Ok guys loaded some 300 gr sierra jsp with 21 gr h110 oal 1.720 heavy crimp. Just came home from the range started out with .44 specials than some light magnum than the big stuff. Grouped nicely stout recoil not something for a full day of shoot. I was at our indoor range and soon we had it all to ourselves.

Groo here
The 300gr bullet in the 44 N frame is one of those cases where the cast version is better than the jacket one.
The load you are using is on the top end,,, it would be easier on the gun
with a cast bullet.
When the 300+gr 44 mag load started to get going,
N frame smiths were found to be somewhat under sized and
had problems shooting large numbers of them [pre-durablity mod]
I used Red Hawks, Black Hawks, colts and Dan Wessons instead.
If you feel the need, use cast, and start at a 90% loading to the
base of the bullet of AA1680/ww680 powder.
Bullet speed will only miss H110 by 100fps or so and pressures will be
less, easer on the gun.