I'd offer that while some folks enjoy engaging in a bit of kitchen-table gunsmithing, that carry up/'timing' issues are really more in the realm of what ought to be handled by someone who has some knowledge and experience in diagnosing and correcting them, which usually means seeking the services of a gunsmith or the factory (unless you know a local S&W trained armorer).
Also, checking carry up in a new model S&W revolver (meaning the models which use the new extractor design which isn't held in position by pins mounted to the cylinder under it) requires the use of properly sized DUMMY rounds in the charge holes. The new style extractor is held in position by the cases of the ammunition loaded in the charge holes during live fire (and dummy rounds during bench checks), instead of being held in place by the pins in the old model revolver cylinders. You're not going to be able to accurately check the carry up in a new model S&W revolver without using dummy rounds.
FWIW, the recommended correction in the armorer's manual for a properly diagnosed carry up problem is to replace the hand with a new one (larger).
That may create a 'long ratchet' condition, though. (Think of one, or more, of the extractor ratchets trying to occupy the same space as the hand at the same time.) If so, the specific ratchet(s) will have to be corrected (filed). This requires judicious and proper filing, and unless someone knows what they're doing it's a fairly easy way to ruin a ratchet (and therefore the extractor).
If the larger hand doesn't correct the carry up issue then it's recommended the extractor be replaced, which involves cutting a new one. S&W makes their cutting tools by welding an arm (lever) to the appropriate model trigger and using a hardened cutting hand. The cutting tools are included in armorer revolver tool kits or can be ordered separately.
On a related note, cutting the ratchets on a new extractor requires dummy rounds loaded into the charge holes to position the ratchets (and hold them) for cutting as they will be positioned when engaging the hand during actual firing, or else the extractor's ratchets may not be cut right.
Oversize hands can be ordered from the factory. I ordered a couple of them to try and tighten up a J-frame's carry up once. I can't remember the sizes when they were gauged but there was at least a couple of thousandths difference among each of the separate hands once I had them in front of me on the bench.
In my case the next size up still didn't provide what I felt was acceptable carry up on all the charge holes, and the next one up from that one was too big to easily move within the window. Not wanting to adjust the frame window I cut a new extractor (which requires the use of the cutting arm) and it corrected the carry up when using the new extractor with the original standard hand. I also paid attention in the armorer class when it was recommended that the least expensive part be filed or adjusted.
Checking carry up in a DAO revolver involves slowly pulling the trigger to the rear so the cylinder stop engages the stop notch in the cylinder. (This doesn’t mean pulling the trigger sloooooowwly, though, nor does it involve touching the cylinder to ‘create drag’.) The cylinder stop should engage the cylinder stop notch before the hammer falls in DA (and before full cock in guns with SA capability).
If you believe your 640 doesn’t exhibit normal carry up why not ask the opinion of a gunsmith or call the factory and ask for their advice?
I've been told by at least a couple of factory folks that the newer model revolvers often exhibit carry up where the cylinder stop engages the stop notch in the cylinder just barely before the hammer falls, and that it's considered within spec even if it's very close, as long as the cylinder stop/stop notch engagement occurs before the hammer actually falls.
I’m neither a licensed gunsmith nor a factory technician, but only an armorer, and obviously I can’t know what’s happening with your particular revolver since I’m not examining it. I’m just offering this info for the sake of discussion.
PURDY!!!! Can't wait to crack the frame in that one!!!
sweet, I have one I put a tyler grip on it helps with my large hands , this will be past down in family but never sold
I'm done for a while, first sign of a wheel gun addictI'm done for a while, I need to buy a rifle and glass now.
Enter your email address to join: