Cleaning Barrels

I remember when shooting cast lead bullets out of a 357 revolver that I had a problem with lead building up.
Slugs would be similar to cast bullets. We shot them at higher velocity and I’m thinking that might be a factor in this. 
Now the next question why not pellets. I suspect at high velocity they might lead up as well.
Just a guess

Well you won’t get atomization like with an explosion, but you will get small fragments in the lands that do build up. 
 
Been a long time since I shot cast bullets … back in my old powder burning days. If you are picking up a lot of lead, you might want to find out what they are made of and decide from there how fast you want to shoot them. I used to make mine out of linotype and wheel weights and got all the contaminates out with bees wax. I could throw those down range at close to 1300 fps without any leading … they were VERY HARD and if they hit something hard like metal they would crack and break into pieces before they would mushroom. Used softer lead for slower velocities like from a .45 acp. 

Sooo I would say if you are picking up excessive leading find out what the slugs are made of and adjust velocity accordingly.
 
I'm not a slug shooter, but used to cast a lot of bullets for metallic cartridges. I assume air rifle slugs are soft lead, maybe almost pure lead. If so, I would expect them to foul like crazy at higher velocities. And, given the larger bearing surface, I'm not surprised that it is a challenge at lower speeds too. And I expect the use of poly barrels makes it even more challenging. Sometimes, it's nice to be a low power, short range, pellet kind of guy. 
 
I used JB Bore paste after about 100 round
1590617518_19692385215ecee5aeedb589.50152535.jpeg
s in my new FXImpact STX. Pulled lots of lead flakes out of the rifling. Accuracy is awesome post cleaning.