The older domed NFPJ plug was supposed to reduce the fouling but ive never tried one. I have one but never tried T7 in mine yet. The FPJ plug works fine but it is dirtier and the flash channel is small. Keeping it clean is the only issue with it IMO.

I prefer the new NFPJ conversion the best regardless of powder and preferably the original Lehigh GenII which is no longer available. My main reason is because they are so clean and the flash channel will need less maintenance.