I use a coin for this kind of dry-firing. I've passed through it. I am on the stressed, scan, draw then dry-fire exercises. My husband and I timed one another on how fast each of us can draw.If you have a friend, they taught us this drill up at the Sig Academy:
Stand with your arms outstretched as if you are going to fire with your gun as close to a wall as you can get. Have your friend place a shell casing on top of your pistol. Now try and dry fire your weapon 5 straight times without the shell casing falling off your gun. If it falls, start over until you can do it 5 straight times. Great drill on keeping a steady trigger pull. I don't bother with snap caps, all the instructors including an R and D guy said dry firing will not hurt my Sig.