Unlike the old 1911 type thumb safety, which does not allow the slide to be moved with the safety on...my HK45 allows me to:
-rack the slide and chamber a round with the safety on for Condition One mode
-rack the slide with the safety on and with the hammer cocked to clear the pistol
-engage the safety first and and then cock the hammer for Condition One carry
-engage the safety with the hammer down to prevent any firing of the pistol
-and of course, use the safety lever to de-cock the pistol
-use the thumb to slow the hammer drop (much quieter) while de-cocking the pistol
In checking, I notice that the firing pin block seems to remain engaged under these conditions, until just after the trigger is pulled far enough to break the sear to allow the hammer to fall.
My round-about question is: am I OK to operate the pistol's safety lever in all these positions without harming the fire control group?