I will be using the Parker 275 this year in one of mine too. They do very well at sub speeds and hold up good enough at smokeless speeds. The thin jacket and soft lead core seems to make them obturate better than some bullets and IMO that can help groups a lot, even in a sabot. They were more intended for sabotless 45cal shooters but work great in sabots too.

Good luck and let us know how they performed for you. Most people that have used them for deer really like them. You can get them occasionally under the Traditions brand when they have web specials at a huge savings. I paid about $9/15 during the last closeout sale. Im not sure if they will offer them again at that price since they are now sold out.