Cylinder Over Rotation

It sounds to me like a weak bolt spring.

tembotusk said:

I have a question about cylinder over rotation. I’ve done a search, but could not find a clear answer.

The pistol is a Pietta 1851 with a 45cal Kirst Konvertor.

I have marked the cylinder and ring for clarity: The first picture shows the cylinder after a slow cocking. The second picture is after cocking faster. The third photo shows the position of the cylinder after harder cocking or faster than the second photo.

If I let my hand drag the cylinder, it will always go into battery.

Question:

1: Is the hand too long?

2: Is there an issue with the bolt?

3: How do I fix the issue?

Thanks for any advise!


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Cylinder over rotation or throw by as it is more commonly called is generally due to the bolt not rising early enough. The bolt should pop up just a bit prior to the lead of the notch if you intend to do a lot of fast cocking as in cowboy shooting. The fact that is goes into battery with slow cocking or friction from dragging your hand indicates everything else is working OK. To correct this you would remove a small amount from the rear of the bolt leg until the bolt rises just prior to the lead in of the notch.

I would check to be sure the bolt is not dragging as well before removing any material. Once you remove any metal it's harder to put it back.

Are you doing the testing with the cylinder empty or loaded? The weight of a loaded cylinder provides more kinetic resistance and that alone might take care of the problem. (For safety's sake use dummy rounds with no powder or primers when doing this testing.)

Is this a problem also with the original percussion cylinder, or only with the Kirst converter?

Piettas often have poor fit between the bolt and cylinder notch. Check the width of the bolt compared to the width of the cylinder notches. It may be that the bolt is too wide for the notches which prevents the bolt from seating and locking down into the notch completely. The solution in that case is to reduce the width of the bolt so that it will fit into the most narrow notch. (Notch width can vary; use a good micrometer to check theses dimensions.)

J-Bar said:

Piettas often have poor fit between the bolt and cylinder notch. Check the width of the bolt compared to the width of the cylinder notches. It may be that the bolt is too wide for the notches which prevents the bolt from seating and locking down into the notch completely. The solution in that case is to reduce the width of the bolt so that it will fit into the most narrow notch. (Notch width can vary; use a good micrometer to check theses dimensions.)

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Bolt width is always a good thing to check and should be about .002 less than notch width or a bit more. However since the gun goes into battery when slow cocked or cocked against resistance that is not likely the problem. It is a timing issue and the bolt is rising late. It should rise and contact the cylinder when slow cocked just at or a bit before the lead into the notch.

J-Bar said:

Piettas often have poor fit between the bolt and cylinder notch. Check the width of the bolt compared to the width of the cylinder notches.

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Remember that we're talking about an aftermarket conversion cylinder here. The discrepancy could be even worse than with the original Pietta cylinder. At least the fit of the original cylinder could have been checked at the factory. With a conversion cylinder, you are on your own.

denster said:

Bolt width is always a good thing to check and should be about .002 less than notch width or a bit more. However since the gun goes into battery when slow cocked or cocked against resistance that is not likely the problem. It is a timing issue and the bolt is rising late. It should rise and contact the cylinder when slow cocked just at or a bit before the lead into the notch.

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A poorly fitting bolt can stop a slowly rotating cylinder even though the bolt is not completely bottomed out. You will probably start to see the edges of the notches getting buggered if it goes on long enough. It’s relatively easy to check bolt-notch fit before replacing springs or hands or removing metal from other parts. There is a good chance that a combination of the issues discussed above are contributing to the problem.

Don't forget the hand spring acts as a brake.

Since the original percussion cylinder works perfectly and the conversion cylinder doesn't, there must be something different about the conversion cylinder that is causing the problem. (Duh!) Compare the locking notches as well as the ratchets.

I had something of a similar problem with a Howell conversion cylinder in an Uberti '58 NMA. I contacted Howell and they told me of the simple solution, which was to file a 45 degree bevel on the tip of the hand -- on the inside surface and no more than half the width of the hand. This cured the over-rotation problem on the conversion cylinder, and had no detrimental effect on the percussion cylinder. (Howell does not provide this information with all their conversion cylinders because, they said, not all guns have this problem and they don't want to confuse the buyers.)

Get yourself a spare hand before trying this, in case it doesn't work. Hands are relatively cheap.

This is not a hand length issue. It is a bolt timing issue. The OP says the bolt is coming up and contacting the cylinder after the notch has passed. With the percussion cylinder in place, which works, I'll bet the bolt goes into the notch and the cylinder stops rotating right at the moment the bolt comes up. This works for the moment but as the parts wear the bolt will start peening the edges of the notch. Trimming the rear of the bolt leg until the bolt rises just at the beginning of the lead will cure the problem for both cylinders.

denster said:

This is not a hand length issue. It is a bolt timing issue.

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If it was a bolt timing issue you would expect that the percussion cylinder would be affected also.

It is much simpler to adjust the hand than to mess with the bolt. Try the simplest solution first. Bolt timing involves a skill that most of us don't have.

It is not so much the length of the hand, but rather the angle of the tip of the hand. It has to match the ratchet of the cylinder, and I would bet that the conversion cylinder has a considerably different ratchet than the percussion cylinder.

AlexanderA said:

If it was a bolt timing issue you would expect that the percussion cylinder would be affected also.

It is much simpler to adjust the hand than to mess with the bolt. Try the simplest solution first. Bolt timing involves a skill that most of us don't have.

It is not so much the length of the hand, but rather the angle of the tip of the hand. It has to match the ratchet of the cylinder, and I would bet that the conversion cylinder has a considerably different ratchet than the percussion cylinder.

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And the percussion cylinder, as I stated, likely is effected. We are talking a very small difference here. The OP states the notches in the percussion cylinder are larger than on the conversion maybe just enough that the bolt manages to drop in. It is real easy to check just look under the cylinder from the right side and watch the point where the bolt rises in relation to the notch. To the OP this is easy to adjust if you look at the leg of the bolt that rides over the hammer cam you will see the very rear of the leg is cut at a vertical angle. Maintaining that angle you file off a few file strokes and check where the bolt now falls. Repeat until it rises just at the lead into the notch. Probably only take two fittings three at most to get it right.