Deep cleaned mine, wire brush 100 strokes (no drill), dry patches around 40 strokes, took some birchwood casey 2in1 bore cleaner on a patch passed through a few times let it set for a few minutes, then wire brushed again, then dry patched it to clean it up. The barrel was clean to the naked eye, but after running the birchwood through it, it did make it more shinnier and cleaner to the naked eye alot more fouling and deposits came out. Before cleaning I shot a 2 3/4, 7 1/2 shot, then cleaned it and shot again, it did help a touch, with TSS could be better could be worse, i would try polishing but I havent found a thread yet on just the M2 about polishing. Only took maybe 15 to do the cleaning