Absolutely Correct Larry;
No currently known propellant suitable for use in shotgun loads will reach its peak pressure outside the chamber of the gun. Fast & Slow are relative terms. Even the slowest of shotgun powders are Fast relative to rifle powders, & the slowest of the rifle powders are Fast relative to powders suitable for large artilery pieces etc.
If you compared the pressure curves of say 7625 & 700X, both pushing 1 1/8oz of shot to 1200FPS you would find the following; The 700x load would have the higher max pressure while the 7625 load would have a higher retained pressure at the 10" mark. Both however would have hit their peak (max) pressure within the confines of the chamber likely not more than Ľ" apart.
