As a public service, here's my Colt revolver timing checks.
This is for the older models like the Python, Old Trooper, and Detective Special:
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".
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Next, the later transfer-bar ignition guns like the Trooper Mark III, Lawman, Trooper Mark V, King Cobra, Anaconda, and the SF-VI/DS-II/Magnum Carry.
BOLT RETRACTION AND DROP.
In these guns, the bolt retraction and drop is judged by TRIGGER movement.
The bolt should begin to retract within 1/6 to 1/4 of the triggers total movement and drop after about 2/3 of it's total arc.
This is NOT 1/6 to 1/4 INCHES, it's total trigger movement.
BOLT ACTION.
Open the cylinder and look at the small "lug" in the lower frame window.
This is the cylinder locking bolt.
Slowly cock the hammer and watch the bolt as it retracts.
When the bolt begins to retract, it should move smoothly in, then pop back out with a clean "SNAP".
There should be little or no mushy or hesitant movement.
BOLT DROP.
Close the cylinder and slowly cock the hammer.
Watch the TRIGGER.
The trigger should move between 1/6 and 1/4 of its arc before the bolt begins to retract.
What's critical here is that the bolt MUST be retracted enough to be completely free of the cylinder locking notch BEFORE the cylinder begins to rotate.
BOLT DROP.
Again, the standard for bolt drop is based on TRIGGER movement.
The Bolt should drop after about 2/3 of the trigger's total travel.
What's critical here is, the bolt should remain retracted away from the cylinder while the cylinder rotates past the locking notch, and then drop back onto the cylinder before the trigger gets too close to the end of it's movement.
CYLINDER LOCKING.
Before the hammer is cocked, the bolt MUST drop into the cylinder locking notch, locking the cylinder.
Unlike the older Colt actions, there's a wide range of adjustment allowed, and the bolt DOES NOT drop into the lead to the cylinder locking notch.
Since the bolt rides the cylinder for most of it's rotation, these Colt's will have finish wear almost all the way around the cylinder like S&W's do.
The design of the hand in these revolvers is also more S&W-like, in that LENGTH is NOT a factor, WIDTH is the critical dimension.
For this reason, these revolvers seldom develop "hammer's cocked, but cylinder isn't locked" problems.
Unlike the older Colt's, these guns are designed to have parts replaced, and CANNOT be re-fitted or re-tuned.
If they have a problem, new parts are installed.
Also unlike the old Colt's, parts cannot be altered or even polished much.
The parts are sintered steel with a thin, glass hard coating.
Any attempt to polish, or otherwise alter parts will break through the coating, destroying the part.
These parts are ruined by any heating and bending attempts.
The Colt SF series guns like the DS-II and the Magnum Carry seemed to all have a slightly different bolt action, in which the bolt dropped VERY soon after the cylinder started to rotate.
In the few versions I saw, I was concerned that any seating or wear would develop a condition where the bolt would drop right back into the locking notch, before the cylinder would rotate.
They were THAT close.
As you can see, the timing is MUCH less critical here, and you live with what ya got.
There's little tuning beyond spring kits, an NO re-fitting of worn parts.
So, on the transfer-bar Colt's the bolt should retract before the cylinder begins to rotate.
The bolt should drop back onto the cylinder before the trigger gets too close to the end of it's movement.
The bolt should lock the cylinder before the hammer gets even close to cocked.
The bolt "rides" the cylinder for most of it's rotation.
