Chief38 has an approach similar to mine, however I made it a habit to test for ignition reliability and it's effect on accuracy during the process. The end result is no loss in accuracy and complete reliability with any ammunition that I have been able to find.

In my model 620, I've installed a 13 lbs. rebound spring and installed 0.022 inch of shim under the head of the strain screw. Because it features a frame mounted firing pin, I was able to replace the firing pin with a slightly longer firing pin with an extra 0.015 inch of travel due to the longer travel slot. The firing pin is from Cylinder and Slide. Single Action trigger pull is 3 lbs. even and the Double Action trigger weight is 8 lbs. even.

Now, I will note that the frame mounted firing pin offers an option that isn't availble to gun with a hammer mounted firing pin. That is that you can purchase longer firing pins than what was originally supplied from the factory. Recently it seem that S&W has lengthened their firing pin to 0.495 inch which matches the length that Cylinder & Slide offers and those from Apex Tactical. I should also emphacise that the C&S firing pin does feature a longer travel slot than factory and dry firing with this firing pin without snap caps can wad up the firing pin return spring. I will also note that the C&S firing pin SHOULD NOT be used until the Double Action trigger pull has been reduced to 9 lbs. or less, otherwise it may pierce the primer and get stuck. Apex Tactical takes a slightly different path, as I understand it their firing pins are Tatanium and they also offer a lighter firing pin return spring. I've got my eye on a 627-5 at a local dealer and if it's still for sale next weekend it'll be the next revolver I tune up and I intend to try Apex Tactical's ignition kit in this gun.

Something else that I've found is that the Hammer must be factored into the equation. As odd as it may sound, a heavier Target Hammer requires MORE power from the mainspring than a lighter Service Hammer. As for why, primer ignition is a result of Kinetic Energy and since that is a product of Mass time the Square of the Velocity speed matters. Because of this IMO you can go between 1/2 to 1 lbs. lighter with the DA trigger weight with a Service hammer than you can with a Target hammer. Cut the spur off completely and you may be able to gain another 1/2 lbs. or perhaps more. Bottomline, on a modern revolver with a frame mounted firing pin, by bobbing the hammer and using in increased reliability firing pin should result in a DA trigger between 7 amd 7.5 lbs. with perfect reliability with common commercial ammunitions. If you have an older model with a Target hammer I wouldn't recomend going below 8.5 lbs on the DA trigger and 9 lbs. may be the lower limit for reliable ignition with any ammo you can find.

As for the basis, here is the list of revolvers I've been experimenting with and the resulting trigger weights at this point.

Model 620. DA trigger at 8 lbs. 0 ounces, SA trigger at 3 lbs. 0 ounces. C&S firing pin. Service hammer. 13 lbs. rebound spring.

Model 67-1. DA trigger at 9 lbs. 0 ounces, SA trigger at 3 lbs. 1 ounce. I can probably take the DA trigger to 8.5 lbs. but haven't tried this yet. Service Hammer with hammer mounted firing pin. 14 lbs. rebound spring.

Model 617 no dash. DA trigger at 9 lbs. 0 ounces, SA trigger at 2 lbs. 3 ounces. Target hammer with factory rimfire frame mounted firing pin. Ignition has only been tested with Winchester and Federal bulk ammunitions but is 100% reliable. Target hammer. 14 lbs. rebound spring. The gun was purchased used and equipped with a red dot scope, so I strongly suspect the previous owner had stoned on the SA sear on the trigger and this is why the SA trigger is so light. At some point I'll sharpen the SA sear back to the factory specification and this should result in a 3 lbs. SA trigger.

Model 610-3. DA trigger is 9 lbs. 0 ounces and SA trigger is 3 lbs. 0 ounces. At one point I tried at at 8 lbs. 0 ounces for the DA trigger and ignition failed at a 30% rate, which is how I learned that Target hammers require more power than Service hammers. C&S firing pin. Target hammer. 14 lbs. rebound spring.

Finally, commercial ammo's used to test for ignition reliability and accuracy. In 38 spl. it's been WWB, Remington, Blazer, Speer Lawman (both standard and +P), and American Eagle. In 357 Magnum it's just been American Eagle because Speer 357 Magnum is just too expensive and I haven't found any locally in the Lawman line. In the 610 it's been Federal Champion and Speer Lawman 40 S&W. I've also shot one box to 10mm Magtech but it's all I could find locally. At some point I'll order some hunting 10mm loads from Double Tap and try it out in a limited way, however my primary use for the 10mm would be for hunting and this would mainly be used in Single Action so the bulk of my testing with this ammo will be for accuracy.

As for the Rimfire, I shoot the 617 with the cheap stuff because it's accurate and cheap. Thus my choice of either the Winchester bulk or Federal bulk. However, with the chambers in the cylinder clean I have yet to experience one single misfire. Some day I'll try it with some CCI 22LR but it will just be to satisfy my curiosity. BTW, I've shot the 617 a LOT in double action rapid fire and it's a pure blast. Muzzle movement is so minimal that the only thing that limits my firing rate is how fast I can pull the trigger.