S&W .38 spcl revolver, 4 screw around 1920.

[Marlin 45 carbine]

took it down for new mainspring, it's completely cleaned. single action is fine but double action the trigger will hang up with hammer back just a short way. it's not the cylinder, hand or rachet, it's somewhere in the action
any ideas, suggestions, advice appreciated.

 

[1911Tuner]

Is the trigger nose pulling the cylinder stop bolt down into the frame?

 

[Marlin 45 carbine]

yes it is. it looks to me upon closer inspection w/a magnifying glass that the 'hook' on the back side (rear) of the trrigger is jamming on the bottom lip of the hammer?

 

[1911Tuner]

jamming on the bottom lip of the hammer?

That's the double action sear. Does the sear move freely when you push backward on it? Should be spring loaded and return to position.

Will the hammer make full travel if you cock it? If it won't, try pulling back firmly on the cylinder latch while you try to cycle it DA and SA.

 

[rcmodel]

Make sure the strain screw is the proper length and tight.

You can get hammer stirrup/mainspring hook contact on the underside of the hammer that acts like that if it isn't.

rc

 

[Marlin 45 carbine]

yes, it is a DA hang-up. the SA is fine, hammer -pulls back to engage the sear freely and locks firmly, releases crisply when the trigger is squeezed. seems pefectly safe to shoot in SA, and the strain screw is tight enuff there is no interference of the 'hook' of the mainspring and the underside of the hammer.
it seems that the trigger is hitting the edge of 'secondary hammer catch' or the DA catch just barely, I'm not sure what it's called. the DA sear is traveling fine it seems, not sticking at all. I backed off the strain screw a good bit and it seems to help the problem but backing off too far off course and lthe 'hook' makes contact with the underside of the hammer.
the hand and star seem fine I'm almost certain that is not the problem as well as the cyl lock travel
thanks for any tips.
I checked 'old west gunsmith' site and looked over the schematic of the revolver and parts so at least I'm aware of the parts of the actiob

 

[1911Tuner]

That's an odd one. It'd probably require being able to actually have hands on it to figure it out.

 

[MrBorland]

it seems that the trigger is hitting the edge of 'secondary hammer catch' or the DA catch just barely,

Sounds like there's too much let-out on the DA sear, in which case the trigger pushes on the DA sear too late in the cycle, resulting in a rough transition to the 2° sear (is that what it's called?).

AFAIK, one takes material off the top/back of the sear to increase letoff, so decreasing it may require a new sear. 1911Tuner & rcmodel would know.

 

[Marlin 45 carbine]

AFAIK, one takes material off the top/back of the sear to increase letoff, so decreasing it may require a new sear

as near I can tell the da sear need to be longer - contact the trigger surface to hold it down a bit so clearnce for the da will allow engagement.
thanks for tips.

 

[Jim K]

It sounds like the DA cam on the trigger is contacting the front of the hammer below the SA notch rather than sliding under that part of the hammer. The secret of S&W's non-stacking DA pull is that cam interaction which changes the leverage of the trigger pull as the hammer moves back. That should not change just from cleaning the gun, and I can't think of any way anything could be put back in wrong that would cause the surfaces to get out of alignment. It usually happens when someone decides to "smooth up" the sear and/or the trigger, not knowing how the whole system works.

Note that that gun uses the old type sear which is the width of the hammer and fits down over a boss on the hammer, rather than the newer type which is narrower and fits into a slot in the hammer. If ordering parts, make sure to get the right kind.

Jim

 

[StrawHat]

Just a reminder, the older S&Ws had a long action and repairs or tuning is subtly different than that used on the short actions of post WWII.

 

[MrBorland]

It sounds like the DA cam on the trigger is contacting the front of the hammer below the SA notch rather than sliding under that part of the hammer.

Agreed, and why I thought there might be too much let out. Agreed, though, that too much material may have been taken off the nose of the sear when tuning. Either will give the appearance of too much distance between the sear and trigger, with a rough cam transition. And either way, the DA sear is likely the culprit.