Barrel indexing can be a problem...make sure the front sight is on vertical. Make sure the bolt lugs make good contact inside the receiver. Make sure magazines fit securely in place and the mag release is positive [sometimes the rivet pinning the magazine can cause fit problems, so check that any difficulty isn't being caused that way]. The safety may be quite stiff, but this can be improved just by working it a few hundred times...
That's what I can think of off the top of my head...
For a new M305 $650 is not a bad price. There was a lot of loose talk a year or two ago about prices going way up on these...didn't seem to happen, but I suppose it still could.