Looking at loading some blank 12 gauge shotshells with black powder for use in a single shot style shotgun (break action). Most recipes call for FFg (6 oz, I believe). Newer shotgun (about 3 years old).

Can I use FFFg? For whatever reason, FFg seems hard to find locally, but triple F is not. Do I need to modify the load any, or should it not be a problem since it is a "blank" with just an overshot card and a roll crimp?