This really fits most all semi auto handguns. On Guns and Ammo TV just a few minutes ago I caught the tail end of story on hand guns and recoil etc. Upon firing before any unlocking, of the barrel, and unlocking the slide, and rear movement, there was a vertical high pressure escape, of gas through the small spot, in the top of the slide. I think the gun was a Glock; at any rate, it was black, square, and plastic. We've all seen handgun ammo cases with black smears down the side of the shell casing and dirty guns as a result. It means to me not enough pressure or the brass case to expand enough to seal at the mouth of the cartridge. We've seen it on revolvers too. I don't remember seeing it as much in old nickel .38 cases which are thinner, as much. I think it is party the result of marketing forces, for lawyer proof safety with lower pressure and lower velocities. In my .357 my 125 grain loads sea and there is no back smear along the shell casing from burned powder. Factory loads there are smears and toward the thinner part of the chamber next to the cylinder. In my 9mms I don't see much to any in hand loads or in NATO loadings. I looked though a pie of 9mms a while ago and some, the Winchester cases have more smear of carbon. I don't like the idea of escaping gas in my guns. I have had pieces, of whatever, hit e in the face and on my arms and hand over the years. Never caused any problems but a bit of irritation mostly. So most of my loads are hotter than factory, and data from old manuals. And I see less blow by. Are today's guns so weak that the weak loads from factories, and in current manuals is really called for or are Lawyers and bean counters the reason? How do you establish your loading data or do you, as most of us do just follow the manuals ideas or go from there.