.375 Winchester (Using Sierra Bullets)
Date: Apr 30 2015
Notes from the Lab: .375 Winchester (Using Sierra Bullets)
The .375 Winchester was announced in 1978 in a Winchester Model 94XTP Big Bore lever-action carbine that featured increased steel in the rear quarter of the receiver to handle the greater head thrust and chamber pressures associated with this cartridge. Soon Ruger offered its No. 3 single shot, Thompson/Center Arms its Contender, Marlin the Model 375 lever gun and Savage its Model 99. Two loads were initially offered: a 200-grain bullet at 2,200 fps, or a 250-grain at 1,900 fps. Winchester’s idea was to offer hunters a more powerful option for its most popular sporting rifle.
The .375 Winchester case is shorter than the old .38-55 WCF and much thicker for increased strength. The .375 utilizes .375-inch bullets, while current Winchester factory loads for the .38-55 measure .377 inch (not to mention that groove diameter for this cartridge varies from .376 to .381 inch). Furthermore, the .375 Winchester operates at 52,000 CUP pressure, while maximum average pressure for the .38-55 is 28,000 CUP, with factory loads being significantly below that figure. Regardless of rumors, the two cartridges should not be interchanged, which may prove unsafe.
Using the Sierra 200-grain flat point bullet, highest velocities were achieved with IMR-4198 and Alliant Reloder 7. Very little changes in accuracy occurred using loads with each of the powders listed in the accompanying data; however, Hodgdon H-322 recorded the single tightest group.
When handloading for the Winchester Model 94XTR, cases should be full-length sized, then the case mouth expanded just enough to accept bullets. After seating bullets to the upper edge of the cannelure, a heavy roll crimp should be applied.