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Old 09-06-2020, 12:57 PM
Green Frog Green Frog is offline
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Default Retro Fit Decockers

OK, I know it is possible to use a Gen 3 ambi decocker safety on a Gen 1 or 2 slide because I’ve seen it done, but should a Gen 2 D/S (from a 639 in this case) work on a Model 915 (ie. Gen 3) slide? Mine went on OK but has to be “encouraged strongly” to go onto safe. It comes back to fire position with only slightly greater than normal effort. Is this just a result of tolerance stacking or is it a larger concern?

Froggie
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Old 09-06-2020, 03:25 PM
JohnHL JohnHL is offline
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Originally Posted by Green Frog View Post
OK, I know it is possible to use a Gen 3 ambi decocker safety on a Gen 1 or 2 slide because I’ve seen it done, but should a Gen 2 D/S (from a 639 in this case) work on a Model 915 (ie. Gen 3) slide? Mine went on OK but has to be “encouraged strongly” to go onto safe. It comes back to fire position with only slightly greater than normal effort. Is this just a result of tolerance stacking or is it a larger concern?

Froggie
Most likely "tolerance stacking", but that is a somewhat ambiguous term.

If the safety lever is difficult to engage with the slide OFF the pistol, it is one part causing the problem.

If the safety lever is difficult to engage with the slide ON the pistol, it is a different part causing the problem.

When the slide is off the pistol, the only thing that should be impeding movement is the interaction between the manual safety detent plunger and the slide detents.

Remove the slide and remove the plunger and spring from the left side of the safety body.

Re-insert the safety body in the slide and move it.

If it moves with no difficulty, the problem is a rough plunger dragging in the slide.

Try the plunger and spring from the 915 slide and see if that improves it.

If the difficulty only occurs with the slide installed on the pistol, the only thing that could be causing the problem is the interaction between the safety body and the sear release lever.

When the safety is engaged with the slide installed, the safety body must depress the sear release lever (middle frame lever of the three) to drop the hammer.

That difficulty could be caused by a roughness on the safety body where it drags on the sear release lever OR the contour of the safety body (or the location of the safety bore in the slide) could be enough to push the sear release lever FARTHER into the frame, against the resistance of the sear and spring (the "tolerance stacking" you mentioned).

The fix for that would be to fit a new sear release lever which would work with the new 3rd gen slide/2nd gen safety body, but might not always decock with other combinations.

Anytime parts are swapped, decock timing should be checked.

That is to say, when the safety is engaged, the safety body must block the firing pin BEFORE the hammer drops.

There are a couple of ways to check decock timing, but a quick and easy "field test" is to place an unsharpened pencil, eraser first, into the barrel of the UNLOADED pistol, point it skyward, and engage the safety.

The hammer should drop and the pencil should NOT move.

Try it several times.

If the pencil moves, the hammer is striking the firing pin BEFORE the the safety body blocks it, and that is no bueno, as they say in the southwest.

John
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Old 09-07-2020, 10:01 AM
Green Frog Green Frog is offline
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Thanks, John. That is what I needed to know. If I push down slightly on the slide while pushing the right side lever, I can get it to decock. OTOH, no amount of pushing or pulling of the lever on the left side makes the decock function work. I’m guessing I’ve got a mismatch between the sear release lever and the shaft of the decocker, generated by a slight difference in the 439 slide machining (with which these parts all worked) and the 915 slide (where the problem arose.) In fact, when I tried assembling the gun with the complete 915 slide and single side safety, the decock lever wouldn’t turn far enough to work at all. I’m now guessing the hole for the decocker in the 915 slide is enough lower to take away all the slack so that lever can move (hence my use of the term “tolerance stacking”) and may be overcome by changing the sear release lever in the frame, but then my other slides may not function properly on that frame. ;eek: “Oh what tangled webs we weave...“

But then again, the total package looks so good with the matte blue 915 slide on the stainless 639 frame, I really want it to work!! I’ve got a deal working for a stainless ambi Gen 3 decocker, so maybe I’ll just wait and see if putting that part in will change the “stack” enough to let everything work again.

Froggie
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