Ah well, so much for the various arguments that are unrelated to the original question.
4f as a main charge in a pistol is, in most cases, acceptable. It is also acceptable in reasonable amounts in small caliber rifles such as a .32 cal. but, I would never use it as a main charge in anything much larger than a .32 cal. rifle. Some would, but not me. It develops a pretty high breach pressure and could be sufficient to over pressure a larger caliber barrel. Having said that there were some cases in which it could be used as a main charge, if it were me, I'd reserve it for use in a flintlock pan and use 3f for my main charge in anything up to and including a .54 caliber. For shotguns and calibers larger than .54, I'd use 2f. But that is just me. I like to err on the safe side.
I know there are experiments where 4f was used to excess in a larger caliber barrel with no apparent ill effects. But, wisdom and common sense says not to do this. I wouldn't do it, I do not wish to risk my limbs, my life nor my gun just to see if 4f will work in my gun as a main charge. But, like I say, I prefer to err on the safe side.