The secrete to NOT pushing fouling into the breech area is to use a jag that is smaller than the bore diameter by several hundreds, I use a .50 caliber jag in a .54, a .45 in a .50 etc. By using a smaller diameter jag & cleaning patch the patch does not push the fouling into the breach, but when pulled out, the patch bunches up on the jag and pulls the fouling out of the bore. Jags can be made smaller by chucking them in a drill and holding a file against the spinning jag to slightly reduce the diameter of the jag.
As for the mag-spark nipple replacement, they work well for igniting the substitute powders, but are extremely slow for reloading, and sometimes the fired primer gets stuck in the nipple and has to be pried out. I personally have never had a problem igniting the substitute powders when using a spit fire or Red Hot nipple and a standard #11 cap. YMMV