1911s are ALL hammer fired, not striker fired, and is SA only. Others, such as the metal framed SIGs and the now-discontinued Smith&Wessons, were generally DA/SA, hammer fired and utilized a firing pin very similar to that of the 1911s. The SIGs were also available with either DA only and (I think, I've never actually handled one) SA only.
DA/SA pistols (or revolvers) are hammer fired. With current technology, striker fired pistols (not revolvers) can be classified as either DA or SA. For example, Glocks are classified as DA. Other striker fired pistols are classified as SA. The distinction hinges upon whether there is additional rearward compression of the striker spring actuated by the trigger pull. Additional striker spring compression = DA classification, minimal additional striker spring compression = SA classification. From a pure technical viewpoint, all SAFE and MECHANICALLY SOUND fire control mechanisms will involve a minuscule compression of a spring due to the requisite slight rearward camming action of a properly set up sear engagement needed to disengage the sear and allow the hammer or striker to release.
Somewhere in there some solid hits have to be made. One cannot miss fast enough to win an armed confrontation.
My own opinion: I'm not certain that combo DA/SA is superior over either a DA only or a SA only. That was the dogma put forth back when DA/SA pistols were entering the marketplace. Firearm safety rules apply even when defending one's own person or home, OR when taking people into custody as a LEO. One should NEVER allow yourself to "outrun your brain" when handling a firearm. To do so is a recipe for tragedy.
