I just received and range tested an Iver Johnson TP22 (DA/SA 22LR autoloader). The gun functioned very well with high-velocity ammunition - and rather poorly with LV stuff - but would only fire about 50% of the time when the hammer was cocked in SA mode. On the DA strokes it worked just fine. I have stripped and cleaned the pistol and did not note any mechanical problems. Does anyone have advice on how I might be able to correct this? TIA!
Iver Johnson DA/SA: Cure for Light SA Hammer strikes?
- Thread starter raghorn
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P95Carry
Moderator Emeritus
I do not know this piece in any detail but two things come to mind.
Sometimes in DA the pin impact is a shade more effective than SA - and so perhaps mainspring is ''tired'' such that replacement (if possible) could help.
Second thing is with some 22's - too much dry fire makes the chamber mouth, which is the ''anvil'' become peened and so slightly dished. A pin striked then over this will have to be heavier, to deform rim enough to provide ignition of the primer compound.
Just initial musings! (post a pic if you have one)
Sometimes in DA the pin impact is a shade more effective than SA - and so perhaps mainspring is ''tired'' such that replacement (if possible) could help.
Second thing is with some 22's - too much dry fire makes the chamber mouth, which is the ''anvil'' become peened and so slightly dished. A pin striked then over this will have to be heavier, to deform rim enough to provide ignition of the primer compound.
Just initial musings! (post a pic if you have one)
Here are a few pics. The firing pin strikes at the 12:00 position. The chamber shows no deformation, although it's difficult to see from the photos. The manual safety physically prevents the hammer from striking the firing pin during dry fire; there also appears to be a secondary safety that blocks the other end of the firing pin from contacting the cartridge rim unless the trigger is depressed.
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P95Carry
Moderator Emeritus
Thx for the pics - indeed hard to see any deformation on chamber mouth.
So hmmmm - if not dry fire damage then I am thinking mainspring, altho it does appear a very substantial spring already. Purely out of interest it'd be useful to try and assess rearmost position of hammer in DA and SA modes - just in case travel is a smidgeon better in DA.
I do get the impression with some semi's that a fast DA accelerates a hammer sufficient to take it back beyond the SA position and so imparts a small extra energy input.
Not that it should matter but the FP - is it round or oblong? - and what do fired cases look like for indent. In fact rechamber an empty and whack it on a fresh rim portion to check that too for depth.
One other minor point also - wondering if a round goes 100% into battery - depending on ammo type, feed vigorousness etc. A minute lack of full battery will soak up some pin energy.
So hmmmm - if not dry fire damage then I am thinking mainspring, altho it does appear a very substantial spring already. Purely out of interest it'd be useful to try and assess rearmost position of hammer in DA and SA modes - just in case travel is a smidgeon better in DA.
I do get the impression with some semi's that a fast DA accelerates a hammer sufficient to take it back beyond the SA position and so imparts a small extra energy input.
Not that it should matter but the FP - is it round or oblong? - and what do fired cases look like for indent. In fact rechamber an empty and whack it on a fresh rim portion to check that too for depth.
One other minor point also - wondering if a round goes 100% into battery - depending on ammo type, feed vigorousness etc. A minute lack of full battery will soak up some pin energy.
Thanks for the advice, P95C. The Hi-velocity ammo seemed to cycle well and return fully to battery. The LV stuff (American Eagle 38 gr HP and 40 gr RN) wouldn't even retract the slide far enough to pull the fired case clear of the chamber. The indents in the fired cases aren't as deep as the ones from my Ruger Mk III. Looks like I'll have to do some more research once the range dries up.
P95Carry
Moderator Emeritus
Indents do sound marginal - and if HV ammo all that will work then maybe that is what it will have to be fed.
Quite a few semi's seem bothered by soft ammo. I am making an assumption too that slide is well free. Make sure only lube is something like Militeck1 - any grease could prejudice slide freedom IMO. It did on my SIG when it got cruddy.
Quite a few semi's seem bothered by soft ammo. I am making an assumption too that slide is well free. Make sure only lube is something like Militeck1 - any grease could prejudice slide freedom IMO. It did on my SIG when it got cruddy.
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