I have a superior x short 500mm that i shoot a mag (28) or two of slugs every once in a while and the last tin of H&N 23 gr (?) had a white coating like lithium on it. They shot great slug on top of slug to 48 yards, and when I switched back to my usual 18 gr pellets they shot better than they did before the lubed slugs! I think the coating on the H&Ns had something to do with it. I also had some uncoated 23 gr NSA that afterwards shot great as well. So the lube or coating does make a difference and it does stay in the bore for a while. Yes the slugs shot good before, still slug on slug (a flier here and there) but not as repeatable as the lubed slugs, they were more consistent.
oh, this is with .22