Did a bit of planned smithing on two of my revolvers this morning. Item one was to replace the Target width hammer on my 610-3 with a 0.400 service width hammer. Item two was to replace both the hammer and trigger in my 625 JM with blued MIM parts in 0.400 widths.

Because of this I had purchased 2 seperate 0.400 inch service width hammer assemblies which included the DA sear. These parts come with a sharp tip on the sear where it engages the DA sear step on the trigger and this tip must be fitted to the trigger in order for the trigger to reset consistently. Basically, if you leave the Sear on the hammer sharp you'll find that the trigger won't reset on every return.

Since I've never managed to get my "material putter backer" to work I approach tasks like this with a Less is Better approach. After spending some time studying how the lockwork functions in double action I realized that if this sear tip is chamfered too much it will allow the hammer to release a touch earlier in the trigger stroke. So, in fitting the hammer sear to the trigger I was careful to only chamfer the tip to the point where the trigger was resetting properly and not go any further. The end result is that the chamfer is about 0.010 narrower than the chamfer on the factory supplied hammer sear.

Testing has revealed that my 625 JM now drops the cylinder stop just a bit earlier in relation to the hammer fall than it did as set up by the factory. What is actually happening is that the sear is releasing the hammer a hair later in it's stroke however the effect is the stop drops a bit earlier. It's not a lot and likely not enough to matter one bit, however it does point that there are "tuning points" in the lockwork that can effect the timing. Quite simply, if you're fitting a new hammer sear to the trigger you can cause "late" timing if you go too far.

PS; for those curious about the changes I've made, it's simply a matter of fitting the gun to myself. I like the .400 smooth trigger and now have that trigger installed in my 610, 620, and 625. As for the hammer change in the 610 it's an experiment. With the .400 wide hammer on the 620 and 625 I've been able to get 100% reliable ignition in double action with an 8lbs. 0 ounce DA trigger. With the 610 I start seeing misfires with the trigger set this light, so I installed the narrower hammer to see if that will allow me to tune the trigger to 8 lbs. on the 610.

BTW, the 625 JM was delivered from the factory with a flash chromed Forged trigger and a flash chromed MIM hammer. Obviously I was incorrect in my assumption that a Forged trigger always meant a Forged hammer because it's apparent that S&W is mixing these parts on some models.

The chamfer on the corner of the sear (the only factory "fitting" you see on an MIM hammer assy) just allows the sear to "re-set" sooner as the trigger returns. If you watch the hammer/trigger relationship as the trigger moves the hammer back DA you'll see the sear provides the initial hammer movement but the final movement and release of the hammer is controlled by fixed surfaces on the trigger and hammer. It's akin to two gears shifting contact from one tooth to the next as they rotate.

Your cylinder stop timing most likely changed because the new trigger interacts slightly differently with the cylinder stop.

Lighter hammers will allow lighter mainspring tensions for lighter DA pulls.

I like the .400 smooth triggers too.

They do play mix and match and it's not consistent. If you're unsure looking at the assembled gun pull the side plate and check the hammer and trigger for cross pins. No cross pins, they're MIM.