I had one and just like you said- erratic. One range time would produce good groups. Next time- same loads and it shot like crap. Got it primarily as a youth gun, but no way I'd put a youth hunter behind that with those results.
You can try fiddling with the forend adjustments. I thought that helped some for a while, but not really.
Also, that gun seemed picky as hell about front rest placement when shooting.
Finally had enough and sent it down the road. Had one in 450 BM before that. That one was similar, but also had the problem of a rimless case which does not mesh well with their extractor setup.
