View Full Version : Need 375 Supermag brass

12-02-2015, 01:19 PM
I just bought a Dan Wesson 375 supermag and 357 SM, have 20 rounds of IHMSA 375 brass but that will be stashed away and never used.
Im looking at making brass from 30-30 and 38-55 brass but would like to know if either will hold up to full pressure loads?
will use 375 Winchester brass when I can find some.

12-02-2015, 01:22 PM
Here's what I found out when I tried making 375 from 30-30.

Well after spending 2 days working on the 375Win and the 375Supermag I found more than a few ways NOT to make them from 30-30 brass. The length of the 375Win case is 2.020-.020 and when forming those from a 30-30 case that's already at 2.020 the case shrinks to 1.980 which of course is to short for my tastes. Everything else is fine after forming but those aren't something I could stand up and be proud of. So needless to say I wont be doing those.

The 375Supermag was interesting to fiddle with. After doing all the work to the 30-30 case in order to make them into 375Supermag I found out when everything was all said and done there's problem(s). 375Supermag brass is thicker for a reason, after converting a few the cases of the 30-30 being as thin as it is will not properly hold the boolit and pretty much falls right in the case. The 30-30 case weighs 10gr less after forming than a 375Supermag cases do. That 10gr difference equals about a .004 thicker case (.002 per side) for the 375Supermag which is what is needed to hold the boolit. So that's another conversion I wont be doing

12-02-2015, 02:52 PM
I have never formed brass for the 375 Supermag but have formed plenty for my 375 Win.

In terms of strength 375 Win cases are thicker in the head area than 30/30 and 38/55 are thinner than 30/30 cases in the head area. That doesn't mean you can't use them, all it means is you should segregate them and use them accordingly.

I have measured a number of 30/30 cases from a wide number of sources and the weight variation is staggering and almost rivals the 22 Hornet for case variation. The point is stick to one brand if you are going to use them for full power loads.

Of the 30/30 cases I have used PMC cases (no longer made) proved to be the strongest and most durable, followed by Winchester.

If using new brass there is no need to anneal the cases, but with old, work or age hardened brass you will have a higher success rate if you anneal the neck and shoulder area first.

Opening up 30/30 brass to 375 results in a shorter length and brass that is thinner in the neck area compared to factory 375 Win brass. I size bullets to 378 and use a Lee FCD to secure the bullets to achieve the correct OAL and have never experienced an issue. If as Grumpa mentions the case walls are too thin when the cases are shortened to 1.6", you might consider using a larger diameter cast pill, providing they still fit the cylinder. Before trying to convert a heap of cases I would suggest you weigh and section a few different brands of 30/30 cases to see which brand is likely to work best for you.

12-02-2015, 05:10 PM
Off the top of my head and without looking up the measurements, I doubt if 303 British brass will work, but you might look into it.


12-03-2015, 01:37 PM
Thanks guys for all your help, found 200 new IHMSA 375 cases for a lot cheaper than buying 200 375 win cases and have a lead on a couple hundred more.
I thank you members that have spent the time to try this and share your experiences.
saves a lot of wasted timed.
Thanks again!

12-25-2015, 09:08 PM
Glad you found brass. I just made some 375 SM from 30-30. I cut the brass at about 1.610 with a tubing cutter, ran it through the expander die, then the sizer and then the expander a second time. I then trimmed the brass to 1.600". I kept loading a number of the same cases during load development to get an idea of case wear. After 6 loadings, I could not detect and length increase and had no failures. This is just a guide as I was using some more conservative loads. Hope this helps.