This weeks "improvements" to my 625.
In order to make the trigger pull as light as possible, I'd screw out the strain screw 1/2 turn and if the gun shot reliably, I'd make a few passes with a small file and try again. When I got to the point where if I loosened it 1/2 turn and it misfired, I'd stop right there. Put Loctite on the screw and tighten it up.
Of course now of days, being so much older an wiser I though I'd measure all my extra screws. The critical part is from the base of the head to the tip. There's no guarantee that all the heads are the same size. And of course going from gun to gun such measurement is meaningless since you don't know the tolerances on the frame, or the depth of the screw's hole, or the exact placement of the main spring. But for working with one gun I know what I need. (See picture.) I used the depth gauge to measure. A very repeatable measurement unlike other ways of measuring.
The strain screw that came with this gun was 10mm long. (yes I've gone metric... for some things) My longest spare screw is 9.4mm and produces misfires. Best I can tell the pitch of the screw is 0.4mm. So half a turn is 0.2mm. Next trip to range I'll take micrometer and files and work it down in 0.1mm increments. Just hoping I don't go too far.
THIS ISN'T THE PROBLEM. It's a pain but it's the sacrifice to have a really slick gun.
Since all my screws are much to short for this gun, I ordered some spares. I assumed they'd be around 10mm. WRONG. They are all 9.36mm. They might be usable in some of the other guns, but totally worthless for this one. Now I've got to find out how I can get the specs from the manufacturers before I order more. At ~$7 a pop I could order one each from the other 3 makers and hope at least one is long enough.