Two issues I can think of right off hand are that the paralax will not be right. A rifle scope will most likley be set to 100 yards or so, unless it is for a rimfire, then it might be 50 yards. I don't know if the crossbow scopes are set lower or not. I would think they would be since your shots would be inside of 40 yards or so.

The other issue would be the recoil. Sort of like putting a regular scope on a high powered spring air gun. It can destroy a scope because the recoil is reversed and the scope is not made to handle it. I would think any air gun scope would work well on a cross bow though.

That being said, I had a barnette 150lb compound cross bow years ago, maybe '85-'86 or something. I had a run of the mill bushnell on it and never had anyproblems with it. Probably a 40 dollar scope I got at Kmart or something. I was only like 18 or so at the time. It worked ok and never broke. I sold the cross bow after a little while and bought a savage 30-06 and put the same scope on the rifle with no problems there either.

However I put a really nice 100 dollar scope on a high power pellet gun once and it ripped the reticle right out of it on the third shot! A cross bow would have the same type of forward recoil so it is a possibility it could happen.

Take a look at a Red dot scope if you can use them, they work pretty nice on a crossbow. They also make scopes with different aiming points in them especially for crossbows. It would be simular to a multi pin sight on a bow. I don't beleive they are adjustable though, I think they are factory set. I believe Horton puts them out? So they are calibrated for the speed of thier bows I would guess.

Good luck,
Paul