THAT is cool! I wanna shoot something with my ROA. Been saying that for 30 years, but I ain't done it, yet. I cast a Lee 220 hp that I push near 1300 fps in front of a compressed 777 load, should be enough, but I don't know about the bullet. I'm sure it won't expand and it's a round nose profile. Sounds like you may be using something a tad better.
I got my first black powder buck last season, well 777 buck, using my CVA Wolf I bought a couple of years ago. I used a Hornady 385 grain "Great Plains" minie on him, DRT, not a twitch. I don't know that the pistol bullet sabots offer much in comparison to a big, full caliber lead bullet. I've been into BP for near 40 years, but I haven't hunted much with it as Texas has no BP special hunts PRE season and the ones that they have are limited to inland counties AFTER the regular gun season which is stupid, but that's the way it is. I don't archery hunt this time of year, rather dove hunt and the skeeters can be bad along with the heat as you probably know. Our climate on the Texas coast is much like yours.