Burt Stroupe

Many of us have been griping about the weight, the lack of smoothness, and the perceived stacking of the double action trigger pull of the new Smith and Wessons with the Metal Injection Molding (MIM) parts and the frame mounted firing pins. From what has been published, I gathered that MIM parts would have something around 90% of the density of a forged part. That sort of churned around in my head for awhile, and I began wondering how significant the weight differences of MIM versus forged really was and how that would affect the trigger pull. So I decided to compare two N-frames by weighing the affected parts and comparing them visually.

To do this I decided to weigh the hammer assembly, trigger assembly, trigger return slide, mainspring and hammer block. The N-frames chosen were a Model 625-6 .45 ACP Mountain Gun (all MIM except for the hand), and a Model 24 .44 Special (all forged). The firing pin on the 625 is frame mounted and the firing pin on the Model 24 is on the hammer. Since S&W has numerous trigger widths, the table below describes the part that was measured from each revolver. The trigger assemblies included all springs, etc., and the hand, primarily because putting the hand back in the trigger is a real pain for me. Likewise the hammer assemblies included the sear, the stirrup and all springs, pins, etc.

All the above weights are in grains.

As you can see the forged hammer and trigger are about 15% heavier than the MIM parts, and the return slide is about 10% heavier. There are also some interesting differences in the parts. The main spring on the Mountain Gun is noticeably thicker at the base. However, what is really noticeable is that where the mainspring is captured at the bottom of the frame has moved considerably. On the model 625 the distance between that spot and the stock pin is about one-half what it is on the older model 24. Also, the strain screw is about 1/8th of an inch shorter in the threads, which means you can’t put as much tension on it.

What has happened here is the reciprocating mass has been reduced considerably, and there is a change in the arc through which the spring operates. To compensate for these changes, the mainspring is a lot stiffer, so the hammer will still whack the primer with enough force to set it off. If you carefully cycle both the 625 and the 24 in double action with the sideplates off, there seems to be less initial movement of the mainspring in the Model 24. My conclusion after observing this is this change in the geometry is the primary cause of the perceived increase in trigger pull. I do not own a trigger scale so all of my conclusions here are subjective. Having said that, I think the overall effort has not increased significantly, but I think the initial effort to raise the hammer and rotate the cylinder has. I think this increase in effort has been made even more noticeable by the MIM parts. I will not speculate whether this increase in trigger pull has political origins or is just a side effect of engineering changes.

I then decided to see if any improvement could be made to the 625 by using the heavier forged parts. From my small parts supply I swapped in a trigger, return slide and spring, mainspring and strain screw. The hand from the 625 was used. This took a couple of tries and several triggers in order to get the timing like it should be. Upon final reassembly, the trigger pull seemed much improved and had virtually no stacking. (Once again, this is subjective.) Now the only remaining question was reliability - so off to the range.

For the initial test, I selected 150 rounds of .45 ACP consisting of a mixture of surplus ball rounds (RA 68 headstamp) and handloads. The handloads were in a mixture of commercial and surplus cases; all were primed with Winchester Large Pistol primers. Firing double action, the first round was a very satisfying "BOOM". The second round went click. After waiting a long time, that round fired on the second try. After ejecting the two spent cases and three live rounds, I then tightened the strain screw one-half turn and the remaining 148 rounds fired with no more misfires. About one-third of the rounds were fired with full moon clips and two-thirds without.

Conclusions: Well, first of all none of what I did was necessary to the functioning of the revolver. However, it now feels like my other S&Ws – it feels almost like an old S&W. I would also like to say this is one of the most accurate revolvers I have been exposed to. Doing this parts swap has smoothed up the double action to a point where, for me, that accuracy now becomes useable. To me that is important.