I have the same gun. I recently loaded up 17grns of 2400 w/ the 300gn sporting handgun bullets. This is published MAX load according to Nosler's #5 manual at 1313 fps. Also, I'm using WLP primers, but am switching to Federals when the WLPs run out.
H4227 20.0 1312 38,600 CUP
H110 19.0 1325 38,800 CUP
LIL'GUN 17.7 1280 37,600 CUP
Longshot 9.5 1071 34,700 CUP
HS-7 14.0 1214 37,300 CUP
HS-6 13.0 1214 37,900 CUP
UNIVERSAL 9.6 1113 38,200 CUP
HP-38 10.0 1149 38,100 CUP
TITEGROUP 9.6 1186 38,400 CUP
Depends on the firearm my friend. If you look at Hornady's Manual they quote 19.9 gr as max with their 300 XTP. My 44 has had no troubles with 20 grains of said powder. Primer pockets are tight after 10 firings or so and fired brass slips right out of the chambers.
I will admit though that lately I just use 23 grains of LILGUN with 240 gr Nosler HP's for everything.
:lol:
As far as using XTP data for other bullets start at 17 or so and work up.