I’ve pushed lead out of barrels that were several inches in length. My M&Ps were susceptible shooting hard cast as was my wife’s 10/22 stainless which showed little evidence of cleaning before we met.
My typical solution is Shooters Choice Cowboy Blend with particular scrutiny of the chamber. That’s followed by CLP and JB Bore Paste for 20-30 passes, reloading the patch as needed. I finish with JB Bore Shine, the only thing I use in my rimfires. I rarely have need to revisit the routine, just Bore Shine with a patch followed by a nylon brush, pierce jag to push everything out, then Bore Shine on a final patch or two.
Chore Boy is a great remover but doesn’t attack the real problems; rough barrels and dried up bullet wax. The former is present in most every factory barrel with the general exception of hammer forged barrels which are generally very smooth. The latter occurs when ammo is older or stored improperly. If memory serves I last found Chore Boy all copper pads at Lowe’s.
