I am thinking about making a 375 wildcat similiar to the 375 Dakota by taking the RUM case and shortening it to the same dimensions as the Dakota. I've read that the Dakota and the RUM cases are derived from the 404 Jefferey except that the RUM case has a smaller diameter rim. Is this correct? If so, can I use the 375 Dakota dies and a RUM shell holder to load my rounds? The reason for this project is that I have a Ruger laminated stainless in 7mm available. I figure I would not have to open up the bolt face to take the 375 Dakota-RUM, the smith could just use a 375 Dakota reamer, and cases are cheaper. Is there a wildcat like this out there already?

The Rum is supposed to be a rebated rim 404, but I'm not sure that is exactly true. The references I've seen list the 404 as having a .540" dia case head, but the Rum brass I have has measuered .550" dia for a virgin case, and .555" dia for a fired case. Speculation has been that the RUM is really a .348 Win case lengthened, and with a rebated .532" dia rim.

I haven't seen any prints or Dakota brass to know what dia they run. Ken Howell came up with this wildcat in the early 80's, and it was called the 375 Howell, it also had a 416 and 458 brother. All rounds were based on the 404 case, the 375 and 416 were 2.500" long, the 458 2.550" long to provide a longer neck. I have an article on the rounds but will have to dig it up.

Here are the dimensions on .375 Dakota brass .375 Dakota

Something to consider:
For the price a Dakota die set, you could have your own made by CH4D or like, and not worry about brass fit. The RUM is bigger, and will be swaged everytime you use the Dakota dies. But you could use the Dakota die for neck-size, but why?
I say choose one or the other. I'm a fan of the 404 case, and had my cat made from it, not a rebated version, not a slightly altered for propriety version. It'll be around for ever, and has a pedigree. But if you make a cat off the RUM (good idea) jsut have the dies made same.
T

Thanks for all the help guys. I did not know that the RUM case was bigger in diameter. Thought they both had the same diameter. I am going to go with the RUM based wildcat due to the fact that the brass is cheaper and more available. Thanks again.

If you're really looking for cheap and available, why not consider the 416 Taylor? The other option would be converting your Ruger to take the full length magnum magazene, and then just chamber it as a 375 H&H.

The Rum is supposed to be a 404 case, but it really isn't. The reamer and reloading dies are going to be suprisingly exspensive, so you really might want to consider something that is already out there.

How about necking up the 338 RUM case to 375?

Just an idea.

Snapper

Paul, actually that is another viable option. Lengthening the M77 and chambering it for the 375 Weatherby.
Snapper, thanks for the suggestion also.

I have made some of these cases by pushing back the shoulder of the 338 RUM, expanding to .375 and cutting off the excess to 2.500 inches. The 338 brass is easier to work as it is already a short 2.296 inches to the shoulder, so you have less pushing back to do.

An easier and more interesting wildcat is the 375 WSM, which will easily duplicate the 375 H&H from a 2.8 inch round in a short action. You will get about 100 fps less with the WSM case than the RUM shortened to 2.50 inches but what you gain is a case that is much easier to form and far superior for reduced loads. Sure a 300 grainer at 2600 fps is a fine stopper... and the 375 WSM will do this, but it is nice to pop out a 225 gr Hornady at the same velocity for deer, too.

With all this said, this performance is no different than the 375 taylor, which is the 338 Win necked up to .375. That's easier yet, but you will be back at a 2.5 inch case.