Yes 777 pellets for me were the worst and the loose powder is a little better with those primers. You could try some Rem STS primers but i doubt it will make a difference.

Use sabotladers windex patches and it not a big deal. You want to let the barrel cool a minute anyway. The bore conditioner does seem to help too and appears to get better over time vs a fresh bore.

Its either that or use BH209 powder and make sure your breach plug is clean every 10 -20 shots.