While not as experienced as a OldFluff, I am going to give a
BIG "NO" on messing with the strain screw. I am not familiar with Mr. Trzoneic as a writer I follow, and I don't know how deep his knowledge of S&W actions are. But in my experience I have learned a factory-length strain screw and factory mainspring are critical to consistent function, and improvements in trigger action or feel should be sought elsewhere (and not monkeying with trigger/hammer sear angles, either!).
1) The geometry of the screw is important to the hammer action as Old Fluff has described.
2) A more difficult, but safer way to lighten the stroke is to lighten the recoil spring.
3) I believe that Wolff warns on their web page that changing out the mainspring has a good change to result in mis-fires.
4) Loosening the strain screw removes all long-term consistency in the mainspring action:
Those with some knowledge of machine tooling and metallurgy understand that it is the torque applied when tightening a screw or bolt that determines it's security. Basically, the heat generated by the friction of the torquing "micro-welds" the two sets of threads together. If the screw is loose, it has no tension and will back out in small increments under each load.
Long action vs. short action
jad0110 - as OldFluff stated, the early guns have a different angular rotation in the hammer. This dramatically alters the trigger pressure during the firing arc of the trigger. On "short actions," the same amount of pressure has to be generated with a) the same arc of the trigger, but b) a shorter hammer arc. This change started in 1947 on the K frame and I think all models were converted to the modern "short action" by the end of 1949. The easiest way to tell the difference is to examine the hammer. The "long action" triggers have a trigger that moves back in one smooth top line, as opposed to the "notched" style characteristic of the short action. Start at the front of the hammer and let your eye trace the top silhouette. If it moves back gently, it's a long action. If it plunges down into a "V" then rises to the thumb rest, it's a short action. See the photos below for a comparison and look at the spot I am talking about. I will try to choose two photos in the same angle to make it easier, just follow the top line of the hammer and the difference is obvious. Once you see the difference, you'll be able to spot it instantly on any S&W you look at and immediately know if it's a short or long action.
The other obvious way to view this is to look at the radius of the hammer that emerges from the knuckle of the frame - see how much more of the "long action" type has to rotate backwards to meet the knuckle vs. the "short action"? As degrees of the absolute rotation about the axis it's small, but in percentage of what the thumb rotoates (or how far the firing pin has to fall to hit the primer), it's a large percentage of difference.
Another footnote is that not all "long action" mainsprings are the same. I have been told and experienced with one of my guns (a military WWI model), that military models (2nd model .455s, and war-time 1917s) were made with slightly stiffer mainsprings than commercial models to deal with harder military primers of the time. This is just a footnote for those really into this subject - and also to know that a nice way to smooth up a vintage .455 or 1917 is to switch out to modern mainspring (keeping the original stored along with the gun in an airtight bag with the s/n of the gun on a scrap of paper, of course!).
It was made to shorten the thumb-cocking stroke and please bullseye target shooters.
I was always told it was to decrease the lock time as the hammer fell, but perhaps I am wrong or maybe that is what you had in mind and said it in reference to the cocking action as opposed to the hammer fall.
1) "Long action" S&W, K frames 1899-c.1947, N frames 1909-c.1949:
2) "Short action", various frames 1947 and later:
