Here is my review of the Lee 379-250 RF bullet in my 38-55 caliber Marlin 336 Cowboy.
Lee 379-250 RF as cast with a Lyman #2 approximation alloy - Weight 252 gr. average.
The cast weights range from 254 grains for 20/1 alloy down to 245 grains using harder alloys. In my 336 Cowboy the softer alloys are showing the most promise with this bullet.
38-55 Lyman Data
10 grains of Unique will propel this bullet to just under 1300 fps in my rifle and it also appears to be the most accurate. There is enough rear sight elevator range to give me right on holds out to 200+ yards.
50 yards over Unique
5.6 grains of Unique gets 910 fps and out to 50 yards is only slightly less accurate than the 10 grain load.
My testing with 2400 was limited as the accuracy was quite poor in the loads I tried. In my rifle 16 grains would get the Lee bullet going 1511 fps avg.
16.5 grains of SR 4759 averages 1506 fps and is VERY consistent with Standard Deviations of less than 10 fps. This load is also showing some real accuracy potential. I believe this load would match the upper levels of the original black powder loadings. The load data predicts the pressure levels to be well inside the capability of the Marlin's strength and examining the fired cases appears to bear that out. Using Wind's Magi-Lube - Beeswax (5) Crisco (4) and Vaseline (1) - there is little to no sign of leading after 20 shots. I have not yet tried this load on the long range dingers but I suspect it may allow me to take at least a cover hold sight picture on the 400 yard dinger.
Recovered Lee Bullets fired into a dry sand backstop. The 20/1 alloy at 1400-1500 fps expanded the noses to more than 45 caliber (smallest) and retained a most if not all of their weight. The actual weight of the recovered bullets was greater than the cast weight as there was a good bit of sand became embedded in the bullet. Bullets were recovered 8-9" deep.
For those looking for an inexpensive general purpose bullet mold that is a proven performer in 38-55 Marlins I would recommend it the Lee. There are those that dislike the bevel base but I've experienced no issues with it.
Here is some video of it in use.