Python timing peculiarity

[CDH]

Hi guys, first post here.

I have a stainless Python w/6" barrel that acts peculiarly. Let me first say that I went through Jim March's procedures for checking out a revolver, and this Python seemed to pass perfectly. It's serial number is K937**.
In full lockup, there is absolutely no cylinder play front to back or side to side, and the front gap is .004 which feels awful good to me.
With the hammer down and trigger forward, there is just a very slight amount of (expected) rotational cylinder play. No problem there.
Plus, you can pull the hammer back to SA cocked position and it does so as smooth as butter (most of the time, which leads to the following):

So with that mental picture of a "perfect" revolver in mind, here's something I haven't figured out yet:

Looking at the pistol from the rear in it's hammer down, trigger forward condition, it's ready for SA cocking.
And it cocks SA fine most of the time, but occasionally the hammer will hang up and stop about 1/8" into the SA cock.
So I fiddled with it, and finally noticed that this can be reliably forced to happen by gently rotating the cylinder clockwise to where it stops (as seen from the rear) and then trying to SA cock it. Keep in mind that there is only about .015 (guesstimate) of movement in rotation available to the cylinder in any of the 6 cartridge positions in it's unlocked condition.
So when I turn the cylinder clockwise to where the cylinder is against it's stop, the hammer will always hang up 1/8" back into the SA cock and won't go any further.
Then if I gently move the cylinder counter-clockwise just enough to get the cylinder away from it's clockwise stopped condition, it will always SA cock just fine.

My feeling is to just send it off to Colt, but I'd like to know a little more about what's going on with it before I do. On the other hand, someone here might be know about this problem well enough to suggest a simple fix that won't require any smithing.

TIA,
Carter

 

[Old Fuff]

What I think is happening is that the bolt isn't dropping out of the notch in the cylinder soon enough, and as a consequence the cylinder can't turn. That being the case the hammer can't come backwards any further then it does.

Swing the cylinder out, and continue cocking and lowering the hammer. See if it hangs up the same way as it does with the cylinder closed. I not, you have a strong clue about what's going on.

The cause could be as simple as the bolt screw being loose, or some dirt and fouling in the wrong place.

It might be fixed by a good cleaning and fresh lubrication. If not, it would be best to send it back to the factory.

 

[4v50 Gary]

If it needs adjusting, tweaking the bolt tail so it'll drop off faster from the shelf of the rebound lever may help. But like Old Fuff (whom I respect highly recommended already) this is a job I'd leave for the pros.

 

[dfariswheel]

As an aid to checking your Python's timing:

Here's my instructions on how to check Colt timing:

To check Colt timing:

BOLT RETRACTION AND "SNAP BACK".
Open the cylinder and look at the small "lug" in the bottom of the cylinder window. This is the cylinder locking bolt.

Cock the hammer, and watch as the bolt retracts into the frame and pops back out.

The bolt MUST begin to retract THE INSTANT the hammer begins to move.
There MUST be NO (ZERO) hammer movement possible before the bolt starts to retract.

The bolt should retract smoothly with no hesitation until it's fully retracted, then it MUST pop back out with a clean "snap".
There should be no hesitation, and no amount of "creeping" back out.

CYLINDER UNLOCKING.
Close the cylinder.
Use your left thumb or fore finger to again cock the hammer, closely watching the cylinder bolt as you SLOWLY cock the hammer.

As the hammer comes back, the bolt will retract away from the cylinder.

The bolt MUST retract far enough to unlock the cylinder BEFORE the cylinder begins to rotate.

If the bolt is still slightly engaged with the cylinder lock notch, the cylinder will be attempting to turn while still partially locked.

This produces a "catch" or "hard spot" in the trigger pull and will damage both the bolt and the cylinder lock notches.
This often appears as metal "pulled out" of the lock notches, with rounded off and burred notches.

BOLT DROP TIMING.
Continue to cock the hammer, laying your right index finger on the cylinder just enough to prevent "free wheeling".

Watch for the bolt to drop back onto the cylinder. WHERE the bolt drops is CRITICAL.

The bolt MUST drop onto the lead or ramp in front of the actual cylinder notch.
If the bolt drops too soon, (in front of the notch ramp), it will mar the finish of the cylinder.

The bolt SHOULD drop into the MIDDLE 1/3rd section of the ramp.

If the bolt drops late, (farther toward the actual locking notch) the revolver may display "cylinder throw-by".
In this condition, during double action shooting the cylinder may rotate PAST the locking notch, and fire in an unlocked condition.

It's the nature of the Colt action, that a hesitant or jerky trigger pull by the user can induce throw-by in even a properly tuned Colt.
The Colt trigger should be pulled with a smooth, even pull, with no sudden jerks at the beginning.

CYLINDER LOCKUP.
Continue to pull the hammer back and both watch and listen for the bolt to drop into the cylinder lock notch.

The bolt MUST drop into the actual lock notch BEFORE the hammer reaches full cock.

The most common Colt mis-time situation is the hammer cocks before the bolt drops into the lock notch. (Hammer is cocked, but cylinder isn't locked).

In this condition, with the hammer fully cocked, you can push the cylinder slightly, and you will hear the "CLICK" as the bolt drops into lock.

In my experience, most Colt's leave the factory with the bolt dropping a little late into the lead, but usually wear in to correct timing.

If the bolt drops onto the cylinder early, no real problem, but there will be extra finish wear.

If the bolt drops late (closer to the lock notch) the cylinder may "throw by" or rotate TOO far in double action and this can cause off-center primer hits and firing while unlocked.

Each of these checks should be done on EACH chamber. All of these checks are better done individually. In other words, do the bolt retraction check on all six chambers, then do the bolt drop test, and so on.

A properly tuned Colt will:
Have a smoothly functioning bolt with no sticky or hesitant movement.

Unlock before the cylinder begins to turn.

The bolt will drop onto the middle 1/3rd of the ramp.

The bolt will drop into the lock notch before the hammer reaches full cock.

Have a smooth trigger pull, which does "stack".

 

[CDH]

Thanks guys, it appears that you all nailed it. While the cylinder bolt DOES begin dropping immediately as soon as the hammer moves, I can see that it doesn't always drop fast enough or far enough. Additionally, the bolt HAS left a polished line around the cylinder where it rides it which I should have snapped to right away (I didn't, though, because most of my revolvers of all brands seem to pick up that same mark over time).

I'm a lot more mechanically capable than most guys (I won't bore anyone with my credentials here), but it's because I'm "that good" that I understand the big picture of how all the internals work together and have to be perfectly timed in order to work well.

So off to Colt it goes.

Thanks again,
Carter

 

[dfariswheel]

Note that ALL revolvers will develop a line all the way around the cylinder eventually.

S&W, Ruger, and the later Colt's like the Trooper Mark III and King Cobra will immediately develop the line, since the design requires the bolt to ride the cylinder through most of it's rotation.

The older Colt action, like the Python will develop the line simply from closing the cylinder and rotating it to lock it.

So, the presence of a line even on the Python does not necessarily indicate a problem.

 

[Standing Wolf]

Thanks, dfariswheel! I knew a little of that.