What size game will you hope to take with this?
"Limiting" yourself to factory ammo (which really isn't any limitation any longer as there's a virtual pethora of factory ammo) is more an exercize of deciding what will work for what you hope to cleanly kill, picking among the several offerings, & bench-testing to see what shoots best.
If you're gong after "just deer," the WSP 150s that "shoot best" will do the trick for you.
Curious as to why you'd want to use BTs & what is "shoots best" so far re group size between the ones you've tried .... nothing intended, merely curious.