I was using Magtech's .44 SPL load and my 21-4 is shooting about 12 inches high at 20 yards! I see there is a roll pin in the front sight blade; is the blade replacable? Not that I would attempt it; it would be a gunsmith option.
I think this load is called their "Cowboy Action Shooting", from memory it is a 240 gr flat-nose lead at 760fps. I considered the load but concluded that a heavier load would make it shoot even higher, right? More recoil, more muzzle rise?
I seem to recall some early 21-4's came from the factory sighted incorrectly. If yours is one of them, S&W should fix it for free. Might be worth calling them.
FWIW, the .44 Special is famous for printing high with either slower than standard loads, as well as slower than, and heavier than, typical loadings. Every one of mine always has? If there were any available, I'd be tempted to try a Remington 246 grain LRN factory load at the same distance and see what happens?
YMMV?