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Ok so I know it’s outlawed to work on by gunsmiths so I’m stuck doing it myself, it’s a old Herbert shmidt 38s I’ve replaced multiple parts tryin to get this thing to work properly crane cylinder internal springs crane hand and cylinder stop this thing was absolutely destroyed when I got it I basically got it finished and back to life one issue, I have the revolver perfectly in time however I will fire and it shoots maybe 2 rounds out of 6 and I know what y’all are about to say it’s a cheap gun blah blah get a new one heard it all but I basically built it from nothing and want to finish it as a challenge but I’m stuck the centerfire rounds all have a nice divot dead center from the pin but they will not all fire there sig rounds not reloads any estranged advice will help to figure out what I need to replace will be greatly appreciated.
 

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It's pretty difficult to diagnose these things without seeing the gun.
However, if the primer is being struck well centered but the round isn't firing, here's some possibilities......

Try a different brand/type of ammo. Not all guns "like" all ammo. Don't ignore this one, it often happens.

Weak mainspring...replace or re-tention if possible......if the gun is a double action and it fires reliably in single action but misfired in double action, it's usually the spring.

Firing pin worn, bent, or otherwise too short...... Replace the firing pin, BUT make sure it's not too long or you get pierced primers...not good. Minus a factory spec for firing pin protrusion you have to play it by ear.

Stretched frame causing excess head space......no repair possible.

Is there a firing pin bushing in the frame, is it loose?...Replace the bushing...Not easy without some serious tooling.

Ejector seat impact damage of the frame. This is when the ejector impacts the breech face and impact indents it leaving an impression of the ejector. Caused by hot loads or a cheap/antique gun that just wears.
Higher quality gun.....machine breech face and fit a factory-new ejector......cheap or old gun.....no repair possible.

Excess cylinder end shake (forward and back movement of the closed cylinder). If you have excess end shake the cylinder is being pushed forward and dissipating the hammer strike.
To measure end shake.....
Get an automotive feeler gauge set at any auto store or hardware store.
Push the closed cylinder to the rear and hold it there, as you use the feeler set to measure the gap between the barrel and front of the cylinder....This is also the actual barrel/cylinder gap which should be from 0.004" to 0.008" but can go to 0.012".
Then push the cylinder forward and hold it there as you gauge the gap again.
Subtract one measurement from the other and that's how much end shake you have.
How much is too much varies from maker to maker. Colt was the tightest spec at a maximum allowed of 0.003".
Other brands can be more, but once you start getting too much end shake, you get misfires as the cylinder moves forward as the firing pin hits the primer.

How to correct this totally depends on the brand of gun.
Colt's require a special hydraulic machine to stretch the cylinder collar. Single actions may have a separate cylinder bushing that can be replaced or have a precision washer put on the base pin.
Brands like S&W and Ruger can be repaired by dropping precision washers into the disassembled cylinder.
Antique guns, usually no repair is possible.
 
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