Taurus cylinder end shake

[castmiester]

I have a Taurus model 66 with .009, with a loaded cylinder. Is that acceptable or does it need shimming ?

[Der Gebirgsjager]

A Taurus M-66 is very much like a S&W M-19. The specs for the S&W K-frames call for a maxim of .006" cylinder gap. However, this isn't always a critical measurement, and a bit more isn't necessarily a problem. If your Taurus doesn't spit lead out of the sides of the gap or excessively lead the forcing cone there isn't a problem. If dissatisfied with it's present condition you can purchase thin washer-like shims from Brownell's that will likely solve your end shake problem. Installation isn't difficult, and if you're a total novice you can learn a lot from Kuhnhausen's S& W Shop Manual.

DG

[castmiester]

I had the yoke apart and cylinder before when I shot it alot... easy. So yeah I can get some shims. No lead spitting out on the face of the cylinder or forcing cone, to speak of. Just considered loss of pressure that be inconsistent maybe to effect accuracy. Although I was shooting .359 and the throats are .358, would throw that off accuracy wise. So what the minimum clearance I need ?

[Der Gebirgsjager]

Like I said, above, .006" is standard for most revolvers of the S&W/Taurus type. Some come from the factory with as little as .003". Most gunsmiths I have known considered .006" as the standard spec. Too little gap and you may find that as your cylinder heats up and expands from repeated firing its face will rub against the rear of the forcing cone, and in some revolvers be almost impossible to turn until it cools down.

DG

[Tatume]

What are your actual measurements? Hold the unloaded cylinder fully forward and measure the gap, then hold it fully to the rear and measure the gap again. Subtract the smaller from the larger. For example, measurements 0.006" and 0.015" would indicate 0.009" end shake.

[castmiester]

What are your actual measurements? Hold the unloaded cylinder fully forward and measure the gap, then hold it fully to the rear and measure the gap again. Subtract the smaller from the larger. For example, measurements 0.006" and 0.015" would indicate 0.009" end shake.

Don't know why I should be concerned about what your saying. The forcing cone/cylinder gap, excess gas escape, is what only should be the concern here.

[Tatume]

Don't know why I should be concerned about what your saying. The forcing cone/cylinder gap, excess gas escape, is what only should be the concern here.

You said your concern was end shake. Now you're saying you aren't concerned about end shake. Barrel / cylinder gap is not the same thing as end shake.

[castmiester]

You shim it and it's taken care of up front, where it counts. Tell me what the concern is in the back ? Moderator, Der Gebirgsjager knew where I was coming from, sorry if I used the wrong terminology.

[shooting on a shoestring]

Castmiester, ummm…..no.
The width of the barrel to cylinder gap is secondary in importance to the amount of end shake.

End shake determines the rotational timing of the cylinder. When the hand (or pawl as some call it) engages the cylinder ratchet teeth to push up on the cylinder to rotate it, the hand also pushes the cylinder forward due to the geometry involved. When the cylinder has excess space to move forward away from the hand the result is the cylinder does not rotate as far. Or said another way, the cylinder timing becomes slow. This can be disguised by quickly cocking the revolver and the fly-wheel effect will allow the cylinder to rotate until it’s stopped by the bolt engaging the cylinder cuppet…..up to a point. I once had a J-frame go out of time so far the firing pin would strike the edge of the primer when fired slowly in double action.

If the end shake is small, say under 0.004” or so, it will not grow perceptibly for a long time. But when it gets on the order of 0.010” it will grow rapidly. The reason is because end shake is the distance the cylinder uses to build momentum to peen the cylinder window larger. It’s exactly like driving a nail by swinging the hammer only 1 inch versus swinging the hammer 1 foot. The longer the distance the hammer or cylinder can build velocity, the harder its impact force and the more it moves what it hits.

When the gun is fired, the cylinder is driven forward by the hammer strike. The expanding gases from the burning powder inflate the brass case against the chamber wall. As the boolit is accelerated forward, the brass case accelerates backward dragging the cylinder with it. This forward/backward movement of the cylinder is fast. But if the movement is only a few thousandths of an inch, the velocity of the cylinder is small when it impacts. But if the cylinder can get a longer run to accelerate, the velocity goes up and the energy of the impact goes up exponentially. The result is the cylinder becomes a very powerful slide hammer and batters the cylinder window larger, which gives the cylinder more room to accelerate and hit harder….until the timing gets bad enough to cause problems.

The amount of barrel to cylinder gap has no effect on precision, or shooting groups. It does reduce the velocity by bleeding off pressure. In a rough estimate, each 0.001” of gap equates to about 1” of barrel for velocity loss.

Shimming the cylinder rearward to arrest its movement will add years of life to the revolver. It will also show how wide the gap has grown. Often velocity loss from a wide gap can either be ignored with no ill effects, or compensated by moving to a larger charge of a slower powder. Or the best thing is shim the cylinder and also set the barrel back and recut the gap.

[smorin2]

Castmiester, ummm…..no.
The width of the barrel to cylinder gap is secondary in importance to the amount of end shake.

End shake determines the rotational timing of the cylinder. When the hand (or pawl as some call it) engages the cylinder ratchet teeth to push up on the cylinder to rotate it, the hand also pushes the cylinder forward due to the geometry involved. When the cylinder has excess space to move forward away from the hand the result is the cylinder does not rotate as far. Or said another way, the cylinder timing becomes slow. This can be disguised by quickly cocking the revolver and the fly-wheel effect will allow the cylinder to rotate until it’s stopped by the bolt engaging the cylinder cuppet…..up to a point. I once had a J-frame go out of time so far the firing pin would strike the edge of the primer when fired slowly in double action.

If the end shake is small, say under 0.004” or so, it will not grow perceptibly for a long time. But when it gets on the order of 0.010” it will grow rapidly. The reason is because end shake is the distance the cylinder uses to build momentum to peen the cylinder window larger. It’s exactly like driving a nail by swinging the hammer only 1 inch versus swinging the hammer 1 foot. The longer the distance the hammer or cylinder can build velocity, the harder its impact force and the more it moves what it hits.

When the gun is fired, the cylinder is driven forward by the hammer strike. The expanding gases from the burning powder inflate the brass case against the chamber wall. As the boolit is accelerated forward, the brass case accelerates backward dragging the cylinder with it. This forward/backward movement of the cylinder is fast. But if the movement is only a few thousandths of an inch, the velocity of the cylinder is small when it impacts. But if the cylinder can get a longer run to accelerate, the velocity goes up and the energy of the impact goes up exponentially. The result is the cylinder becomes a very powerful slide hammer and batters the cylinder window larger, which gives the cylinder more room to accelerate and hit harder….until the timing gets bad enough to cause problems.

The amount of barrel to cylinder gap has no effect on precision, or shooting groups. It does reduce the velocity by bleeding off pressure. In a rough estimate, each 0.001” of gap equates to about 1” of barrel for velocity loss.

Shimming the cylinder rearward to arrest its movement will add years of life to the revolver. It will also show how wide the gap has grown. Often velocity loss from a wide gap can either be ignored with no ill effects, or compensated by moving to a larger charge of a slower powder. Or the best thing is shim the cylinder and also set the barrel back and recut the gap.

Thank you for posting such a well written and easy to understand explanation. I have a Taurus with similar issues.

[castmiester]

Shooting on a shoestring...

When the gun is fired, the cylinder is driven forward by the hammer strike.

Considering above yes, below is true.

The amount of barrel to cylinder gap has no effect on precision, or shooting groups.

Shimming the cylinder rearward to arrest its movement will add years of life to the revolver.

will keep this in mind...

I loaded a snap cap and cocked and released the hammer keeping pressure on the firing pin and felt no cylinder end shake, thanks for this info.

[Tatume]

That's not how you detect or measure end shake. Hold the unloaded cylinder fully forward with one hand and measure the gap with the other hand. Then hold it fully to the rear with one hand and measure the gap again. Subtract the smaller from the larger. For example, measurements 0.006" and 0.015" would indicate 0.009" end shake.

[Electrod47]

Thanks shootingonashoestring.....perfect breakdown of the topic

[castmiester]

That's not how you detect or measure end shake. Hold the unloaded cylinder fully forward with one hand and measure the gap with the other hand. Then hold it fully to the rear with one hand and measure the gap again. Subtract the smaller from the larger. For example, measurements 0.006" and 0.015" would indicate 0.009" end shake.

Shimming the cylinder rearward to arrest its movement will add years of life to the revolver. It will also show how wide the gap has grown.

Is the main thing… watch how much it increases by the end shake decreased by locking the firing pin pushing the cylinder forward. Once it worsens increasing is when you shim it. The shims are inserted between the yoke and cylinder bushing which is up front.

[castmiester]

update

I noticed I have a cocked cylinder when looking at the gap between the forcing cone and cylinder, gap is on a slight angle, yes.. The bluing on the yoke is slightly wore off but mics evenly all the way around on both shoulders on the shaft that engages the collet inside the cylinder. Thinking a bad collet (retainer bushing) ? I would say that would effect accuracy.

[jrayborn]

I want say that if you don't understand even the basic nomenclature and mechanical workings of something, you may want to seek the help of someone who does.

I understand that some might be insulted by this, however there is a safety element here. I just want to point out that we all have limits of knowledge or ability, and there are times that it doesn't REALLY matter. In the case of firearm repair or even just disassembly/assembly it most certainly does. Please be careful folks.

[FergusonTO35]

Working in a busy shop, I will say the barrel/cylinder gap of modern wheelguns seems to be alot more consistent than it used to be. Even cheapies like the Armscor revolvers are pretty consistent, .004-.006. A yawning b/c gap irritates the crud out of me, even if the gun shoots well.