Warning Signs
There are a few, romulus,
Hammer follow to half-cock during a slidelock reload is a big one. A
very light trigger pull after a slidelock reload is another one. It can
be tested periodically by loading one round into a magazine and
letting the slide slam it into battery using the slidestop to release it.
I keep dummy rounds for things like this...A snap cap will work too.
The dynamics of the event is thus:
The slide slams into battery and the pistol is jerked forward. The trigger
obeys Newton's dictum that it must remain at rest, and the sear, which is
moving forard with the gun, gets nudged a little. Simply put, it's like the old hunting horror story of a twig getting into the rifle's trigger guard while the hunter is walking. Bang.
The hammer is also affected when the slide slams home. Its own inertial
mass causes it to try to move slightly farther back from full cock. If the
mainspring isn't up to the task of getting it back onto the sear before the
sear can rotate, the hammer falls. It usually catches on the half-cock,
but sometimes not. If you get a hammer followdown, don't load the gun again until you fix it.
Since it's caused by inertia, more weight in the hammer and trigger makes
it more likely. Lightening either of these makes it less likely, along with making the sear lighter will make THAT part respond faster to any tension
from the sear spring. My two newest Colts...an XSE Commander and a NRM Gov't Model, both had lightened sears, so it appears that the trend is
toward little things that counter the effects of inertia...at least from Colt.
Generally speaking, hammer hooks that are close to the original design specs are long enough to catch the sear before a followdown can occur,
even with springs that are at a less than optimal tension level. JMB put
long hammer hooks and a 23# mainspring in the pistol for a very good reason...Best not to tinker with'em overmuch.
Happy New Year all!
Tuner