375-300 rum?

I have a young friend that shoots a 300 RUM and can only find ammo at $90+ a box...
So I tell him to bring all his fired brass over and I'd teach him how to reload. He has not been saving his brass...
I have a new bag of 100 or 200 375 RUM brass and was thinking about just necking the 375 down to 300.
I don't have the dies yet, or I would have just tried it already.
Has anyone done this with good results?
I may have a 325 WSM die set that I could use an an intermediate step.
I still have to order a set of dies, just not sure if I need to find some 300RUM brass to go with it.
TIA
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Just checked Midway, the only brass available is $4 ea, so I just ordered the dies.

Check with the member here that goes by 725. That's where I got some .300Rum brass a while back.

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As he doesn't reload, I would shy away from wrong / incorrect headstamps. But thats just me.

The shoulder location is supposed to be the same for the 7mm, 300, and 375 RUM. Lord knows why they made the 338 Rum case shorter, though, but it woukd not be a good candidate for conversion.

The conversion will work fine though, but likely require intermediate neck sizing.

Do you have a .35? lee bullet sizing die? That might work for the step from 375 to about 338 caliber.

.375 + 0.015x2 neck walls = abou 0.400-0.405 OD

You want to end up with about 0.335 OD after the FL sizing step.

I have used push through bullet sizing dies with decent success in necking down operations.

The leverage on the press isn't really where you want it, but it works. You wont be forming hundreds of them anyway.

I have both a 300 and 375 RUM. That 375 RUM brass is impossible to find. I paid an arm and a leg for some years back. I had a bunch of 300 RUM brass last year that was worn out. The necks were so thin that that would not hold a bullet. I ended up buying new brass and it solved my problem. The two brass cases should be identical. If you don’t downsize them for him I’d trade you for? It’s just the head stamp isn’t going to match but guessing you could get them to work.

The dies showed up today, so I tried a 375 RUM case into a 300RUM die slowly a little bit at a time and the shoulder buckled. I dug around and found a 338RUM die, used it as an intermediate step and it looks like that will work.
I'll have to wait for the young man to bring his rifle over and fireform it to see for sure.
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