WhelanLad,
I recall a time during the late 90's/early 2000's when there were a number of WLR primers that would fail to fire, both in handloads and factory ammunition. Several people I know experienced this problem too. Winchester got that one figured out and quickly fixed; but for a while I only used Federal primers for loading my 375 Win ammo.
I generally stuck to the 220 gr Hornady FP bullet. I did try some of the heavier bullets once, but found that they shot so much slower that the bullets were about 3' feet low at 100 yards as compared to the 220 gr bullets, that I did not pursue the loading any further. The 220 gr bullets worked well on black bear, moose and caribou, so I left that load alone in my Marlin, and also use the Winchester 200 gr PP ammo, as they shoot to very close the same point of impact in my rifle. Sorry, but I never did chrony that handload in my rifle, but it should be close to 2000 fps according to the old Hornady manual I got the load data from (they used a Winchester Big Bore for their load development).
Now that I again have another Winchester Big Bore in 375, I am going to try the Sierra 200 gr FP bullets in it, along with the HSM ammo loading the same bullet, that I have on hand. May get to the range on Monday to try it out, along with my '94 XTR in 30-30.