Mod 18-4 Misfires

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ggross

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I have an 18-4, 1981 vintage, that will misfire at the range. It is not the same cylinder each time. It happens in single or double action. Ammo is CCI Mini Mag Target. I've cleaned and brushed meticulously. Should I be thinking about replacing the firing pin with the Extended Length version? Any thoughts?
 

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Did you check to make sure the strain screw (the one on the grip facing forward) is tight?
 
How many times does it happen in say, every 100 rounds. As good as CCI, it still has some duds.
 
I kept track last time out and in 10 loads (60 rounds) there would be 7 or 8 misfires.
 
When you pulled those rounds did you notice shallower hits than the rounds that fired or was it hard to tell the difference?
 
Have you checked the misfired cartridge cases? Are they indented exactly like the ones that have been fired?

How about replacing the Mainspring?
 
Is ammo hard to fully seat in the chambers? Is their some "drag" when you cycle the action when loaded?

These guns are known for tight chambers, and if a round is not fully set in the chamber, it can cushion the firing pin blow, causing misfires, and sometimes drag the cartridge rim on the recoil shield, causing the action to feel sticky.

I guess it could be endshake as well, causing a head space issue, but I don't know how common that is in rimfires.

I assume the firing pin tip is undamaged?

Larry
 
After loading I rotate the cylinder and run a finger over the rounds and they are all seated the same.
 
Thanks for that. I'll do that on Tuesday when I'm at the range. I'm hoping it's the ammo.
 
Was the gun working normally, then starting having misfires?
Or did you buy it recently and discovered the problem?

A lot of guns that old have had the tip of the strain screw filed down or the screw replaced with shorter or the hammer spring modified or replaced with lighter. Those tricks will give a lighter trigger pull but also a lighter hit on the cartridge.
 
I might pick up a 50 round box of another brand of .22 before going to the range, and try them. CCI are usually good to go, but who is to say you might not have a bad batch.

Larry
 
What does the trigger feel like? Has the action been "Tuned"? Possibly an action job that went too far? But, those primer hits look like they should set off any rimfire ammo. If these were Remington I might understand the misfires, CCI is normally very reliable.
 
Try some other ammo and also check that strain screw to see if it has been filed down to make the trigger feel lighter. Also check the edges of the main spring to see if it's been filed down. Both of these things are sometimes done to lighten the trigger pull.
Personally I think it is the ammo.
 
I'd love to do that Larry but here in Calif. I currently can't buy ammo except when buying a gun, or at a range.
 
When I have had ignition problems with S&W .22s problem is solved by going with a Wolff mainspring (also make sure the strain screw has not been modified). The Wolff springs are IMHO a better design for rimfire.
 
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