It's a little fast for round ball especially if loaded up to higher velocities but the REAL bullet should do pretty well in this. I would suggest you try a few loads starting about halfway between the lowest & highest, working up from there to see how groups hold. That is the best way to tell. If using round ball I would try a slightly smaller ball with thicker patch material ( like a .490 instead of .495 ) cause the thicker patch will hold up better in the rifling.
Without doubt though these faster twist newer rifles are designed for the 250 to 400 grn "buffalo" bullets.
I went through my loading manuals and I did find the CVA Stalker in 50 cal with a 28" bbl & 1:32 twist. It had 3 seperate load data entries. (Gun Digest Black Powder Loading Manual #4 )
#1 was for 490 Rd Ball with loads from 70 to 90 grns of 2f & .015 patch
Muzzle Velocity from 1689 to 1868fps & Muzzle Energy of 1121 to 1372fpe (respective)
At 100 yds 980 - 1045fps & 378 - 430fpe
#2 was 90 gr 2f w/ 225gr CVA HP Sabot
Statistics: At the Muzzle, 1649fps - 1359fpe
AT 100 yds 1319fps - 869fpe
#3 was 70 to 90 grn 2f w/ 385 Buffalo Bullet using 'Slick Load' lube
Statistics: At the Muzzle, 1310 to 1383 fps & 1467 to 1636 fpe (respective)
AT 100 yds 1051 to 1106 fps & 945 to 1046 fpe
This is the best info I can find for you... "DOC" Jim R. Shooting BP for over 40 yrs