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I've been lurking here for awhile and decided to register, in part to post information above on fire forming .30-30 cases for a .375 Win given the cost and relative scarcity of .375 brass and give back to the hive for some of the information I've found and used already.

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I found a few sources on the internet suggesting 6-8 grains of a pistol powder, corn meal, cream of wheat, grits, etc, but nothing very exact nor definitive, so developing a suitable load was still something of a crap shoot.

What I eventually settled on to blow out new Winchester .30-30 brass was 6 grains of Unique, with cream of wheat on top to fill the case to about 3/16" below the top of the case. With my particular lot of cream of wheat, this was 22.5 grains in the powder measure - your lot may vary as cream of wheat does not come in a canister grade and I suspect the acceptance criteria on cream of wheat is pretty broad.

To create a wad to hold it all in the case, I stacked 6 sheets of toilet paper and cut it in thirds, then cut each stack of strips in thirds to get nine squares per sheet. I rolled one of the squares into a ball and placed it over the cream of wheat in each case and pressed it down firmly with a suitable sized drift punch to pack the cream of wheat and secure the load in the case. The wad top of the cream of wheat ends up being just above the start of the neck.

The resulting load was then fired while holding the rifle vertically. This helps the brass flow evenly and keeps the necks much more concentric and even in length. There were no indication of excess pressure, but pressure was adequate to full form the case. The TP wad and cream of wheat travel upward about 10-15 ft and fall back to earth. Either shoot them on a really windy day, or wear a hat to keep it out of your hair.

I have had about a 3% failure rate with about 1 case out of 100 developing a noticeable split on fire forming, and about 2 out of 100 developing small splits on the first actual firing. I can live with that.

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The resulting .30-30>.375 cases came out averaging 1.998" in overall length with a range of 1.995" to 2.000". They are on average about .01 shorter than my Winchester .375 Win cases, but also more consistent in length than the Win .375 cases which had a range of 1.998" to 2.015". This perhaps does not say much for Winchester quality control and speaks to the need to trim all your cases to the same overall length to facilitate accuracy, consistent crimping, etc.

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The total internal volume of the new .30-30>.375 cases cases after their first actual firing in my .375 chamber is on average 5.1% larger than the .375 Winchester cases after their first firing. Consequently, despite some rumors to the effect that .375 brass starts with the same basic case as the .30-30 in current production brass, .375 Win brass does indeed have substantially thicker case walls than .30-30 Win brass, so I'm limiting pressure to the same 40,000-42,000 psi class with the fire formed cases and reserving the actual .375 brass for use in full power loads.

There was some overlap between the volume of the largest .375 cases in the sample and the smallest .30-30>.375 cases in the sample, but the thing to consider is that the largest volume/thinnest cased .30-30>.375 cases were larger/thinner than any of the .375 cases, so you need to avoid 50,000 psi pressures in the .30-30>.375 cases to stay out of trouble with the cases on the thin end of the range.
 

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I took an old RCBS 30 Carbine decapping die and turned the stem down on the lathe to .375", a dip of the neck in the ISDW and in one stroke on the press, bingo! 38-55 brass.
 

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I just resized the neck in a .35 Rem. die then full length sized in a .375 Win die. The cases I used were Remington and Federal.
The Federal cases were OK for cast bullets sized .377 but did not have enough tension at the case mouth to hold J bullets. The Rem cases were a waste of time. They didn't work with either jacked or PB bullets. And yes I DID NOT use the expander die just a LEE die that belled the case mouth.

The .30-30 cases probably would work just fine with the .38-55 as a larger diameter bullet is used.

The .30-30 cases were also too short so I couldn't crimp without readjusting the dies.

Hip
 

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While there's no doubt that the .375 can be loaded to higher pressures than the 30-30 is normally loaded to, neither is the .375 loaded to .270 pressures. Or anywhere near it (do not be fooled by the ambiguous and misleading "50,000 CUP" listing). Thicker brass has more implications for case life than safety if reasonable caution is used. Many .375 loads really do not exceed the 42,000 ish PSI of the 30-30.

Greatly higher pressures for the .375 are not the reality of most hand loaded data to be found for the cartridge.
 

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Model 52, Welcome to the forum! Good to see new posters who know what they're about. That's quite a first post! One suggestion.........use the bacon or apple-cinnamon flavors, and you can make the neighborhood smell wonderful as you fire-form your brass. I used 6 grains of Bullseye and bacon-flavored grits, and as soon as I was done I had to go find something to eat!
 

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I just resized the neck in a .35 Rem. die then full length sized in a .375 Win die. The cases I used were Remington and Federal.
The Federal cases were OK for cast bullets sized .377 but did not have enough tension at the case mouth to hold J bullets. The Rem cases were a waste of time. They didn't work with either jacked or PB bullets. And yes I DID NOT use the expander die just a LEE die that belled the case mouth.

The .30-30 cases probably would work just fine with the .38-55 as a larger diameter bullet is used.

The .30-30 cases were also too short so I couldn't crimp without readjusting the dies.

Hip
I suspect the specific chamber it's fired in makes a difference here, but .376 diameter bullets are only a slide fit in my fired .375 brass as well as the .30-30 brass. .380 dia bullets can be pressed in the .30-30 brass but are about perfect for the fired .375 brass. As it is, I back the sizing die off and size the cases just enough to give adequate neck tension.

I have also migrated to .380 diameter cast lead bullets given the rather generous chamber and leade diameters in my Model 94 as it seems to help accuracy and allow bit more velocity with non gas checked bullets than a smaller diameter bullet. So basically I run it like a .38-55 "short" most of the time. Big bullets and lower velocity seem to suit the fast rifling twist better anyway.

One of the few advantages of having a .375 rather than a .38-55 is I can trim the cases (.375 and .30-30>.375) all to the same length and the bell and crimp dies stay happy.
 

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Model 52, Welcome to the forum! Good to see new posters who know what they're about. That's quite a first post! One suggestion.........use the bacon or apple-cinnamon flavors, and you can make the neighborhood smell wonderful as you fire-form your brass. I used 6 grains of Bullseye and bacon-flavored grits, and as soon as I was done I had to go find something to eat!
Great idea!
 

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While there's no doubt that the .375 can be loaded to higher pressures than the 30-30 is normally loaded to, neither is the .375 loaded to .270 pressures. Or anywhere near it (do not be fooled by the ambiguous and misleading "50,000 CUP" listing). Thicker brass has more implications for case life than safety if reasonable caution is used. Many .375 loads really do not exceed the 42,000 ish PSI of the 30-30.

Greatly higher pressures for the .375 are not the reality of most hand loaded data to be found for the cartridge.
That was pretty much my conclusion and the reason for going with .30-30 brass. I can't think of many loads I'd use for my .375 that would exceed the 42,000 psi mark. Those that do are not something I'd want to feed on a regular basis to a model 94 due to potential bolt set back issues.
 

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That there struck me as funny! First thought popped in my mind was a "30-30 grit gun". LOL - Grits dry like concrete and I had this mental image of making something like a grit shot-shell. That'd sure be something on small critters and birds. ;)
 

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I had this mental image of making something like a grit shot-shell. That'd sure be something on small critters and birds. ;)
They'd be pre Bacon flavored!:flute:
 

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Marlin 38-55, Winchester 375 bullets

I just resized the neck in a .35 Rem. die then full length sized in a .375 Win die. The cases I used were Remington and Federal.
The Federal cases were OK for cast bullets sized .377 but did not have enough tension at the case mouth to hold J bullets. The Rem cases were a waste of time. They didn't work with either jacked or PB bullets. And yes I DID NOT use the expander die just a LEE die that belled the case mouth.

The .30-30 cases probably would work just fine with the .38-55 as a larger diameter bullet is used.

The .30-30 cases were also too short so I couldn't crimp without readjusting the dies.

Hip
I would like to point out that while the shorter cases are a bit of an issue for Winchester 375 loaders, they can be a boon for reloading 38-55 rifles. The reason is that with a shorter case one can use cannelure bullets intended for the Winchester 375, crimp them, and still not exceedi the maximum loaded cartridge length for the 38-55.

This seats the bullets in the throat like they should be with little free bore.

My current 38-55 is a 1960's Marlin/Glenfield 336 with a pre-WWII 38-55 Marlin 36, 26" octagonal barrel (marked "smokeless powder"} and a full length tube under it. I have a Lyman receiver peep sight on it that was put on in the 60's.

A chamber/bore cast showed a neck diameter of .392 and the barrel is .376. This means that Winchester bullets shouldn't be accurate but they actually shoot quite well. Didn't get the full length of the chamber;)

By the way, the Winchester 375 is supposed to have a neck diameter of .400; however I have never measured one.

I have been using 38-55 Dominion cartridges that I bought in the early 1970' and they are still hanging in there. I use them with 38-55 cast bullets. The short blown out 30-30 cases get the Winchester 375 bullets. The Dominion cartridges were bought loaded with 255 grain jacketed bullets. They produced 1700 fps in my rifle.
 

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I bought a Marlin 375W last year. I didn't have much brass so I made up a few out of 30/30 brass. I annealed the necks first, loaded
up with Bullseye & corn muffin mix and fire formed. As already posted Remington 30/30 brass is no good for this. Cartridges worked
out fine, but only loaded to 38/55 specs, not full power jacketed loads. I ended up trading Marlin off for Ruger #3-375W & got a good
supply of 375W cases. I have been using the blown out 30/30s to experiment with stout loads with 375H&H bullets. Cases have been
holding up. With RCBS die I couldn't get neck tension for jacketed bullets, dug out old Pacific sizing die that did the job with no crimp.
 

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