IMR-7383 in the .50 Alaskan Remington Rolling Block Rifle

I've had so much good luck accuracy wise using the .50 Spotting Powder IMR-7383 in all sorts of calibers I thought I'd try it in my .50-110-750 Smokeless PowderRemington Rolling Block Rifle.
I've had really good results shooting the 50 BMG projectiles using IMR-3031 that I thought I'd try this powder with a heavy cast lead bullet.
There is a bullet trap in my reloading shop so working up a load is just a few steps away from the loading bench.
After crunching some numbers I found that a good starting point would be 40 grains of IMR-7383 under one of my cast 660 grain, .512 flat base hard lead bullets.
This proved to be OK but on the weak side. Lots of unburnt powder. I increased the load to 43 grains and got a better burn,but still some unburnt powder grains in the bore.
46 grains was better still with a couple of stubborn grains refusing to ignite. A load of 48.5 grains burned cleanly and recoil was manageable, as if I was shooting a 12 Gauge slug out of a riot shotgun. 50 grains was max load with unpleasant recoil with this rifles steel butt plate. The 50 grain load was being compressed to where any more powder my be in danger of a pressure spike, which with this powder you want to avoid at all cost.
I'm hoping that this load will do well at long range. I fired five rounds into the bullet trap;afterwards cleaning the rifles bore. No signs of leading.
Estimations show the bullets to be around 1,600 fps. Not laser fast,but not really poking along either.
I built the rifle to shoot surplus .50 BMG pulled projectiles and these days the cost each can be a buck or more. So,cast is a viable way to go for me,
Here is the case and bullet. Above is a 220 grain .30-40 Krag bullet.
Attachment 223773

That ought to harm anything that gets hit by it. It'll probably go lengthwise through an elk or most anything else, so there's no need for more speed. I am surprised at how fast you are able to get it to go in that straightwall case, but then again it does hold quite a bit of powder.