I think the standard spring is 17 lbs. I have had a number of Redhawks tuned by various shops and played with springs. Best I could do was a 14 lb spring. I also added the extended firing pin from Bowen and had the headspace set down around 0.063" and minimal endshake and had 0.055" firing pin protrusion. With this setup it would fire in double action WW primers, Federal and whatever CorBon uses in their ammo. As others have noted avoid CCI primers as they are the least sensitive. Also, just because it does not FTF in single action check the double action as the hammer arc and amount the spring is compressed is less so the hammer hits with less force. Bowen, when he tunes a RH, retains the stock spring.