The way the factory used to teach it at armorer's schools is to file the mainspring strain screw, always keeping it tight against the spring when checking the DA pull weright. (work on the cheapest part). The use of moon clips has always required a bit more "ummph" from the hammer fall than when using cartridges that don't need them. The clips require more clearence between the shield at the rear of the cylinder (on the frame) and also bounce around some, thus soaking up a bit of the hammer fall. The .45acp guns are well known for this, and I have no reason to beleve that the 10mm / .40's are any different. The old time serious wheelgunners sometimes actually cut three coils off of a standard return spring and ADD them to the standard one, making the trigger return faster. Remember that the trigger return spring has almost nothing to do with the DA pull...if you are getting DA misfires it is most likely because your hammer tension is too light or, maybe, the firing pin potrusion (sp?) is a bit short, etc. Have you cut the spur off of the hammer? That will lighten it and can cause issues as well.