My hunting buddy is having a problem...He changed strings on his longbow and now really slaps his arm...brace height is the same etc but we just cant figure out what he is doing

Try putting the old string back on for a few shots just to see if it really is the string

If it is really the string, only thing thatd make it change besides NP is the weight at the serving making it carry further.Are the arrows the same a lighter arrow will have more string follow too

Good luck

The only thing was he changed the string? is he torquing the bow? holding is wrist or arm to stiff and straight?

If he went from a low-stretch string (FF, TS1, D97, etc) to dacron that can happen.  There's a reason I put the low-stretch materials on my selfbows!  :D

If he's right handed, take a half step forward with his right foot.

It's probably what Jeremy said.  The old string is low stretch and the new string is B50.

Put the old string on and see if the problem is still there.

Mike

Jeremy is most likely right. I have trouble with any bow shooting Dacron with my big forearms. If I shoot FF I have way less trouble. Shawn

It's all about dynamic elasticity.  Typically, less stretchy/creepy fiber will produce small string sine waves on release than the stretchy Dacron stuff.

Thanks guys we will see what we can get fixed got a hog hunt in a day and a half hope we get er worked out by then thanks for the help!!

Agreed.  My Dacron string was slapping.  Switched to FF, and the problem went away.
I also agree that if his problem continues, bring his right foot forward and open up his stance a little.  
Good luck on your hunt!

Yep, what Jeremy said.  Probably different material...Van