Fellow members.

I was wondering if its possible to expand a 300 RUM case neck to .375 caliber without to much issues. If yes, whats involved, and how many steps are required? I have a new set of RCBS 375 Ultra Mag dies.

I have the chance to get a couple boxes of once fired Federal 300 RUM brass (for free) from a friend. I was thinking of using them for range work when I get my 375 Ultra back. Please share your knowledge.

Thanks in advance.

Maurice

It's easy. I do it all the time with a tapered expander plug that I made from a 7/16" x 3" bolt. It fits in a RCBS .375 RUM espander die body.

I first cut the hex head off the bolt, then chucked the smooth end of the shaft in a 1/2" drill that I clamped onto my workbench. (My poor man's lathe)

I then cut down the bolt shaft with a file and finished smoothing it with emery cloth. I also cut a slot on the threaded end for adjusting with a screwdriver.

Then I just lube (Imperial Size Die Wax) the .30 RUM case mouth and expand it in one stroke. I've expanded at least 60 or 70 cases this way, and have not had a failure.

300 to 375 is no issue. I've taken 280s to 416 but usually stopped at 375. Either a tapered expander or a number of steps and then anneal

Buffybr, that is very ingenious!!! Wow, thanks for sharing your experience. Ok, now I know it can be done without a hiccup. I wonder if RCBS sells a tapered expander plug... How many reloads are you getting out of your brass? Any split necks yet?

Thanks again.

Enigma, I haven't seen anything like my expander plug in any of RCBS's advertizements. It would be very easy for them to make. It took my less than 30 minutes to make mine.

I haven't shot my .375 RUM since my last trip to South Africa in 2007. It's not my plinking rifle. I have almost 200 cases for it, including the ones I expanded from .30 RUM cases.

I have several boxes loaded with cast bullets that are good for plinking and practice shooting. My plan is to replace those cases with the .30 expanded ones.

I haven't had any split necks yet, but I don't think I've loaded any case more than 5 times. I do anneal the cases after about 3 firings, and I did anneal all the expanded cases after I expanded them.

Well thank you very much buffybr and everyone else who replied to this thread. I will call RCBS to see what they have to offer, and perhaps try to replicate your tool.

Thanks again everyone.

Maurice

Well folks, after reading Buffyb's post, and looking at his improvised tapered neck expander, I started thinking. What do I have laying around that could be used to do just that... I remembered that my 375 H&H Lee neck sizing die had a nice .375 caliber plug. I took the die apart, went to my gunsmith and asked him to turn the plug down from .373 to .300 on about 2 inches so that I had a very slow taper. I took a few pictures for you folks to see what I mean.



To make this modification work, you will have to replace the Lee crimp bushing with something else, either by another bushing that you machine, but that is costly, or, find a bushing... I realized that 1/2 inch straight copper couplings have an outside diameter that matches the crimps bushing diameter, roughly .700 inches. I went to my local hardware store, got a couple couplings, and bingo, they fit perfectly in the die. Cost for the two couplings, $2.50. Cost for turning the plug down on a lathe, $10.00. Total cost $12.50.



I tried a few different cases just for fun. A little Redding (Imperial) sizing wax on the inside of the neck, and I expanded two 7mm Rem Mag cases straight from .284 to .375 without any problems. I did the same thing with a 30/06 case and no issues either.




As you can see, I measured shoulder bump before and after, and noticed very little, between .003 and .004 inches.


Maurice

Hope you enjoy.

Thanks for sharing!

I won't go into the various modifications I've made to Lee dies to accomplish one or another thing; I'll just say that Lee dies are inexpensive, you can buy the component parts directly from the factory for a reasonable price, and since Lee's steel is usually a bit softer than most die steel, they modify more easily. They make a great platform for various uses; and if you know how to use them, Lee dies, thought inexpensive, work quite well.