Get a can of barrel blaster and a brass bore brush. Put the bors brush in a short extension and place it in a cordless drill. spray the chamber with the shotgun and choke cleaner and let it soak for 15 min. then spray it again and spray the brush. Run the brush in and out of the chamber spinning it with the drill about 25 times and then spray it out with Brake clean (non-clorinated type only) or spray the barrel cleaner in it again and use a bore swab and clean out all the crap you just broke free.
That usually corrects the problem you are having.
CPL holder since 1991, NRA Lifetime Member, DU Member, NICET certified
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