Check with Vic Havlin for all things Mossberg.

www.havlinsales.com

The PITA factor on a lot of Mossbergs is that the forward bolt placement impacts the receiver grooves for scope mounting. Vic sells a set of 1" bases that mostly alleviates the problem, the rear base is a cantilever style, but it is something to take into account when you're looking a Mossberg rimfire 'cause it costs $38.

I have a 640M with this mount and while it works and makes the rifle more useful than it would be without a scope installed, I don't love it.