What your getting is a crud ring building up from the Triple Se7en ignition. If you are not swabbing between shots, you have a couple choices.. you can swab the barrel before you load and then get the second shot down the barrel. You can go to a thinner sabot and maybe get the second shot loaded without swabbing. You can change powders and go to something that does not leave a crud ring. Or you can go to a secondary back up projectile that you can load if need be in a hurry like a powerbelt, ball-et, or conical..

Its hard to just say, yes this will work. These are the things I would try, starting with a good swabbing of the barrel before loading the second shot..