S&W revolvers have a lockwork that is VERY easy to work on and "tune". In addition the single action trigger on a typical S&W revolver is nothing short of superb.
I've actually measured the sear creep in single action on several of my S&W revolvers and it ranges between 0.015 inch and 0.017 inch. That's an amount of movement that is undetectable to "feel" for most of us, you have to resort to some pretty accurate measuring equipment to actually find that there is some level of creep in the single action trigger. Basically, in single action the typical S&W trigger breaks like the proverbial glass rod.
As for weight, almost every S&W that I purchased new had a SA break right at 4 lbs. While it's just a bit heavy for precision shooting, it's not an impediment to getting good results.
In terms of the SA trigger, the rebound spring has the greatest influence on the pull weight. I've done a bit of experimenting with a rebound spring kit from Brownells with weights ranging between 11 and 15 lbs. Note, the factory rebound spring has been widely reported as being a 16 lbs. spring. What I have found is the a 12 lbs. rebound spring will yield a SA pull of a bit under 2 lbs. Go to a 13 lbs. rebound spring and the SA pull will break at 2.5 lbs. Next up is the 14 lbs. rebound spring that yields a break just a tick over 3 lbs. I haven't tried a 11 or 15 lbs. rebound spring but the trend I observed indicates that the 11 lbs. spring will produce a SA break around 1.4 lbs. and the 15 lbs. spring will yield a 3.5 lbs. break. Personally, I prefer a SA trigger that breaks at 3 lbs., any lighter and I get a bit nervous.
With the DA trigger, both the mainspring and the rebound spring influence the weight. However the effect of the rebound spring is not as readily apparent as it is with the SA trigger. From the factory both my 620 and 610 had a DA pull of about 10 lbs. Installing a 14 lbs. rebound spring took the DA trigger down to about 8.5 lbs. With a 12 lbs. rebound spring the pull only dropped another 1/2 lbs., it's not a linear progression.
I've just started my experimenting with the strain screw and this has a distinct an immediate effect on the DA pull weight. Last night I made up some shims that fit under the head of the strain screw using 0.010 inch shim stock. I first tried shimming the strain screw out by 0.020 inch on my 620 and the DA trigger weight dropped into the 6 lbs. range. However, it also yielded a hammer strike that was distinctly weak and I doubt that it would prove at all reliable. Currently the 610 and 620 have 0.010 shims under the strain screw and tomorrow I plan on testing for reliable ignition with CCI/Blazer ammunition. Word on the net is the CCI's primers are the hardest to ignite, so if they prove to be reliable with CCI ammunition, they should be good for anything. DA weight is about 7.8 lbs.
Now, one additional observation. That is that with the 0.020 shim installed under the strain screw on the 620 there was almost no observable effect on the SA trigger weight. While this may seem somewhat conflicting, the coefficient of friction of steel on lubricated steel is quite low, basically it equals the sine of 7 degrees. What this means is that the increase in friction in the sear is equal to the change in pressure multiplied by the sine of 7 degrees. Quite simply, the SA pull is determined by the spring pressure on the rebound slide and mainspring pressure has very little effect.
PS, at some point I'll actually break down and get a digital trigger gage, the current fish scale I've been using is not very accurate, difficult to read, and the weights posted probably have at least 1/2 lbs. of error factor in them. However, that fish scale has been helpful in permitting to observe the effect of trying different things.
My new S&W 686 Talo Custom 7" Barrel .357 must have been made on Friday at 5 PM when everyone was ready to go home because it DOES NOT have an easy pull SA and I have measured it at more than 5.5 pounds. IT is nowhere near as crisp in SA or DA as my .44Mag Ruger Super Redhawk and I am considering taking it back to the gun store to have it checked out or sent back to S&W. I have posted my shooting results in this forum and while it is better than it was when I first got it a month ago it is nowhere near good.
