Here's the measurement method and the specs:
With the gun UN-COCKED and the action at rest gently push the cylinder forward and hold it there.
Use an automotive feeler gage to gage the barrel/cylinder gap.
Push the cylinder to the rear and hold it while you gage it again.
Subtract one measurement from the other and that's how much cylinder end shake you have.
For S&W revolvers, the end shake cannot be over 0.006".
Colt's are much tighter specs with the maximum allowed being 0.003".
S&W revolvers can have end shake corrected by three methods.
1. Trim the rear of the cylinder yoke to true it up, then install greased hardened stainless bearings.
2. Stretch the yoke barrel by inserting a hardened steel stud to act as a support, then gently peen the yoke barrel to stretch it.
3. Use a special tool made from a tubing cutter to stretch the yoke barrel.
The tubing cutter has the hardened cutting wheel rounded off to a round, non-cutting edge.
The tool is used on the rear of the yoke barrel. Instead of cutting a groove, the tool rolls a round groove in the barrel, stretching it.
Colt's are VERY different.
You CANNOT use washers or crane barrel stretching on the Colt's since the Colt system is totally different than the S&W.
To correct Colt end shake, the gun must be sent in to the factory, or to one of the VERY few people in the world who have a special hydraulic cylinder collar stretching device.
This device is a pair of hydraulically operated "pincher fingers". A hardened steel stud is inserted into the cylinder to support the collar.
The pincher's fingers are used to grip and squeeze the collar on the front of the cylinder. After squeezing, the cylinder is rotated slightly and squeezed again, until there's a reduced area around the collar.
This actually stretches the collar slightly.
This can be done to the cylinder ONE and ONLY one time due to work hardening of the collar. If the gun again develops end shake, the cylinder has to be replaced, or in the case of guns where no cylinder is available, the cylinder can be carefully machined out and a hardened steel bushing can be pressed in.
Normal barrel/cylinder gap is judged by pushing the cylinder to the rear and gaging with feeler gages. The measurement with the cylinder to the rear is the REAL barrel/cylinder gap, the measurement with the cylinder forward is a false reading caused by excessive end shake.
Normal barrel/cylinder gap is ideal at 0.005"
Colt is out of spec at a maximum of 0.008"
S&W is in factory spec at as much as 0.010".
As you can see, Colt specs are tighter than S&W specs, and this is one reason the Colt's were more expensive, and consistently more accurate.
As for inspecting revolvers with the trigger pulled, this is a valid test ONLY for Colt revolvers, and ONLY for checking the Colt cylinder lock-up.
This is NOT a valid test for S&W, Ruger, Taurus, or Dan Wesson.
All of those revolvers are specifically designed to allow the cylinder to be slightly loose with the trigger held back, and this is so the bullet passing from the chamber to the bore will force the cylinder into alignment with the bore.
Measuring barrel/cylinder gap, or end shake with the trigger held back will give false readings.
