I have a barrel mount chronograph, and it works, but beware. As long as you have a barrel or barrel shroud that is 5 or 6 inches long to attach it to, you are just fine. If you have a gun with a short moderator that the chronograph can't mount to and stay straight, it won't work.
Case in point. I have the Crosman 1701P. Great gun, but the moderator on the end is only an inch or so of straight material then it slopes into the barrel. No way to accurately mount the chronograph to that particular gun.
Also, barrel mounts need to be accurately placed on the barrel, or you can shoot the sensors right off.
I like mine, but do be aware of the shortcomings of the mounting system.
