I have read comments made by Bart B that said using the same rifle and ammo but changing shooters could cause a 50 fps change in velocity. I think he should know. Now that I've thought about it, I think he said 100 fps.
Just verifying I have seen his posts on this. Actually been wondering about his lack of posts recently.
I missed too many physics classes as well, and the ones I had were a long time ago.