The Glock 21 ans 22 are NOT the same frame. The 17 and 22 ARE.
I realize that, but the comparison would still be more fair since there is only a 3.9 oz difference between the loaded weights of the G21 and G22, while a typical 1911 weighs more empty than the G21 does loaded (about 13 oz greater in empty weight, which dominates when ammo is low).
It boils down to physics. Every action has an equal and opposite reaction. That is where recoil comes in.
Recoil is essentially measured in foot-pound-seconds.
If the two rounds that are fired have equal force (measured in foot-pounds)
Foot-pounds are a measure of energy, not force.
Plain old pounds are a measure of force.
and the weapons fired are equal in weight (thus equal inertia), and they are both of the same type (thus spreading the force of the reaction over the same period of time, IE, a weapon with springs like an autoloader spreads the reaction over a longer period of time, as the springs absorb some of the force) the recoil will be the same.
A good example will be the Sig 229. Available in both 9mm and .40 S&W. Same type, same weight pistol.
Two standard loads:
Now fire a 9mm 147 grain at 1,210 fps. 474 ft-lbs
Then fire a .40 cal 155 grain bullet at 1,175 fps. 475 ft-lbs
The difference in recoil will be indistinguishable.
Correct in theory, however this is a good example of where theory diverges from practice because I doubt that such a 9mm load exists. Find a 9x19mm load that can launch a 147 grain bullet at 1210 fps and prove me wrong.
More realistically, an extremely hot 147 grain 9mm+P load may equal a run-of-the-mill 180 grain .40 S&W load in energy, and I wonder which would feel snappier. A hot 115 grain 9mm+P load will far exceed an ordinary 180 grain .40 S&W load in energy, and it may feel even snappier if energy and acceleration are what cause this phenomenon.
Your son is wrong, you are right. Tell him go ahead and learn this lesson, it will save him some trouble in life. At least that has been my experience, dad was/is almost always right and listening to him would have made life easier.
On the other hand, my dad, who was a Vietnam vet, told me that AKs could fire both 7.62x39mm and 5.56x45mm ammo interchangeably--the enemy could pick up our ammo and use it against us!
He probably heard the rumor from his buddies because he didn't know much about firearms, at least in a technical sense, and didn't seem to believe that the enemy simply picked up whole M16s instead (probably never accepted the theory because he didn't think that the M16 could actually shoot--he carried an M1 Carbine instead). Dad was a lot smarter about other things like how to handle money, but firearms...EH!
