[DonVoigt]

Just some random observations for you guys.
A 9mm "carbine" can be made with a 16" barrel and function. I've constructed several.

Also "factory" recoil springs vary greatly in strength, you can selectively fit one that will fine tune function if needed.

The pressure inside the cartridge/barrel is not strictly relevant for a recoil operated action like the luger. People talk about the "balance" of the luger function and they refer to the recoil impulse which is affected by many factors including bullet weight, velocity, and the mass of the recoiling
parts(barrel + receiver extension+ sights+ any added fore grip).

The 9mm 16" barrel only functions well with the fore grip/arm that is attached to the luger frame, not one attached to the barrel itself, as such a grip adds too much weight and additional resistance if held in the hand. The original .30 luger carbines had the very "weak" flat recoil springs and needed the additional auxiliary spring in the forearm to return the barrel assembly to battery.