Issues with Marlin 375

[johnly]

The issue is finding a mold that casts a bullet fat enough for the ~.380" bore. My two molds cast bullets that drop about .378" and skim sizing them to keep as much diameter as possible still result in keyholing bullets if the velocity exceeds ~1000 fps. If a load them way down, the 100 yard accuracy is in the 2" range.

Suggestions?

John

[beagle]

Beagle your existing mould and try it. You should be able to get .003" easily. I did that recently for a friend's .38/55 and it turned out all right./beagle

[runfiverun]

even with the ones that i can get to 380 i don't have enough rear sight to get to100
yds. even at 1500 fps.
oh yeah win 38-55 brass will fit easily enough in mine also.

[ktw]

I have a Lyman 375449 that casts at .377. I get great results with it in a .382 bore by paper patching it up to .382.

-ktw

[6pt-sika]

I size all my bullets for the 375 Marlin in a .379" die ! Have had very decent lick with a couple Lyman/Ideal moulds and a RCBS mould as well ! One of the Lyman/Ideal moulds is plain base and the other two are gas check !

Very soon Ranch Dog should have his .379"-235 GC mould available !

I've done a bit of work with bullet and quite a bit of work with his original 375 offering the .379"-210 GC matter of fact I killed a deer this past season with the 379-210 bullet !

Check out ;

www.ranchdogmolds.com

[Ranch Dog]

John,

I've been working with the 375 Win for a number of years, have owned three of them but now down to two rifles, one a hunting rifle and the other NIB. I've actually found them to be very tight bored, with deep cut rifling and huge throat/leades. Here is an image of my hunting rifle's chamber and it is identical to all three of my rifles.

http://www.ranchdogmolds.com/TLC379235RF/Drawings/TLC379235RF_375_WWS_Cutaway.gif

The neck at the step diameter is what shooters often mistake for the diameter. You still have a lot of chamber to fill to reach the bore and a .380" bullet isn't going to get there. The flatter the nose, the worse the fit.

This cartridge and the 38-55 Win are often compared but this area described above is where the difference is and it is very significant. The 38-55 Win doesn't have this grand of throat/leade to fill for proper bullet fit. I can only speculate about why this cartridge was designed with such an expanse between case rim and bore but have come to think it helps dissipate the tremendous pressure generated by this cartridge in an unmodified 336 frame. Factory ammo generates 55.0K PSI when shot from my strain gage equipped rifle.

As a reference, I'm getting great results with a full loads of H322 and H4198. One of the sort comings of the 375 Win is that there is a very small range of powders that produce the necessary pressures from the limited case capacity to achieve factory type velocities. With the bullet I've settled on, both of these powders are producing 1.09 to 1.91 groups at velocities of 1948 to 2082 FPS depending on the ambient conditions for the given day.

This is just my findings, I've been working on this project about 4 years now and I'm finally satisfied that I have a 375 shooter that can compete with the velocities generated by factory ammo.

[johnly]

I slugged the bore from the muzzle to the chamber and it measures 0.380". I can try it from chamber to muzzle, but I doubt that will change things.

John

[Ranch Dog]

I can try it from chamber to muzzle, but I doubt that will change things.

Yeah John, I suspect that won't change a thing;)

Just out of curiosity, what material are you using to slug your barrel with? I found a short cast of cerrosafe or an "egg" sinker, the sinkers with the hole through the longitudinal axis, to deliver the most accurate results. Everything else starts to expand the second it leaves the barrel. Cerrosafe must have math applied vs. time but the hole through the egg sinker seems to provide enough relief to the alloy to allow it to remain dormant after it passes through the bore.

This is a target from my "Hunter" Marlin 375 (read "beater") with the load being 36.0-grains of H322. It has consistently provided me with these 1/2" 5-shot groups at 50-yards and 1" groups at 100-yards with a muzzle velocity of 1950 FPS. I'm pretty happy with that velocity as the Winchester 200-grain PP factory ammo only generates 1928 FPS.

http://www.ranchdogmolds.com/TLC379235RF/Images/360.gif

I really like this cartridge and the Marlin's chambered in it and it is a real shame it didn't take root. It would actually make a fine rifle/cartridge combination for me here on the ranch and now that I've finally got the bullet figured out to my liking, I suspect it will start to get used as much as my 444T.

[johnly]

I drove a cast bullet the length of the barrel using a brass rod. The lead was a hard alloy.

John

[Ranch Dog]

You might want to try the egg sinker John. A bullet, particularly a hard cast bullet, is going to react to the compression (that's why we like shooting them). Its also why you want to size bullets cast of tough alloy or with any kind of treatment rather soon after casting.

I also use a wooden dowel to drive the sinker through the barrel. With the dowel, there is no reaction to the beating other than the resistance provided by the bore as the dowel is softer than the lead. I use a dowel that just about fits the bore.

I have seen some Marlin 375s that are extremely eroded at the throat and I suspect that is from a life of a lot of factory ammo and/or reloads with jacket bullets. The short length of the available jacketed bullets requires quite a jump across the long throat and there is plenty of pressure behind them (up to 52.0K CUP or 60.0K PSI).