Use Hodgdon data for a 1 1/8 oz load in an STS hull with a Figure 8 wad and 18 grn of Clays powder as one example:<ul><li>using a CCI primer the velocity is 1145 FPS<li>using a Fed 209A primer, 18 grns would produce substantially higher than 1145 FPS because that's what you'd get with just 16.9 grn of Clays<LI>Winchester and Rio primers would both produce higher than 1145 FPS with 18 grn. because they both produce that velocity with just 17.5 grn of powder.</UL>
An important point to note is that the primers that would produce the higher velocities will also produce higher chamber pressures... in some cases high enough to exceed the max limit for a 2¾" 12 gauge chamber.
Willie nillie primer substitution is an inordinantly bad idea. Here's why.
Primer substitution affects not only velocity (a performance issue) but more importantly, chamber pressures. Those pressure differences can be SIGNIFICANT. The URL above is a link to some test data documenting examples.
I've also seen test data for reloads where the only change was crimp depth. Pressure variations caused by different crimp depths ALONE can be as much as 2000 psi.
Research old ts.c threads and you'll find "experts" claiming any random combination of junk you sweep off your loading room floor will make a perfectly good reload. It aint so.
You'll never go wrong using tested data published by component manufacturers.
<blockquote><I>"How much crimp depth variation to cause 2K increase in pressure?"</I></blockquote>...depending on the components involved and from the P&V tests Downrange did for me, about .030" ought to do it.