The crud ring relates to shooting sabots or powerbelts in dry barrels from inline rifles.

Triple Se7en makes a good point here, using primers that are on the "cooler" side do tend to produce less
buildup in the breech area regardless of which powder you are using.

Roundball & Cayugad make a good point as with Goex black powder, the breech area buildup inside the barrel is softer and if you are shooting patched/lubed roundballs, allow for multiple shots without the build up becoming an issue.

I like Winchester Primers, which are not as hot as several other mfg's.

There is more buildup down near the breech area with any powder.

In my experience, with 777 this build up (or Crud Ring) phenomena is more difficult than other powders as it seems to be much harder and crustier than other powders.

It becomes an issue if you are not swabbing between shots, as loading sabots will eventually become impossible.

This is not to say that 777 is not a fine synthetic powder, it is. Goex is also a fine traditional powder.
777 (Like everything else) has it's own characteristics that often require either procedure or equipment adjustment to optimize or refine it's usage.

It was looking like fisticuffs in here for a few threads. [:@]
Hopefully Triple Se7en and Roundball can be amigo's again.