If most are the same as mine I would say you would be pushing it at 20M.
I have used it on vermin out to 15m with some success - and it is certainly accurate enough. The trigger is heavy - but can be lightened by polishing the sear and trigger contact points.
If I am honest - I usually revert to my AA410K over 15M - but the ratty is easy to bring up - and great at short ranges.