Winchester chambered the .375 Winchester cartridge in its lever-action Model 94 XTR for only a few years during the late 1970s. Marlin, Ruger and Thompson/Center also made their own very short runs of .375s. These relatively few .375 Win. rifles have reached collector status after being out of production these many years, and bullets and brass for handloading them is limited.
Northern Precision Custom Swaged Bullets has projectiles for the .375 covered though, offering 180-, 200-, 225- and 250-grain Flat Tips. Lead cores are cast for the bullets, which are inserted into a thin jacket for rapid expansion or bonded in a heavy jacket for near-total weight retention. The bullets are also available with a spitzer nose for single-shot or bolt-action rifles.
Cases for the .375 Win. are difficult to find and expensive. Fortunately, years ago, I bought several bags of Winchester brass with my .375-chambered Model 94. Starline cases are occasionally available. Acceptable cases can be made by expanding the neck on .30-30 Win. cases. Lots of lubricant is needed on the inside of the case necks, and expanding them first on a .35-cal. expander ball and then a .375-cal. expander ball eases the forming process. Expanded .30-30 cases are about 0.120" short of the 2.010" trim length of .375 cases. These formed cases should only be used with low-pressure loads, as .375 Win. cases are thicker to withstand the .375’s higher pressures.
Reloder 7 has produced the best accuracy and velocity with every .375 jacketed and cast bullet load I’ve shot over the years. Fired by Reloder 7, the Northern Precision bullet turned in a standard deviation of velocity of 7 f.p.s. over nine shots, and five groups at 50 yards varied in size from 1.32" to 2.82".