I have worked up some loads for the converted Ruger #3.

CAUTION: These loads exceed CIP standard pressures for .375FL NE 2-1/2" cartridge. Use only in modern rifles designed for high pressure cartridges. These loads produced the listed velocities and pressures in the test rifle. Results in other rifles may be different. Follow safe reloading practices.

WARNING: These are high pressure loads. Do Not use these loads in guns and rifles originally manufactured for and/or proofed for standard velocity .375 FL NE 2-12". Disregarding this warning may result in damage to your rifle and serious injury or death of you or others.

Conditions:

Ruger No. 3 rechambered from .375 Winchester to .375FL NE 2-1/2"

Barrel length 22"

Pressures taken with RSI strain gauge, W-R ammo used as reference

Temperature was 57 degrees F

Elevation 450' ASL

Loads using 300gr old style Winchester Silvertip.
All bullets were seated to lock into the outer crimp ring. Cartridge OAL 3.21".

49.5 grains of RE-17 -- 1,943 fps, 41,820 psi

51.0 grains of RE-17 -- 2,062 fps, 45,501 psi

52.4 grains of RE-17 -- 2,091 fps, 46,591 psi (compressed load)


Loads using 320gr custom rounded tip bullet, .030" jacket for low velocity expansion. This bullet is very similar to the original 320 grain bullets made for this caliber. Bullet length is 1.275" (almost the same as the Silvertips). Cartridge OAL 3.21"

36.5 grains of IMR 3031 -- 1,680 fps, 34,922 psi

40.7 grains of IMR 3031 -- 1,847 fps, 40,391 psi

49.5 grains of RE-17 -- 1,918 fps, 41,835 psi

51.0 grains of RE-17 -- 1,928 fps, 42,117 psi

52.4 grains of RE-17 -- 1,954 fps, 44,652 psi (compressed load)