Pressure diff from choke?

[LBL]

Originally Posted by Dean Romig

But the question remains - what accounts for the 100 fps difference between chokes?


I believe it is only the constriction under the same pressure.
Put a nozzle on your garden hose without changing the pressure and the water stream goes faster and farther than without the nozzle. Physics 101.

.

I think Dean’s “Physics 101” explains the velocity difference between the Mod and Full choke barrels in firing these tests of a new reload recipe. As the concern re older Parkers is pressure, and pressure is only relative to velocity in the same constriction (and undoubtedly other barrel attributes) that raises my last question again, if anyone knows:
What choke (and other barrel attributes eg length?) is used for the fps specifications published for shotshell ammo and reloading recipes?

Further: Are there perhaps any formulas for translating shotshell velocity published specifications of a given gauge and shot mass into the pressure to which the gun is subjected? (Seems like pressure could be a more consistent specification on commercial shotshells than velocity.)

Thanks again for your consideration of this topic.