To me, increased pressure can only speed up the projectile, creating more energy, and the same amount of increase in recoil.
Several conditions must be understood in this assumption.
First is of course that movement does take place. If, as rocketman stated, the projectile were "Secured" so it could not move the maximum pressure that charge of powder could produce would be generated with no motion of either projectile "OR" gun.
Under ordinary conditions though the projectile will start to move down the bbl & the bbl will start to move in opposite direction in proportion to their weights.
A further condition, velocity of the projectile (along with that of the gun) can be increased in two ways 1; an increase in pressure, 2; an elongation of the time that pressure is applied.
It must be understood that bbl pressure when a projectile is launched is not a constant, but in the form of a curve. When this is understood it becomes quite obvious that "Max Chamber Pressure" is not directly related to the velocity of either the projectile or the gun.
One often sees ads stating that for $XXX a person will perform operation on your gun bbl which will simultaneously give you increased velocity & reduce the recoil. Friends this is total "Unadulterated HogWash". When firing the same identical load from the same gun, with no external modifications, anything which can be done to its internals that reduces recoil, does so at the expense of ballistics, it'd just that simple.
That "Friction" said to be reduced thus allowing exra velocity with reduced pressure was also giving an alternate "Forward Push" on the gun. "IF" a reduction of friction does indeed give you an increase in velocity, it will aslo give a proportionate increase in the rearward velocity (Recoil) of the gun, regardless of any change of pressure.
Again Recoil is directly related to the wt & velocity of the ejecta, Not to Pressure.
The wt of the powder gasses & their increased velocity as the projectile clears the muzzle is also a factor, & the only one not readily calculatable. This can normally be estimated with reasonable accuracy by adding about 25% to wt of powder charge for a shotgun, about 50% for average centefire rifles & about 75% for magnum rifles.
Reports of either "Reduced" or "Brutal" recoil from internal bbl conditions unaccompanied by a through examination giving full ballistic particulars of the firing under identical conditions existing to those while actualy firing from the shoulder, is best regarded as anecdotal & thus disregarded.
