The
SERIES II has a firing pin block added. Simply, it is a mechanism by which a "stop" prevents the firing pin from moving forward and striking the cartridge primer
until, in this case, the grip safety is depressed. In a Colt Series 80 pistol, the block is moved out of he way by pulling the trigger back.
The
SERIES I guns did not have a firing pin block - as didn't the Colt 70 Series.
(Also - the Kimber guns were never titled "Series I"; that name just sort of stuck when they came out with the "II" guns.)
I've never fired a Series II gun. You'll find posts all over the place complaining about the design or its execution. From as near as I can tell, some of the first run of guns were very picky about having to have the grip safety depressed "just so" to get the whole system working right to fire the gun. Lately, I've read that both the Tacoma WA PD & the LAPD SWAT have chosen the basic Kimber Custom Classic pistols for issue to their officers. In particular, the Tacoma PD used "over the counter" guns in all their evaluations. There is a Tacoma PD employee over at
The 1911 Forum that posted about the tests. It would seem most of the bugs have been worked out.
For me, I'd rather have the
Series I guns - of which I have 2!
But, I wouldn't let the Series II safety stop me from buying another Kimber, if that is what I wanted.
You might also want to check out the newer Colt, SA, & especally the Dan Wesson guns. There are a lot of nice 1911 pistols to choose from these days! From my personal experience, you won't go wrong with a Kimber.