I copied this from a post I made on another forum. Maybe it will be of some use here too. I probably should note that if you replace the mainspring with a lighter version, you may end up with failures to fire with anything other than federal primers. I measured the trigger pull before starting on this at 4 pounds in the single action mode, and roughly 13.5 pounds in the double action mode. First thing-- Disclaimer-- 1. I am not a gunsmith 2. I am not liable for any modification you perform on your gun. It is your responsibility to verify the safety and/or reliability of your gun after any modifications you perform as a result of this post. 3. I am not liable for any damage you cause to your firearm, or gunsmith fees arising from an inability to reassemble your gun as a result of this post. 4. I am not liable for any damages to people, property, or animals resulting from an unsafe condition created by any modification you perform to your firearm as a result of this post. 5. I am not liable for anything as a result of this post. Now, on to business. The first thing we want to do is verify that we have all of the proper tools and parts for the job. I ordered a Wolff trigger rebound spring kit from Midway USA, which comes with 1 each of 12 pound through 16 pound reduced power trigger rebound springs. The idea is to replace the factory trigger rebound spring with a lighter version that still provides proper function. If you put in too light of a spring, the trigger will not reliably reset to the at rest position, necessitating taking the parts back out and changing the spring to a heavier version. Something I did not do here was replace the factory mainspring for a reduced power version. I would have done this, but Midway was out of them at the time of my order. I strongly suggest that you obtain one prior to doing the work below, as it requires removal of the sideplate. Might as well do it while you're in there. Tools required-- Gunsmith screwdriver set and either a 1" diameter hardwood dowel about 12" long, or a wooden hammer handle. A cheap and very functional "gunsmith" screwdriver set is nothing more than an interchangeable bit handle and a large assortment of tips. The one below came from Walmart and cost under $15 IIRC. Optional tools are a glass of whiskey and coke, and a can of copenhagen(not fully pictured).  The patient for tonight, a S&W 2.5" 66-5 with fancy(and very slippery) wood grips The patient with it's normal Hogue Bantam grip Next, we remove the grips and verify that the gun is unloaded Now, lets examine the sideplate screws. Pick the gunsmith screwdriver or tip that fills the slot. Ideally, it should exactly fit both the width and the groove. Remove the sideplate screws and be sure to note exactly which hole each one came out of. Label them, or whatever you need to do to keep from getting them mixed up. Sideplate screws removed. Now, DO NOT PRY THE SIDEPLATE OFF!!!!! It is(almost always) very tightly fitted and doing so will damage it. Hold the gun by the barrel as shown in the picture below, over a padded surface. This is where the wood dowel or hammer handle comes in. Using said dowel/hammer handle give the grip area a few sharp raps. Chances are, it will take quite a few before the sideplate will finally dislodge itself and fall onto the padded surface. There will also be one other small L shaped part that falls out. This is the hammer block safety. Once the sideplate is off, set it and the hammer block off to the side. Pic of how to hold the gun. You should now have something that looks like this, though hopefully without the rust on the internals. This is a former police gun, so it's probably seen a lot of carrying and possibly a humid climate--or it could have been left somewhere that went through rapid heating and cooling cycles which caused condensation. The next couple of pictures show the rebound slide, which contains the rebound spring(the part I'm replacing here). This part will not just pop out, the mechanism requires further disassembly before it can be removed. Close up of the internals. Screwdriver points to rebound slide As previously stated, I still have further disassembly before I can remove this part. At this point, I need to remove the trigger and hand assembly. Do NOT pivot the hand to the rear and then pull up. There is a small spring located inside the trigger which bears against a small pin and provides positive forward(toward the muzzle) pressure to ensure that the hand is forward and rotates the cylinder. If you pull up(looking down at the gun) after pivoting the hand to the rear, the hand will pop out of the trigger and it's a real PITA to get that spring back over the arm(BTDT, not fun), not to mention getting it back in place inside the trigger should it fall out. There are several possible routes, but what follows is what I found the easiest. You should note that the silver rod seen protruding from the rear of the trigger engages the rebound slide. This part can fall out of the trigger once the trigger/hand assembly is removed from the gun. It's not spring loaded, and it's easy to put back in. The large end goes inside the trigger, with the two "lugs" in the grooves inside the rear of the trigger. To remove the trigger and hand assembly, I found it easiest to fully cock the hammer, then hold the trigger back as I lowered it. I then held the hammer forward while I inserted the thin screwdriver bit in the pic below between the hammer and the frame. This wedged the hammer forward and at the same time held the rebound slide to the rear, releasing 95% of the tension on the trigger. At this point, pivot and hold the hand to the rearwhile wiggling the trigger up and off of it's axis pin(being mindful NOT to pull the hand out of the trigger). I also had to do a bit of wiggling to get the rod to come free of the rebound slide. Pic of screwdriver bit used as wedge, with hammer and hand assembly removed and set at top left. After I removed the trigger and hand assembly from the gun, I placed my thumb on the rear of the hammer and pushed forward. I then removed the screwdriver bit and slowly released pressure from the hammer. At this point, the rebound slide begins to move forward(under a surprising amount of spring pressure) and may jump out of the gun. Once the rebound slide had been allowed to move forward it will be free and can be easily removed from the frame. I removed the factory spring from the rebound slide and set it to the side to avoid mixing it up with the new reduced power spring. Since this is a carry piece, I wanted to be sure that I chose a spring which would return the trigger with some extra oomph while still reducing the trigger pull. From the Wolff kit I selected the 14 pound spring(remember, the kit contained one each 12 pound to 16 pound springs in one pound increments). Picture of the rebound slide and spring. Picture of the spring in the rebound slide. Reinstalling the rebound slide is nearly a three handed job. I found that I needed to put my hand at the rear of the grip frame with my index finger and thumb holding the bit previously used as a wedge, and my middle finger holding the hammer slightly cocked. I then applied rearward and downward pressure to the rebound slide with my screwdriver. Once the rebound slide was far enough to the rear(reference the picture shown with the screwdriver bit used as a wedge), I pushed the hammer forward to hold it in place as I inserted the bit between the hammer and frame as before. With that accomplished, I pulled the bar from the rear of the trigger and applied a dab of grease to each of the bosses and reinserted it into the trigger, as well as a dab of grease to the trigger axis pin in the frame. I then reinstalled the trigger into the frame, making sure the hand was in it's slot in the recoil shield, and the rod went into it's proper place on the rebound slide. It took a little wiggling and jiggling to get everything to fall back into place.