Oh yeah it killed the rat instantly, well apart from a tiny bit of twitching, but thats normal, yeah i'll probably just start shooting from standing/rested because then if it penetrates it will just go down into the mud at that angle.
Use .22 RWS Super H Point in AA410, no problem with accuracy out to 20yds, furthest I've tried! Instant kill with headshot plus 1 I hit in the body pegged out without a squeak!