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The Walther P22 was one of two ] used in the 2007 ],<ref name="Williams">{{cite web |first1=Reed |last1=Williams |first2=Shawna |last2=Morrison |title=Police: No motive found |url=http://www.roanoke.com/vtshootingaccounts/wb/114655 |archive-url=https://archive.today/20120207181056/http://www.roanoke.com/vtshootingaccounts/wb/114655 |url-status=dead |archive-date=February 7, 2012 |work=The Roanoke Times |date=April 26, 2007}}</ref> with the other being a ]. The P22 was also the selected weapon used in the 2008 ].<ref>{{cite web |date=2008-09-23 |title=Keskustelupalstoilla arvaillaan jo Kauhajoen ampujaa |url=https://www.iltalehti.fi/kauhajoentragedia/a/200809238313265 |access-date=January 16, 2009 |publisher=Iltalehti.fi |language=fi}}</ref>
The P22 may be fired double action at about 11 pounds-force (49 N), and operates as a single action with slightly more than 4 pounds-force (18 N). The P22 operates by blowback energy from the motion of the cartridge case as it is pushed to the rear by expanding gas created by the ignition of the propellant charge. The action will not open until the projectile has left the barrel and the pressures have dropped to safe levels. The gun will not cycle efficiently unless high velocity .22 (5.59 mm) rounds are used.
Chinn, George M. (1955). The Machine Gun, Volume IV: Design Analysis of Automatic Firing Mechanisms and Related Components. Washington, D.C.: Bureau of Ordnance, Department of the Navy.
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