It is easy to make .307 or .356 Winchester brass from the .444 Marlin case.
The only step after forming to keep firmly in mind is to keep the shell holders separate. If you forget and use a .30-30 shell holder on the formed .444 Marlin case you will pull through the rim and stick a case in the size die.
.356 Winchester cases formed from the .444 Marlin case will accept all maximum loads you use in the Winchester .356 cases except they will shoot to a different point of impact. They are not far off, but they are different.
Case life is good but I anneal the case mouth after forming.
The mid 1960’s American Reloaders Association Bulletin (ARAB) had some short articles and discussion by P.O. Ackley, Robert Hutton, Dean Grennell and a few others on making the wildcat .30- and .35/.444 wildcats.
The first mainstream magazine article I am aware of was by Wm. Schumaker in the December 1966 issue of Guns Magazine. This article was about the .30/.444 wildcat in the Model 94.
Myron Rockett had his .308/.444 article in the 1979 issue of Gun Digest.
As far as I know Ackley, Hutton and the members of ARAB were the one tslking about the .35 and .375/.444 wildcats.
Some of the Gun Writers may have met our hero Herman Bockstruck who is generally credited with the Big Bore Winchester cartridges, The Model 94 big Bore rifle and the Angle Eject feature. I’ll leave the rebounding hammer and the long take-up trigger out of the discussion.
Our Winchesters do not like the rimless cases. One in the chamber and one in the magazine is as good as it gets. Two in the magazine and a cartridge will jump the cartridge stop and tie up the action. If you tie it up don’t waste your time trying to fish it back out from under the lifter. Just pull the magazine plug, spring and follower. Then dump the cartridge out.
Here are a couple of pictures.
Redding form dies make the steps simple. I have never lost a case using the Redding form die.
A form line