Depending on what projectile you shoot, sometimes it is necessary to swab the barrel between EACH shot. I know that really stinks but if you want to shoot a certain projectile then you have to play by their rules. I am not sure about the Powerbelt issue Triple Se7en is talking about, but he sure knows his projectiles...

To change this problem, sometimes just changing powders will allow you numerous shots. With Pinnacle Powder I was able to shoot 12 T/C mag express 240 grain XTP's without swabbing. Normally I might make three shots before needing to swab. I think I could have done more, but ran out of the projectiles, so I swabbed the barrel before shooting a different projectile.. Triple Se7en and Pyrodex seem to be the worst powders for having to swab. Triple Se7en because of the harder fowling it produces and Pyrodex because of the massive amounts of fowling it produces...
Goex is another one, but all us Goex shooters know that the powder fowls out bad... We just like the smoke and the stink..