The below was generated in response to a discussion on ported chokes.
I will probably be dodging bricks that are thrown in response to this.
The below answer is my opinion based on my knowledge and belief.
Does porting reduce recoil in shotguns??
If so, how does it work?
Recoil of any shotgun is based on 3 primary factors and 1 secondary factor.
Primary factors are
1-Weight of the gun
2-Projectile weight (combined weight of shot charge and wad)
3-Speed of the projectile
Recoil can be reduced or increased by a noticeable amount by changing anyone of the above factors. Increase the weight of the gun, reduce the projectile weight or reduce the velocity of the projectile by any significant amount and you will reduce the recoil by a significant amount.
Several years ago I talked with the folks at the H.P. White lab and inquired if anyone had conducted tests to determine what the muzzle pressure of shotguns were. They told me they had not nor did they know of anyone who had.
They did tell me that they thought that the same formula that they use for centerfire rifle cartridges would hold true for shotshells, (5 to 1) that is a rifle cartridge that developed max chamber pressure of 50000 CUP would have approx 10000 CUP at the muzzle. If we apply this to a shotshell load of 12000 LUP we would have approx 2400 LUP at the muzzle. This is a very substantial reduction in pressure.
The residual gas that escapes into the atmosphere after the shot charge leaves the barrel functions as a very crude rocket engine with an incredibly short fuel burn time. This gas escaping at high speed adds to the recoil generated from pushing the projectile weight up to its ultimate velocity. However, in my opinion because of the very low pressure at the muzzle the effect on the amount of recoil generated is a small amount.
Porting the choke tube will bleed off some of the escaping gas at right angles thus reducing the “rocket engine effect” thereby reducing recoil by a very small amount. Please understand that I have not measured the effects of this on a scientific basis.