Im using my muzzleloader to deer hunt this weekend.. I typically shoot 250 grain but my local shop doesn't have any which got me to wondering.. How does the grain effect the shot.. Will going from 250 grain to 245 grain or 295 grain have a big effect on the accuracy.. Or will it just have an effect on how high or low its shooting? Thanks

It could very well effect the accuracy. Some rifles just don't like some bullets. All you can do is test the bullet. See how it groups, and how well the rifle handles them. After that its deciding whether or not you want to hunt with them.

Like Cayugad said, you have to try them and see. You could have 3 bullets that all weigh 250grs and have each one of them shoot totally different. Even a .44cal bullet that weighs 250grs vs the same bullet in .45cal will shoot different.
Bottom line I'd just never assume just because the bullet weighs 250grs and that's what your other bullet weighs that they'd both shoot almost the same. I'd never ever go hunting befor I went to the range and tried them out and sighted in my mler with them first.
Good Luck!
(BP)