Now I'm getting light firing pin strikes. I didn't think bobbing the hammer would cause this?

Only bobbed it so it was "flat" where the hammer spur was
located

It doesn't. We lighten S&W revolver hammers much more than the traditional "bob" just so we can run less mainspring tension for lighter DA pulls. The lighter hammers improve ignition on centerfires.

What else did you do or work on while you were "bobbing" the hammer?

That's it. Only bobbed hammer

Could it be that I don't have the strain screw tightened all the way?

I hate to disagree, but lightening the hammer reduces the inertial mass, & can cause light strikes, simple physics. A lighter hammer actually requires more, not less force for reliable ignition.

I have bobbed many over the years and in most cases did them as part of a trigger job. Never had a light strike problem with the exception of using the lightest spring in the Wolfe kit once and even that ignited a majority of primers. Make sure the strain screw is tight and check that nothing is binding or mis-assenbled. Broker is spot on but unless something else is involved, the lack of the spur's weight should not cause light strikes. Using CCI primers?

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Ed45

I think it must be the strain screw. I'm going to re-check it when I get home

First thing that came to my mind...

Lock the strain screw all the way down. It's not always necessary but has been in most cases for me.Lots of bobbed hammers and polished actions.

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Blessed be the Lord,my Rock

I'm guessing you would have tightened the strain screw when you put the hammer back in. Did you get light strikes with factory ammo or reloads? The reduced mass may require you to do some polishing on the internals.

Check to see if the strain screw has not been ground down or cut. Even if it's tight a shortened screw could cause havoc.

Chief38

I hate to disagree, but force = mass x velocity squared.

Lightening the hammer makes it faster, and since the extra speed squared is greater than the lost mass, it has more force or energy.

To put it simply, a faster lighter hammer makes more energy than a slower heavier one - this is backed up by thousands of triggers jobs - the lightest reliable DA trigger pull can always be accomplished with a lighter hammer. - JM.

It was the strain screw.

Sorry, I'm a physicist, I have to comment.
Energy = mass * velocity squared

I think the relevant quantity is momementum = mass * velocity. The hammer hits the pin and transfers its momentum, which makes the pin move.

If you lighten the hammer (less mass) it will need to move faster (more velocity) to have the same momentum.

If you lighten the spring a heavier hammer will accelerate less, but end up with the same energy if you work out the math. The fact that a lighter hammer actually works better with a lighter spring I would guess means that there are other issues with friction that are important.

Apology accepted.

Hammer energy will be equal to the stored energy in the mainspring minus frictional losses. Hammer weight doesn't figure into it.

What you're missing is that the primers like a high velocity hit. There seems to be a velocity threshold not an energy or momentum threshold for ignition.

Not enough hammer velocity and you don't get ignition. A lighter hammer requires less mainspring tension, less stored energy, to achieve enough velocity.

We routinely lighten MIM hammers by 50% AND run less mainspring tension. Less energy and less momentum but enough hammer/firing pin velocity to ignite the primer.

If you lighten the hammer IT DOES move faster.

Sorry, I'm a gunsmith, I had to reply. - JM.

My only argument was with "force = mass x velocity squared".

I'm not arguing with your experience. I'm here to learn from it.

Having carried S&W revolvers as a Peace Officer for 30+ years my "business gun" is a 65-5 3" with bobbed hammer and a very sweet action that is 100% reliable with polished innards, Wolff springs and lot's of TLC during years of daily carry. Polishing the action assists both bobbed and non bobbed hammers; but it really shines with a bobbed hammer; the difference is obvious. Thanks to all the physicists, gunsmiths and engineers who have made S&W a great SD weapon through the last 150 or so years. BTW I shoot better DA than I do single action. More concentration on sights and trigger release

I just got done lightening a hammer on on my PPC Smith 19 and thought I would share. With a lighter hammer I can get lighter spring pressures and still retain reliable ignition by keeping the hammer velocity up 5.5- 6 lb DA pull..
Robert

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