jambie wrote:My MarkIII is experiencing an abnormal number of FtFs
I have changed the firing pin but that did not help.
Looking at the spent shells, the show very light firing pin strikes.
I now suspect that the hammer spring or hammer spring plunger may be damaged.
I have not attempted to take the spring or plunger out for examination.
... from your description, your FtF is 'Fail to Fire', right? (not Fail-to-Feed)
Which model(mk3 -or- 22/45), barrel?
How many is Abnormal?
What brand(s) of ammo?
How long have you had the pistol(time/shots)? Did it usta-work, now failing?
Did you get it at a GunShop, with a GunSmith that might be able to help?
Do you have other MKs (to compare to)?
Does the Hammer-Strut appear to be rubbed, such that it might be
mis-aligned/forced down into the mainspring-housing... ?
(can you compare to another for burrs or indications?)
(I don't think you want to consider opening the MainSpring,
just press down with a small pin-punch to get a "feel") is it lubed?
Could anything (crud?) be holding the bolt-face back from the chamber?
that could increase the HeadSpace and result in Strike-Lites.
Does your firingPin easily run Fwd/back in its groove?
Is it clean underneath it, is the little underneath return-spring/guide
aligned/seated properly?
Does a cartridge easily "drop-in" and "fall-out" of the chamber?
indicating no restriction to an easy/full chambering?
Check the ScopeRail-screws that they do NOT penetrate into the receiver
and drag on the Bolt. (or the filler-screws, if no rail used).
This should be enough "first aid", there will be other ideas coming soon.