Rebuilding a basket case Winchester model 24 double barrel. Got everything together, and working, with one exception. When I open the barrels, the gun cocks, maybe 4 out 5 times, then the cocking slide will snap past the cocking fingers. I assumed cocking slide was worn, received new one today. Exact same size as the old one. So, I decided to drill and tap a small screw into the end, to allow cocking slide to move further forward. My drill press will not drill into that hardened steel. Any ideas on a fix for this?