Weird .22 firing problem...

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jwfilion

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I was asked to take a look at a friends Cooey 600 that he inherited. He encountered some misfiring when he tried it out. Thought it was really old ammo, as only one of every 5 or 6 fired. I had a spare bolt, so I fitted it nicely to the gun. Still misfires. The chamber face looks as good as the model 60 I have, and mine shoots well. There are no burrs getting in the way of the firing pin. I tested the bolt face with machinists bluing and the bolt face is making contact with the chamber face. Can't get my head around it.
Then...while testing it this morning, I discovered that if I put forward pressure with my thumb on the bolt handle base and pull the trigger, every shell will fire! No pressure, no firing! If the fit is that close, how can a little pressure on the bolt make that much of a difference? Can anyone give me an idea as to what is going on?
 
Many bolt-.22's (Savage MkII's, for example) use the rear face of the base of the bolt handle, where it slots down into a groove on the receiver, for their primary headspacing. Building up either a) the rear of this portion of the base of the bolt handle, or b) the matching face of the receiver groove it fits into, will likely fix the problem.

The cam effect of the bolt closing completely has a huge effect on heaspacing. The tiniest bit of slack will cause the symptoms you describe.
 
Thanks for your reply. I understand where you're coming from, however when I fitted the bolt, I tried for no play at all. Afterwards, when I tried to figure this out, I found that the face of the bolt and the chamber face, make contact. Obviously, when I used the go gauge to fit the bolt, I was actually making contact with the chamber face and not the gauge. The bolt cannot go forward any more. Would it be possible to remove a small amount from the chamber face? This would move the bolt forward, bring the bolt closer to the shell and provide enough room for a shim if necessary? Just a thought. I'm always open to suggestions.
 
That might help, but it would exacerbate the gap at the rear of the base of the bolt handle by allowing the bolt to move forward a few .0001"s. As you say that putting forward pressure on the bolt handle alleviates the problem, it seems that the bolt must have a tiny bit of forward play.

On thinking about this further, I did a little research, and it appears that this is not uncommon in the 600. However, the problem is usually not at the bolt, but rather at the screw that holds the stock onto the barreled action & the female stud that this bolt screws into. From what I can tell, if either of these is a bit loose, it allows a misalignment of the tube magazine, preventing proper headspacing...or something like that.

I found an old post on the Alberta Outdoorsmen forum dealing with this issue (see post #2 here - http://www.outdoorsmenforum.ca/showthread.php?t=10640 ).

I did find the odd Youtube video about disassembling the 600, which touches on this issue as well (http://www.youtube.com/watch?v=bZf-YHdn04o )

Hope this helps! Keep us posted - from what I'm reading, this is a fairly common problem. Worn firing pins are also a source of this issue...
 
Jeezzzzz...I thought this was going to be a simple solution, but now I'm not so sure. I can't see how the assembly screw being loose can affect the head spacing. I will consider this in my search for answers.
 
Well, if I understand it correctly, the tube magazine & follower can move backward if the screws aren't tight, pushing back on the bolt enough to make ignition inconsistent. Of course, I don't own one, but considering this problem has been reported numerous times, I suspect it's worth looking into.
 
What sort of print do you get from the firing pin on the case when this happens? A light strike I suspect. If all else fits properly, then perhaps a replacement firing pin that is 0.010" or 0.020" longer would do the trick for that particular rifle. I'm sure that this would be easily made by any gunsmith (or may even already exist)
 
There is barely any mark on the shells as you suspected. I can make the pins myself. I've been a machinist for longer then I care to admit. I just need to drill out the keeper pin and see what the firing pin looks like. Will keep you informed...
 
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