I got an onld 870 wingmaster. Got a decent deal, but new it was in serious need of cleaning. Get it home, pull it apart and the trigger group is all sorts of cripudded up. Clean it with a brush and various cleaners as best I can, but pulling the hammer back still feels gritty. Feels like someone dumped sand into the thing. Short of complete dissassembly of the trigger group, which I have heard is quite tricky, are there any good methods for a more thoroguh cleaning?