Customer questions about the 375 Winchester

Hi my name is fordwannabe over on paco kelly. I started a thread about the 375 Winchester and I saw that you have booklets for it. Seeing as how I have no experience with this round....what can you teach me about cast in the 375. I cast and load for a bunch of dash calibers 30-30 32-20 44-40 &38-55 among others. I have the Lee mold for the 38-55 is this a possible canidate? What bullet are you selling a lot of for this caliber? Thanks

G’Day Sir

Ah the 375 Winchester a cartridge of which I have a great fondness for. Why do we have it, what was its purpose, what were they thinking are all questions I have asked myself. At first glance it would seem that Winchester as with other chamberings had just brought back the 38/55 with a new name but on delving into the mechanics of the cartridge we see that its really a whole new creature. There are similarities but they are more different than similar.
First off they are different calibers the 375 Win being a 37 cal and the 38/55 being a 38 cal. Secondly and this is a game changer for application they use a different twist. Where the 38/55 was a deer and target cartridge that excelled for those purposes it was built at least in the factory offerings with a 1/18” twist targeting mainly bullet weigth in the 250gn area. Other twists were available but these were mostly one off propositions built by the masters of the day built for target competition and these rifles excelled for this purpose. Consider the Rowland – Pope group. Without referring to reference material I will go on memory and try to get close with the numbers. A Dr Rowland shooting a Pope barreled 38/55 shot a 40 rod (220 yard) group using black powder and iron sights placing 10 shots into 3/4”. I believe this held the world record for nearly 70 years. Check for the actual numbers but I believe these are close.
Another modern change between the two cartridges is pressure. Where the 38 cal version was always limited to black powder level pressures of about 25,000 psi the new 37 cal version would push that envelope to the maximum of what modern lever action rifles would tolerate, something in the 40,000 area.
Now lets get to the “ what were they thinking “ part. Way back about 1912 when Holland and Holland came out with the 375 flanged magnum they set the twist rate for their cartridge at 1/12”. They decided on this twist rate with a purpose in mind. That purpose was to apply enough spin to a 300 gn full patch bullet to maintain a straight path in its terminal penetration of very large animals. As the history of the H&H cartridge shows us they were quite successful in their endeavor.
Now this is the part I have never been able to figure out that when the Winchester engineers decided on the same 1/12” twist for their cartridge were they knowingly designing the greater potential into the cartridge or were they just without regard going with what by that time had been established by H&H as standard for the 375 caliber. So many times have I asked myself why did Winchester give their cartridge this fast twist but never offer it with other than the same bullet weights of the 38/55. To my knowledge the main offering was a 220gn jacketed bullet load.
This question I did ponder and decided for my use I would not limit myself to bullet weights and designs intended for deer hunting.
At the time of my messing's with the 375 Win I was living in the Alaska interior so all my intended targets would be much larger and heavier than deer being moose, caribou, and interior grizzly bear.
Knowing that the Barns bullet company for several decades had offered its original copper tubing bullets in a 375 cal 350gn round nose design I decided to target that weight area to exploit the real big game potential of the Winchester cartridge. In this endeavor I was eminently successful. My pet load for the cartridge uses a 350gn WFN design cast bullet with a muzzle velocity of 1550 fps. This velocity may sound rather anemic but my oh my how it does a smashing job of penetrating flesh and bone. This energy conserving weight combined with the wide meplate bullet design work together to create very wide and deep permanent wound channels that drop oil pressure in big critter systems FAST!
Now if pressed to give an opinion on a first favorite choice for the Winchester cartridge this bullet and load is it.
However not being so pressed but by your questioning asking of the most popular bullets sought by our customers I would have to say that customers that ask for a specific bullet most often ask for the Lyman #375296 or the RCBS 37/250. Both these are gas check designs with the Lyman version finishing at about 280gn in a moderately malleable alloy while the RCBS is closer to the 250gn as advertised.
We have other designs available but these two are the most popular with customers.
Let us know if we can be of further assistance. We will be happy to serve your bullet needs.
The Bullshop