375 Ruger Question

[High Desert Hunter]

OK, so i have been getting excellent results with my bullet of 350 grains from my Accurate mold and using IMR4198, Unique, and 2400. I don't currently have a chronograph, but I figure these bullets are hitting near the 1800 fps mark with the IMR4198 loads. I have tried using slow burning powders to bump the velocity up to closer to 2100 fps, but I get keyholing with every shot. So I am wondering if my alloy isn't hard enough? Is too hard? Or if I am getting some riveting effect because the neck is short on the Ruger case. I have no doubt that if I could accurately place the shot at 200 yards, this bullet would still hammer anything NA has to offer, and it is probably pure folly to try and speed these up, but is definitely easier to make the longer shot with more velocity. I am enjoying the inexpensive trigger time, I have over 1K jacketed bullets for this rifle and 400 rounds of brass, but the reduced recoil is nice as well. So far with the lighter loads I am getting near one hole accuracy at 50 yards with this rifle, I find myself shooting it more than my 45/70, and am thinking of picking up the N.O.E mold of 270 grains that I can also cast an HP bullet of 260 grains to accompany the big 350. I never knew how much I liked the 3/8" bore until I sold my only AR at a profit to fund this Ruger. Hoping the barrel has a long life, because it gets shot a lot!