ROT 375 for Win Rebore?

[Suo Gan]

I am going to have a couple of 30-30's rebored to 375 Win. I was wondering if anyone had any input into the rate of twist I should go with. Also what would be your preferred number of grooves for this project?

Thanks for the input!

[Bullshop]

The rate of twist should be determined by what boolits you intend to shoot out of it.
The 375 win came out with a 1/12" twist which was way too fast for the bullet weights it was offered in. The heaviest 375 boolit design I have is about 370gn depending on alloy and it shoots fine in a Marlin 375 Win.
I think standard for the 38/55 which is a very similar cartridge was 1/18" and was good for the 250gn bullets that were as far as I understand the norm for it.
I have a 38/55 with a 1/14" twist and it shoots the 330gn Lyman Postell style boolit just fine.
Decide what you want to shoot in it and go from there.
I should also mention that I now have about 6 rebores from Jes Ocumpaugh all having the three groove deep cut rifling. All are excellent boolit shooters.

[John Traveler]

If those rebored barrels are intended for conventional Winchester M1894 and Marlin M336 lever action rifles, it might not be a good idea. Winchester and Marlin beefed up the receivers for their .375 Winchester caliber rifles to handle the increased breech thrust and chamber pressures.

[Suo Gan]

The rate of twist should be determined by what boolits you intend to shoot out of it.


I got called away as I was posting this and got distracted.
I will be shooting 250 grain boolits maybe up to 300, don't plan on ever running a jack through them. What boolit weight to you feel is a good weight and rate of twist combo for hunting purposes BS?

Thanks for the info on the 3 groove rifling. That is the way I was leaning anyway.

I spoke with Jesse today on the phone, and he said he did not see any problem whatsoever chambering a 336 or a 36 for the 375 Win.

The 336 action was chambered for 375 by the factory some years back, as well as 356 Win, 38-55, 45-70, the new 338 MX and 308 MX, and of course 444 Marlin. They are a strong action, I have no real fear with them using sane loads.

[Bullshop]

You are right about the 336 action but not so with the 36. The 36 was a transition model using stocks and barrels of the new style as in the 336 but the actions were left over model 93s they were trying to use up, at least that is my understanding at this point. The Model 36 has the square bolt much like the current model 94s with the right side of the receiver being open. The 336 has a closed receiver with the round bolt.
I do not believe the model 36 to be as strong an action as a model 336.
If I had a model 36 that needed re bored I would have it chambered for the 38/55. That way you could load it anyway you want to but if someone else ever gets the gun it will be chambered to a cartridge appropriate to the action strength.

[Suo Gan]

You are right about the 336 action but not so with the 36. The 36 was a transition model using stocks and barrels of the new style as in the 336 but the actions were left over model 93s they were trying to use up, at least that is my understanding at this point. The Model 36 has the square bolt much like the current model 94s with the right side of the receiver being open. The 336 has a closed receiver with the round bolt.
I do not believe the model 36 to be as strong an action as a model 336.
If I had a model 36 that needed re bored I would have it chambered for the 38/55. That way you could load it anyway you want to but if someone else ever gets the gun it will be chambered to a cartridge appropriate to the action strength.

I asked him that specifically (38-55 or 375 Win in a 36), and he is not here to defend himself so will leave it at that he saw no problem with the action strength of the 36 for either of the cartridges.

From what I understand the 1936 and the later 36 took too much hand fitting, and too much machining, so viola the 336 was born. They are with all intents and purposes identical to a 336, but then there is that little issue with the entire right side of the bolt out in the air...it does make you wonder and think it probably is not as strong as a 336. I would be interested in the Rockwell hardness of the action, and even the barrel of a 36. Does Jesse do this?

What boolit weight and rifling twist do you recommend for a 375 Win, Bull?

School me on the 38-55, whats the brass situation using the two rounds?

[Bullshop]

In my view the reason the 36 is not as strong as the 336 is that the bolt or breach block which ever you will call it is only contained on one side in the 36 and as opposed to both sides in the 336 just as you said. Both actions are rear locking so the bolts are susceptible to flexing under pressure. With the enclosed bolt 336 the bolt can flex to a point then is in contact with the receiver and so gets additional support. The open sided 36 gets no additional support on that side and so can allow the bolt to flex without restriction and cause a case head sepperation or rupture where the 336 would have a better chance of digesting the same load without incident.
You are asking the wrong guy to recommend a boolit weight. I have lots of molds in the caliber and would like to use all of them. If you have a couple molds already use that to determine your twist. If you dont have molds yet decide what you would like and go with that. The old standard twist with a 1/18" gave the 38/55 quite a good reputation as a deer rifle. If however you can envision yourself say shooting the long range lever class at the Quiggley the 1/12" shooting something like a 330 to 350gn Postell style boolit will sure slice through the prevailing conditions.
You know what I mean is it all depends.

[doubs43]

I have two Winchester rifles in 38-55; a Hi-Wall and a '94 Oliver Winchester Commemorative. Both have 1:18 twist rates and both are quite accurate using Lyman 248 grain boolits. The Hi-Wall is also very good using the RCBS 312 BPS boolit so I'd say 1:18 would serve you well. If, however, you plan on competing in events using heavier boolits such as Bullshop mentions, 1:12 may be the better choice.

[Suo Gan]

Thanks for the input fellas.