You are fouling out....
Heat??? I guess, maybe...but heat is not the real problem. Heat causes the fouling to harden...it is the FOULING that causes the foul-out.
We really see this foul-out with the blackpowder cartridge rifles.The barrel will get so hot you can't touch it and accuracy is NOT hindered as long as you keep the fouling moist. Heat will keep you from being able to moisten your fouling so it has to be wiped out.
It takes more than one dry patch to keep your accuracy. Try two wet (moist, not dripping wet) patches and two dry patches between shots.
Maker of Horse Tack and Cowboy Gear.
Mister, why do you carry a 45? "Cause Sam Colt don't make a 46."