North American Arms 22 Short Revolver.  It's less than a year old and probably has 25 rounds through it, maybe 50.  No failure-to-fires until this past weekend. This time, 5 of 5 rounds did not fire.  Very light primer strike on the extreme outer edge of the primer.

I'm pretty handy with things that are mechanical and made my living that way for a long time.  I figured that there would be an obvious reason but I haven't found any.

This is a very simple revolver.  Hammer strikes the primer directly - no firing pin, no blocking bar.   Hammer shows no wear, no burs, can't feel anything rough or imperfect with my fingernail.

Hammer swings fully forward.  I don't have feeler gauges that are narrow enough to measure the gap but it appears to be zero gap between the hammer and the frame.  A narrow strip of paper can't be pulled out with the hammer forward.

I thought the hammer might have a worn bearing where it rotates but there is absolutely zero play in the hammer.

So, maybe it's the cylinder. But there is no visible wear on the bearing surface at the front of the cylinder or on the frame where the cylinder makes contact.  The cylinder can move front and back with .004" play.  That seems like a small amount.  Any less and I think the cylinder would be difficult to insert but I don't know what the play should be here.

Here's daylight behind the cylinder with the cylinder pushed all the way forward.

You can see the gap is more than .004 but there is almost no play so I think the cylinder is where it's supposed to be. 

I'm stumped.  Anybody have any thoughts on what's happening?  I can ship it out to have it repaired but shipping both ways will cost me half what I paid for this.  I would probably just order a new one instead.

Thanks in advance.

Edited October 22, 20233 yr by maintenanceguy
REASON FOR EDIT: I can't spell or type.

Like you, I have made my living with my hands, I would try different ammo and check the spring that sends the hammer forward, maybe it cracked and you are only getting partial force.

How old is your ammo. Some manufacturers have a 2 year shelf life of 22 ammo 

The ammo is old, maybe decades old.  But I shoot a lot and haven't had any issues with ammo so I think my ammo is good.  The primer strikes are obviously light so I think that's the problem - I just don't know the cause.

Redeye might be onto something.  I'll take the side plate off and see if the hammer spring is good. Maybe something inside will jump out at me while I'm in there.

 

1 hour ago, maintenanceguy said:

The ammo is old, maybe decades old. 

The age of the ammo is less a concern than how it was stored.  Do you have another firearm capable of shooting those shorties?  I doubt it's the ammo.

The hammer spring is suspect but also check cylinder alignment and if the timing is correct.

I finally got around to looking at the pistol to try to figure out what's happening. 

I took all kinds of measurements with feeler gauges and digital calipers.  It looks like the hammer protrudes into the primer far enough to fire the round.

And then I found...

some wear marks on one side of the hammer.  And it looks like the hammer doesn't sit in the middle of the slot it is supposed to sit in the middle of.  I think the hammer is making contact with the frame as it heads toward the primer and is slowed down enough by the impact/side scraping that it loses some speed and hits the primer too lightly.

So I found a flat file small enough to fit in the groove and widened it by .002 or .003" and it shoots fine now.  Can't even tell it was modified.   I'm guessing the hammer pivot pin is a little crooked.