Failure to fire

[sgtt]

I did a trigger job on a handi. Periodically it now fails to fire when the hammer extension is installed.  Take it off and it works all the time.  Thoughts?  Did I reassemble incorrectly?

[quickdtoo]

Weak hammer springs are the most likely cause, I replace the spring with a Wolff heavy spring whenever I do a trigger job, mounting the extension lower on the hammer helps too. Light trigger pull weights commonly cause FTF due to the transfer bar not staying up, make sure you pull the trigger all the way to the rear and see if it helps. See the FAQs for more info.

Tim

[tacklebury]

Yep, the extra mass of your hammer extension is probably slowing the fall speed slightly.  Sometimes it doesn't take too much weight to mess things up.