WHAT KIND OF RECOIL DOES THE 450 MARLIN HAVE WITH THE 15 INCH BARREL WITH BREAK ON IT? I'AM THINKING 20LB

Well since nobody else is saying anything I will. I guess you are talkiing about a Encore.

Don't have a Encore or a 450 Marlin but do have a XP-100 in 458X2 American from SSK.

So here it goes with the 300gr at 2150fps it is not to bad.With the 500gr bullets at 1650fps it is getting rough not to bad but you don't want to shoot all day with them.The 450 Marlin is not chambred to shoot the 500gr bullets I think.This is with a 13" barrel and SSK brake on it.