336 rebarrel thoughts

[sukivel]

Eventually I’ll find a 375 win JM some day and have fun casting up some loads for it.

Me too!


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[TomAM]

Your boolits should be at least .378" diameter, since the barrel is 38-55.

[TomAM]

The 375 Winchester in a nutshell:

The cartridge was introduced at a time when the 38-55 was nothing but a distant memory. 38-55 ammo and brass were obsolete.

Winchester decided to make a more powerful, modernized cartridge using a shorter case and modern .375" diameter jacketed bullets. The pressure generated by the new cartridge would be moderated by using a 38-55 barrel, whose .378" groove diameter and oversized chamber would allow significant gas leakage. The concept was doomed from the start, because this is a recipe for very poor accuracy.

Fast forward to present day. 375 Win brass is now rare and expensive. 38-55 brass is plentiful. 38-55 bullet molds of proper diameter are common; easily available. Why would a boolit caster even want to try to shoot 375 Win in a perfectly good 38-55 rifle?

[Tripplebeards]

More and more I think I’d probably go with a 358 Winchester. You’ll never run out of cheap and range pick up 308 brass to re size.

[country gent]

Check and make sure all the attachments to the barrel ( fore arm mag tube barrel band) are lined up and not under any stress. It sounds like a stress issue with the barrel wanting to walk as it heats up.

Is there any pattern to when the fliers happen Ie always the 4 and 5 shots in the group? Shoot a slow group a round every 2-3 minutes giving the barrel time to cool out and relax. If the fliers go away here its probably a bind between fore arm, mag tube or a barrel band.

[rockrat]

Another cause of vertical dispersion is bench technique. If you don't hold the gun exactly the same every time, it can rear its ugly head. Friend had a BAR in 308. If he was a bit sloppy at the bench, 2-3" groups followed. If he really worked hard at consistency, groups slightly under an inch was common. I am sure the recoil on the 375 is a bit stout.

[Tripplebeards]

Every time I had a good sized vertical shot string over the years I would always find out my optic shifted backwards. Good thing I bought a wheeler torque wrench a few years back. Saves optics and ammo. I also get groups that will jump around with my 7600 if I don’t have it rested properly in my lead sled and with a good grip on the fore end. If it just jumps around with not holding the gun in place my ladder testing groups are all over the place.

[TedH]

I have spent the last 20+ years shooting and loading for several 375 Winchester rifles. Winchester, Marlin, Savage, Ruger, and a Marlin 30-30 that I had rebored. As others have said, the rebored Marlin is perfectly safe to shoot with 375 Win ammo. My Marlin Model 375 had a similar problem as you are experiencing when I first bought it. I played with the stock, mag tube, etc. as others here have suggested. I eventually fixed it when I found the firing pin to be very gummed up, sticky, and hard to move. Apparently resulting in inconsistent ignition.
Bench technique is important with these leverguns too. Consistent grip pressure, and how you pull the butt into your shoulder will make or break a group.
There is one load that has always, and I mean always shot very well in all my different 375 rifles. The 220 gr. Hornady bullet with 36.0 gr of RL7 and a CCI standard LR primer. If a rifle is capable of good accuracy it will shoot that load very good. Unfortunately Hornady discontinued that bullet several years ago and the remaining few are hard to come by.
I mostly shoot cast out of mine now from the Ranch Dog 235 gr mold. I use the same 36.0 gr charge of RL7 with that bullet too.
Good luck, and let us know when you get it straightened out.

[SoonerEd]

If it has a barrel band as opposed to a fore end cap, make sure the barrel band is not touching the barrel. If it is Get some emery cloth and a dowl rod to relieve the barrel band. You should see light between the band and all points on the barrel. The other issues to check is the mag tube touching the barrel and then the forearm needing to be to be relieved from the barrel. But, check the barrel band as its the most common culprit and can greatly affect accuracy as the barrel heats up. I've got a 30-30 336 that shot 8" groups as the barrel band was binding particularly bad. It now shots 1.25 MOA constantly and I get occasional 3/4" groups but I did additional work including squaring and floating the mag tube, free floating the forearm and minor polishing of the trigger.

[FergusonTO35]

Quick tip from my experiences with sloppy Winchester 94's: Gorilla tape makes an excellent material for quickly bedding small areas, filling gaps, and/or improving parts fit. A few little strips snugged up the super sloppy mag tube and forend fit of my beater 1985 model and it's still tight as can be after a few years. I see no indication that hot or cold has much effect on it.

[murf205]

How much of a problem is it to swap the magazine tube for a short one? You would have to have a different fore end and cap too, right? It has been my experience that the short tube guns with the lack of a barrel band are a lot more accurate.

[MostlyLeverGuns]

Most Marlins with a barrel length magazine tube AND a forearm band and muzzle band have only notches for the screws that go through the bands to hold the magazine in place. To shorten the magazine, at least one dovetail, if not two will be needed to to hold the magazine tube. Two dovetails is how most of the 1895's with 4-5 shot magazines hold the magazine tube, same with the 444S model and later.
It is not uncommon to have the forearm band screw bend from recoil after much shooting making it very difficult to get out. A heavier cross screw in the forearm band, deepening the notch in barrel can work if the forearm is glass bedded or epoxied to the magazine tube, but this fix is pretty permanent. I did this to a Marlin 336 .35 Rem, changing it to a 3 shot magazine and it shoots very well. I did this long before the Remington debacle, when used Marlin's were inexpensive and very common.

[Shawlerbrook]

Had one shortened and the front barrel band removed in lieu of a dovetailed hanger.