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Old 05-02-2018, 12:24 PM
blueticker blueticker is offline
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Default Model 648 misfire problem

My Model 648 (22 MRF) is not striking the primer hard enough & misfiring. I get about a .004" dent, & am told it needs to be .012". Anyone else with this problem or know of a solution?

Thanks, blueticker
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Old 05-02-2018, 01:02 PM
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First thing - make sure that the strain screw is all the way in. This is the screw at the bottom of the front of the grip frame (where your pink lands most times).

Good luck!
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Old 05-02-2018, 01:21 PM
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Are the hammer, springs, screws and trigger S&W factory stock or have you been monkeying with them ....Apex trigger kits , Wollf replacement springs and such....be honest , what all did you do ???
Gary
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Old 05-03-2018, 12:18 PM
blueticker blueticker is offline
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Default 648 misfires

Nothing has been altered, had gun 20+ years, just started to misfire last fall, no idea what the problem could be, some brands of ammo (CCI especially) are worse than others, Aguila has least misfires, but still does about 20% of time
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Old 05-03-2018, 12:30 PM
Jamesatrange Jamesatrange is offline
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If nothing has been changed, my vote is to check the strain screw as SAfireman stated.
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Old 05-03-2018, 01:21 PM
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As suggested - tighten the strain screw. Rimfires are not as sensitive as centerfiresvand need a good smack to the rim.
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Old 05-03-2018, 03:27 PM
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Default Model 648 misfiring

My gunsmith said the strain screw was tight, but that the firing pin was too short. He ordered one from S&W & got an even shorter one back, says he has reordered & was told the next one will be long enough. Also said S&W was not surprised by the misfire issue. I have heard of Model 617's with same issue. Anyone else have an relevant info?

Thanks,
blueticker
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Old 05-03-2018, 03:40 PM
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The S&W firing pins seem to vary quite a bit in terms of length....usually between .488" and .495". Apex and Cylinder and Slide both sell slightly longer ones, which are supposed to cure of the issues (misfires) attributed to the shorter OEM f. pins.

A couple of other well known things that can cause problems in the rimfires.....the cylinder assemblies and breechface must be kept as clean as possible, and the headspace should be checked to make sure it is correct. On the rimfires, the rear gauge (headspace) should be .008"-.010". (.008" is better)
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Old 05-04-2018, 10:45 AM
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Another possibility might be a build up of carbon in the chamber making inserting a live round more difficult. This results in some rounds being not fully seated and the hit from the firing pin moving the round forward, so the hit to the rim is softened by the movement.
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Old 05-05-2018, 10:22 PM
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Or there's crud in the bottom of the firing pin well that is now stopping the pin from goin fill travel. Remember after a while old gun oil will harder and make a "layer" that will jack with function at times
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Old 05-07-2018, 12:34 PM
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Not a 648, but I had to change the firing pin on my model 63. Same problem, had misfires. The new (longer) firing pin corrected the problem.
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Old 05-14-2018, 04:51 PM
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Default Model 648 misfiring

Thanks to all above for your insights, surely one or more of these suggestions will solve the problem. blue
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Old 05-14-2018, 04:52 PM
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Thanks to all for your help, blue
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Old 05-14-2018, 05:00 PM
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Maybe swap mainsprings with another and see if that fixes it. That's how I weeded out two used up mainsprings.
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Old 05-16-2018, 02:14 PM
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I would also recommend a new Wolff mainspring, in my experience they make for much better rimfire ignition than the stock spring.
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