RE: different grains?
J in GB, I was trying to find my info as I shoot the 240 and have tried the 300 XTP. I believe it was 2-3" low with 100 gr of Pyro(pellets). In my case it shot lower and my groups opened marginally as I recall, not sure why but in any regard I have stuck with the 240 for my deer medicine.
Best to shoot em and find out