The SST mechanisms on the vintage guns are generally Ok if they have never been messed with and the stock itself hasn't been the subject of removal, rebedding, oil-soaked wood, things like that.
The distance betw the upper and lower tang means a great deal. Simply put, wether they work or do not work.
In the do-not-work list it can be a bunch of different configuration of issues and then some not all the time.
The fact that you can often bring a faulty SST mechanism back from the dead by mearly tightening and or loosening the top tang, rear tang and sometimes the trigger plate screw as well is fairly well known.
It's not really a fix, it does show that there's something at least wrong with the stock bedding in relation to the tangs.
There are so many things that these mechanisms depend on to be stable to function correctly that by looking at the mechanism in hand I wonder how it often works at all.
The parts are generally crude,,any linkage connecting pins betw them are loose fitting looking for all the world like snippets of common nails an lightly peened over on each end to keep them from falleing free. The holes in the parts are that sloppy that slide through.
Here's a little on how the Hunter One-Trigger operates and what needs to be right for it to function correctly.
There's a lot more to it than just this, but it can show where the frustration can come from when someone sits down thinking they will
simply go through it, clean it up and it should be A-OK good to go.
Many don't realize that the rear end of the Sear Arm(s) themselves plays a part in the selection of the bbl to be fired in Hunter One Trig.
The very first contact of the pulled trigger against the selected sear pushes the Hook Shaped element part in the mechanism to the rear.
I have no idea what the real name of that part is, I guess I don't care.
A very fine wire spring gives that Hook it's tension to sit forward and out of contact. As soon as the Sear Arm makes contact with selected sear arm,,the Hook moves to the rear. As the trigger continues to be pulled and the Sear elevated to release the hammer,,that Hook is a limiting devise as far as how far the Trigger can be pulled rearward.
In it's rear position it is under an overhanging shelf of a part that it will engage as the trigger is continued to be pulled.
Once engaged, that is the limit of the trigger pull on the Selected Side.
So. the selected bbl/Sear-Hammer must release/fire before that limit of travel is reached.
That limit of travel is in place to avoid the Trigger from travelling too high and engaging the opposite bbl sear arm (unselected side) and firing it as well (Doubling).
The difference in height betw the two sides is the Selector moved into position by the shooter.
Once the selected bbl is fired, that sear arm must be designed to move upwards and away from the trigger mechanism so it does not once again engage the Hook.
If that Hook stays engaged, then the overall trigger pull distance is again limited to what it was on the Selected BBl side.
That's been done,,it now needs to be out of the way so the trigger can be lifter higher to fire the unselcted side/bbl.
Getting the hook out of the way and disengaged is done by profiling the area on the hammer behind the sear notch to be an upward travel ramp of sorts.
The (fired) Sear nose will follow along it as the hammer drops and the tail of the sear arm will end up raised and out of the way. The Hook retreats back from underneath it's travel limiting 'overhanging shelf' part (again I don't know what the part is called actually.
Now with a release of the trigger, it resets as the Hook disengages from it's limiting stop and is now out of the way.
The trigger under it's own spring power moves upward but only a very small distance till the unselected side of the Selector engages the underside of the second bbl.
A second pull on the trigger fires the second bbl.
If the Sear arms are out of wack as far as their height above the selector,,the mechanism will fail in one way or another.
If they are too low,,the Selector may not be able to slide under the tail of one or both sear arms.
If they are too high, it may take too much Trigger Travel to actually release/fire a bbl and that side won't fire no matter how hard you tug on the trigger.
If both sides are high enough to allow easy Selection, and the gun doubles on one selection but not the other,,the unselected side Sear Arm is somewhere betw being too high,,and too low.
Don't forget to make sure the Safety engages securely and the anti doubling swinging weight is working as well.
Two other things that can make for problems in this mechanism, but I won't get into them.
This stuff is all pretty easy to do with on the gun With-Out the stock being on it.
You've likely seen some with those plier teeth marks on the tail end of the sear arms. Thats generally where they were 'carefully adjusted for height and sometimes even bent downward or up at the tip.
All your adjustments done, you put the stock back on and tighten 'er up....it doesn't work.
Probably different or more issues than before.
W/O the stock on the action, the SST can work great with some adjustments and tweeks.
But once tied up in it's stock, those tangs and plate bend quite a bit and throw the positions of parts way off. Then things don't work,,but you are in the dark. Being able to only experience the failures and sometimes hear what's going on.
Here's where many 'smiths start fiddling with the tang screws and the trigger plate screw to get it to 'work.
That leaves the stock head loose even a little and it's a poor excuse for a repair job.
You have to do these with the stock in place and tightened up.
You have to have a very good understanding of how the mechanism works to begin with, before you even start to 'repair' one..
Making changes & alterations to parts in blind attempts to make it work, or work better is doomed to failure.
You have to go by experience and 'feel' to get an idea of what is happening inside when they balk at doing a certain function.
Then know what to do to correct it when you take the thing apart once again,,and again,,and again.
Getting the stock and action firmly (re)bedded so the tang screws return to the same place each time goes a long way towards success in this.
Using steel or brass tube pillars in the rebedding process around the screws is very helpfull.
The same thing goes for repairing a Parker , Fox , Win21 or any of the SST mechanism.
Yes they all can, and do fail.
..and don't expect the best, crisp trigger pulls from most vintage SST mechanisms. There's just too many links to get to the end of the line to disengage the sear from the hammer. Plus most are not anyway near a precision mechanism.
There will be some that are a trying to be a shining star in that respect. But not generally.
Sorry for the long post..
