i have the (same one?) boresighter. It comes with various adapter and mine can fit inside a .22 cal barrel. i sighted my ak 74 (romak 992) and my ruger 10/22 with it.
The tubular body should be able to fit inside .22 cal barrel. I did have to use one of the adapters and press/ screw in the adapter to "swell" for a snug fit.
hope that helps