The plastic does seem to build up to make loading a little more difficult, factory UBC treatment and all. Only time will tell if the FPB guilding metal jacket will foul at all.
The people I know that use saboted shotgun slugs tell me that plastic build-up is a problem for them, with accuracy falling off after relatively few rounds. It's really only a factor at the range unless you get in a running gunfight with your deer.
