John, once you have a "cockable bobbed hammer", you can still cock it and fire it SA. You need to start the hammer motion with the trigger is all
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This sort of configuration is for the EXPERIENCED SHOOTER ONLY!!!!!!!!!!!
Popeye has provided a graphic illustration why
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In very experienced hands, this sort of thing isn't dangerous, BUT I personally believe that even such an "experienced shooter" must switch completely to the de-cocking drill that works with hammers that don't have a firing pin on them (thumb down in front). Which means eschewing classic S&W DAs, true Colt SAAs and clones, etc. AND shooting a fair amount and doing enough dry-fire and handling drill that this decock method (thumb all the way in front of the hammer) is utterly ingrained.
That's my opinion.
I can recall one elderly gent at a range showing me his Taurus snubby with a home bob-job. I asked him if it was a true DAO conversion...he said yes. I confirmed the unloaded status, pointed it downrange, cocked it by starting it with the trigger. He was shocked, and didn't realize that was possible. I handed it to him, and he had no idea how to de-cock it. I showed him of course but this is a classic example of what happens and what people need to understand.
Another thing: say you take it all apart, figure out where the SA notch on the hammer is, and file it out to "finish the process". Cool. Are you *sure* you did that part right? Is there any possibility it could "hang up" back there with basically a 1/8th pound or so "seriously hair trigger"?
I'm not a gunsmith, so I couldn't say for sure how likely this is, but at a guess it would appear to be at least possible. At a minimum, test the hell out of it, repeatedly trying to "cock it" with pressure on the hammer from various directions.
I'm not saying "don't modify your gun", not hardly. DO be aware of consequences and things to check for. Make a deliberate decision whether or not you want to leave a "minimal SA capability" in there with a bobbed hammer and if you do, understand how to handle such a beastie. Print up a warning on a 3x5 card explaining how this gun works and how to de-cock it, seal it up in clear packing tape so it'll last basically forever, and stash said card in with the gun's container. If you die, it won't end up killing a relative/descendent/purchaser.