Somewhere I read a quote from a Remington lab report circa 1930 that dealt with velocity increase as choke increased. The report noted slightly increased velocity with each increase in choke (I recall 50 fps for full choke). I hope someone knows the article I'm referring to as I have been unable to find it in recent years. That is what theory predicts, although said theory doesn't address a semifluid such as shot. The increase in velocity comes via reducing pressure over the length of the choke section.

Following is my personal theory as to how choke works (neither proven nor disproven). The mass flow rate from chamber through muzzle exit must be constant. The exit velocity is the sum of velocity at choke entrance plus velocity gained within the choke. Shot column internal pressure at choke exit is choke entrance pressure minus pressure lost across the choke length. Shot pellets at choke exit experience two forces acting on them that cause pattern formation. The pellets all have some deformation from contact with neighboring pellets (lead has a low spring constant, but does have ability to rebound from small deformation). Any of said deformation that is not permanent will return toward spherical and impart some small velocity to the pellets. The part of that velocity that is "sideways" will tend to move the pellet off the center line of the pattern. Likewise, there is pressurized air entrained within the shot column. At muzzle exit the air exits the shot column, some "sideways." This sideways air movement farther "blows" the pellets off the centerline. Thus, most every piece of shot has some sideways velocity.

A pellet that is one foot off centerline (outer fringe of a 24" pattern) at one tenth of a second of flight had a sideways velocity of 10 fps. That is on the order of 1/100 (0.01) of the forward velocity. Seems to me to be a reasonable amount.

The full taper bore would lose most of its choke effect due to friction loss from chamber to muzzle. If you tack a choke taper at the muzzle --- well, what is the point of the taper bore?

Keep in mind that shot pellet transit of the choke is an orderly event. Pellets do not "slam" into the choke. They flow through it.

DDA

Last edited by Rocketman; 10/17/21 12:11 AM.