See …. You no-good, so-and-so’s have tricked the poor Old Fuff into revealing one of his deepest secrets. But then it’s well known that he’s pretty easy.
The trick works, but you can save some time if you use a piece of soft rod stock (even a nail if it’s the right size) to make a pattern. The pin should be an easy slip fit inside the spring (spring inside diameter’s can vary) and the final pin should be hard and polished. If one doesn’t have a selection of pin stock (available from Brownells at:
www.brownells.com they can select a twist drill of the right size and cut off the shank.
Start with the pattern-pin and cut it so you can see about 1/8†inch sticking out at the front of the slot in the rebound slide. This should be too long, and the trigger won’t move nearly far enough. But as you SLOWLY AND CAREFULLY trim the pin you’ll get to where you want too be. If you reassemble the lockwork without the hand you can better see what you are doing and what going on. Do have a magnifying glass handy. You will probably end up making several pattern-pins but when one is right, measure the length and you’re set to go in making the real part.
I have on occasion installed a pin to block the hammer’s rearward travel, but this involved drilling a hole in the frame and sideplate, and I decided it was a good case of overkill, being neither necessary nor desirable.
S&W has used a similar method to make a single-action trigger stop in some N-frame revolvers, but it is generally worthless because they don’t (or didn’t) take the time to get the length right.
One side benefit of the rebound slide pin arrangement is that it reduces or eliminates the problem some have of their finger being pinched between the back of the trigger and the trigger guard. Last but not least, no irreversible changes have been made to the gun that you can’t easily undo if you want to.
If one isn't sure about the concept of D.A.O. and a bobbed hammer they can install the pin as described to in effect block the single-action and try it out for awhile. Then and only then go the rest of the way and cut off the hammer spur (or replace the hammer with a bobbed one) if that's what they still want.
I strongly recommend that those who want to do any "homesmithing" or simply service a S&W revolver obtain a copy of Jerry Kuhnhausen's "The S&W Revolver - A Shop Manual," that is also available from Brownells. This book will pay for itself in preventing the mistakes that you don't make.