All things being equal, I prefer the hammer mounted firing pin to the current frame mounted. A direct strike ignition system imparts more Kinetic energy directly to the primer, as the hammer fall energy is not dissipated through transfer bars and transfer mechanisms. In marginal conditions a direct strike mechanism will ignite a primer when a frame mounted mechanism won't.
See the difference:
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My 586, the previous owner shot over 60,000 rounds of 148 LWC and 2.7 grains Bullseye in PPC competition. Besides finish wear, the main spring needed replacing.
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Having both K frame and L frame pistols
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The K frame is more compact and easy to carry. The greatest problem the K frames had was with 125 grain full bore 357 Magnum loads. The heat and probably pressure, were such that forcing cone cracks became a problem. I know one shooter who was shooting major loads in his K frame and his forcing cone cracked. If you fire 38 Special level loads the pistol will last, effectively, forever. The same shooter, a 10 times PPC Champ, has fired over 600,000 rounds of 148 LWC 2..7 grains Bullseye in another K frame S&W. He has had to replace a broken firing pin, an extractor star and cylinder hand. The cylinder and frame are still fine. Barrel still groups 2 inches at 50 yards. I have fired cases of 38 Special +P through this pistol, outside of massive lead rings in the cylinders, everything is still perfect. I have fired ammunition cans of 158 grain L or JHP with 13.5 grains 2400 and had no problems what so ever.
If on your selection criteria, compactness rates higher than high rate of fire durability, than the M19 is the better choice. But, I will say, given the same price, and if compactness is not a particularly high issue, I would go for the M586.