RE: Broadhead grain
I dont know much about arrow flight in crossbows but I do know some about arrrow flight in compounds, balance point plays a big factor in it, so does bow poundage,draw length andspline stiffness
back about 15 years ago I was into shooting compound big time and like alot of people I built my own arrows and knew quite a bit about the subject, I cant remember much about it anymore but my setup back then(and now) consisted of 30" 2114's(I forget the overall weight)and with a 55# drawit ended upthat 85gbroadheads gave the best flight and had the best balance, anything heavier and they got way goofy in flight(paper tune), so I use 85g thunderhead's
after I spent all the time and money in that setup I realised I sort of messed up though, I should have went with 2213's instead, they're a little stiffer and would have allowed me to up the poundage a little if I wanted without messing up arrow flight, but with my shoulder I have trouble pulling over 55#'s in alot of hunting situations anyway so my setup worksjust fine