I have a S&W model 36 that I had bobbed....I took about half of the spur off. Turned out to be a bad idea. The bobbed hammer failed to ignite the majority of rounds that were loaded. I tried all kinds of factory fresh ammunition and it was completely random as to which cylinder failed to fire. Wound up having to put a new full hammer back on.
Did it fire reliable before you cut the spur off? Did you change the mainspring?