Ken used SAAMI maximum chamber dimensions for the H&H, and Weatherby's maximum dimensions for the Weatherby chamber.



AC

AC,

Where the....1/4.....1.5% falls over with the 375 Improveds is with heavy bullets. In the 375 H&H the 4064 burn rates are too fast and the 4350 burn rates are too slow and especially with longer pointed bullets. If equally suitable powders were available then of course the....1/4.....1.5%...is good value

One of the posters on this forum, John S, recently saw that happening with his 375 H&H and his Echols made 375 Wby with bullets from 250 grain through to 300 grain.

Mike

Mike.....do you recall if John mentioned how his Weatherby did with the 250 to 270 grainers ?

Actually , the figures I've seen , and also my own guesstimates with empty cases , show right at a 10% gain in capacity for the Weatherby case . Like you , I figure the bigger case will hold just enough more of the slower powders to make a bit more difference than just the per cent of capacity would indicate . Also , this particular rifle likes to stretch the cases alot when you push it a bit........the chamber seems to be plenty large........and hopefully the sharper shouldered case would help that out .

I've had both and while I like to play around with odd-ball cartidges this is one I will not bother with again. It does not turn the H&H into a "reach out and touch something" round. For that get a 375 RUM or 378 Weatherby. 300 gr 375 bullets at normal hunting ranges do their best work between 2300 & 2400 fps anyway.

Alberta,



When I had mine rechambered, I sent it to Frank Wells in Tuscon, Arizona. While we were talking about it he told me Weatherby was bringing it back. I was disappointed, because now everyone would want one. Good thing I was wrong.

He ordered the reamer and when I fired the rifle, it made the goofiest looking two shouldered cases you ever did see. I sent it back and Frank ordered another reamer. This one was perfect. Meanwhile, I had called Weatherby to see if I could get one piece of brass. At that time they said "no" since they hadn't receiver any themselves. I told them what I was doing and asked them if they would give me the chamber specs, they refused to do that too, since they wanted to keep it under wraps until it was official.

It was only a few weeks after this that a fellow posted on here that he had some genuine 1950's vintage, .375 Weatherby cartridges and brass for sale. He lived in Anchorage. I bought two full, complete boxes of cartridges (they have a tiger on the cover), and about 60 fired case; they match my fired cases perfectly. So, I think the difference between what I have seen in the books are incorrect, or I am measuring them incorrectly. I do note I can measure them according to the A-Square manual and they are the same dimensions, but not with a regular shoulder as A-Sq. depicts.

Anything mechanical has tolerances. That includes rifle chambers. And, any reamer may not be perfect. A correctly dimensioned .375 Weatherby reamer should clean up a .375 H&H chamber that is not oversized in ANY dimension.



Of course, as the Walgreen TV ads say, we do not live anywhere near "Perfect". So, when improving any pre-existing chamber, a person is always running the risk that it may not clean up perfectly. The reamer may be a little on the small side, the original chamber a little on the large side, or both. Some 'smiths at that point may run the reamer in a little deeper, if that will clean up the new chamber the rest of the way. Others may just call it luck of the draw.



As to performance, I'm not surprised if the general rule of expected performance increase does not apply in this instance. I suspect that is true in all of the best "improved" cases. Such improvements benefit not only from an increase in the amount of powder that can be used (more potential energy), but move the case capacity from just on the cusp of a proper burn of some particular powder, to a more ideal capacity/bore-ratio for that powder and bullet mass/sectional density.



Personally, I always liked the .375 Weatherby for 300 grain bullets, and still do.



AC