Full Lock Up Zero Rotation Play

[scruffy]

Background: Chasing down what could have caused a new 629 to shave some copper/lead while firing the first 75 rounds. Never had a revolver do it to that extent before. Every dimension, measurement and test I could take all came out perfectly. Timing, carry up, B/C gap, head space, cylinder throat ID, FC "mouth" ID, (FC looks rough, but the more I read and compared the more think it's a non issue shooting jacketed factory ammo), zero end play, smooth shiny bore and visually good crown.

The only thing left that is different than any of the 10 other S&W revolvers I own is when checking lock up (cocked, hammer lowered, trigger held back) there is zero rotational cylinder play on four chambers. Two adjacent chambers have a very, very small amount of rotational play in lock up. I believe the pawl is responsible for the tight rotational lock up as the "normal" slight amount of play is present on all chambers when the trigger is released and reset. Star rachets looks great with no peening or deformation and cocking and trigger pull is smooth on all chambers in DA and SA.

Big question. Is this lack of rotational play a good thing or a non-issue? Will it loosen up a little with more rounds downrange?

(I should mention after a thorough scrubbing of the FC there was no discernable shaving of copper in the next 75 rounds.)

 

[Pig Hunter]

If the lock up is slightly off it could cause it. You need a range rod to go down the bore to check for interference . The hand and ratchet interaction control that.

 

[Protocall_Design]

Cycling the action, either in dry fire or live fire will eventually wear the ratchets enough so there's a bit of play in the cylinder lockup. The more immediate fix is to file the left side of the hand nose with a diamond file to get the same result. It will only take a thousandth or 2 to get there.

 

[chief38]

A Range Rod could help determine if all cylinders are lining up correctly. Just because a cylinder locks up tightly doesn't guaranty it is lined up correctly. I'd check that first.

 

[scruffy]

Regarding alignment, I don't have a range rod so I visually inspected it using a flashlight checking each chamber while locked up. Looked good and perfectly concentric to me with nothing occluded. I also checked again using a good clean cartridge case with clean rim inserted into each chamber and shine a bright light down the bore which made it easier for me to see the rim alignment with the barrel and again all looked good. Do I need to invest in a range rod? Brownells is sold out.

 

[StrawHat]

How will a range rod help? To slide down the bore it needs to be bore diameter. The cylinder is, at least, several thousandths larger than that so the bullet fills the rifling grooves.

Kevin

 

[Alk8944]

What you describe is perfectly normal and a desirable situation. As Protocall_Design said normal use will cause wear over time and it will loosen up slightly. As long as the hand, not pawl, isn't binding there is nothing to worry about.


Chief 38's remark about a range rod is wrong! Timing cannot be checked with a range rod for the reason StrawHat said. It is only to check gross mis-alignment and is used at matches for safety reasons.

 

[dfariswheel]

Most all modern DA revolvers are specifically designed NOT to lock tightly at ignition.
They may seem to be locked tightly, but there's enough backlash designed in to allow the necessary movement of the cylinder at ignition.

Most modern revolvers are designed with some built in free movement possible to allow the bullet passing from the chamber into the forcing cone to force the chamber into alignment with the barrel.
The benefit of this is the action requires less hand fitting during building and final timing isn't as critical, resulting is a lower priced gun.
The down side is that the bullet strikes slightly off center of the cone and there's some bullet distortion that can reduce accuracy.

Once the trigger is back, no addition movement can lock the cylinder tighter, because the S&W hand bypasses the ejector ratchet and can't press on it any more.
In short, with most guns like the S&W, when the trigger is pulled the cylinder is started with the end of the hand, but full locking is done by the SIDE of the hand bypassing the ejector ratchet and pressing the cylinder the rest of the way.
Once the hand bypasses it can't press any farther.
Cylinder locking is done by the THICKNESS of the hand.

The older Colt revolvers are the only modern guns that lock up tightly when the trigger is pulled.
This is because where the S&W hand is pressing on the side of the ejector ratchet, the Colt hand is PUSHING the ratchet, and the harder the trigger is pulled, the tighter the cylinder is locked by being forced against the cylinder locking bolt.
In the old Colt's, it's the LENGTH of the hand that causes locking.

The upside to the old Colt "Bank Vault lockup" is since the bullet enters the barrel centered, there's less bullet deformation and resultant better accuracy.
The down side is greatly increased hand fitting needed during manufacture and high cost per gun. This is why the old Colt's were discontinued.

The only revolvers in which holding the trigger back to test cylinder locking are the old Colt's.
So, holding a S&W and most other modern revolver triggers back and testing how tight the cylinder is locked is not a valid test.