Chinook:
The difference in the two pistols is in their recoil design. There have been treatises written on this subject, but there are basically two types of recoil design in semi-automatic pistols: (1) blowback, and (2) locked breech. There are several variations on each one of these designs, and some pistols have aspects of both. The subject is extremely complex, but nearly all semi-automatic pistols can generally be divided into the two categories -- blowback and locked breech. That being stated, the Seecamp is a blowback pistol while the Rohrbaugh has a locked-breech design.
Expressed generally, in the blowback system there is no positive lock between the slide and the barrel of the weapon. The mass of the slide and force of its recoil spring (a double spring with the Seecamp) act to keep the breech closed. The expanding gases from the fired cartridge overcome this inertia and "blow back" the breech. The breech must be kept closed until the round has left the barrel and gas pressures have subsided. To remain practical this system is limited in semi-automatic pistols to relatively low-pressure rounds such as the .22 LR, .25 ACP, .32 ACP, and .380 ACP. While a larger caliber blowback pistol could be designed and produced, its felt recoil would be extreme and the recoil spring would have to be so strong that a person of normal strength would have difficulty manually operating the slide. As a result, semi-automatic pistols designed to use the larger and more powerful cartridges, such as 9mm Luger, .40 S&W, .45 ACP, etc., will employ some form of locked-breech action. In such a design, the slide cannot move back until the barrel unlocks due to the initial recoil impulse. The recoil spring in such a weapon needs only to be strong enough to cycle the action once the breech is unlocked. A significant amount of the recoil impulse created by the fired round is dissipated in unlocking the breech of the pistol. Hence, a blowback pistol chambered for .380 ACP may produce more felt recoil than a 9mm pistol with a locked-breech system.
If I have made any errors in this post, some of our Forum members with engineering or physics backgrounds should be able to correct them and explain the concepts in better detail.
And to answer your specific question, I have been able to shoot over 60 rounds at a session with my R9 before my right hand starts to complain.
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