doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com What determines trigger pull?

And how does a gunsmith lighten severely heavy pulls?
I have a nice J. Manton with massive, Birm. proofed, twist barrels in like new condition which I would like to shoot but my index finger is too weak.
The gun weighs 8 lbs 12 oz. I don't know the trigger pull since my scale only goes to 20 lbs.
Locks are bar action hammer.
I'm going to work on it myself. I believe I have the tools (spring clamps, files, stones) and similar locks from a gun with unsafe barrels to practice on, but I don't have a clear idea of the best plan of action.

tread very carefully....this is a job for a pro. One stroke too far and you will be looking for new sears. Usually when trigger pulls are that heavy the bodgers have been there first.

E-D,
Trigger pull weight is determined by a lot of factors, but, assuming a gun design is capable of good pull weight, the likely causes of excess pull weight might include:
1) sear angle
2) sear engagement (contact area)
3) incorrect sear spring pressure (replacement spring? also check interceptor spring on sidelocks)
4) binding mechanism

That's a start on a list of where I'd look.

Thanks Chuck,
Sear spring and binding sound like possibilities,although in nice condition and looking pretty, things inside are not finished to best standards.

SKB - No bodgers have been in there yet.

Try loosening the connecting screw on the locks, might be too tight causing binding.

+1!

I think JDW has an excellent thought.

If your Manton is the genuine article and the trigger pulls are as heavy as you say, then some 'bubba' has already been at it. Leave well alone and get a professional to do it for you. I will be cheaper in the long run.

Harry

Just came across this post and although late I thought I would put in my penny worth.
Generally I would agree that trigger pulls are best left to the pro but having taught myself with only the help of a sketch on a scrap of paper by a friendly gunsmith, I feel it my duty to pass on my modest experience.
Trigger pulls SHOULD BE the interaction between the angle on the sear nose, the angle on the bent and the power supplied by the main spring.
Yes, there is the issue of binding components, bodged bents, softened (or never hardened) sears but lets assume that the lock is sound, well designed and not messed with.
In essence, when you lift the sear out of the bent, it raises the tumbler ever so slightly against the main spring. Working against the main spring and sear spring and friction between the two components gives you the weight of the trigger pull.
Assuming that the sear and bent aren't corroded or gummed up, we can ignore friction as it should be reasonably constant (by the way, don't try polishing the sear or bent or your pulls may evaporate instantly!).
Firstly, clean all the components and reassemble and re-test. If there is no improvement....
So what you are trying to do is to adjust the pull weight by changing the angle of the sear nose ever so slightly to increase or decrease the amount of extra load it puts on the main spring as it moves out of the bent.
An example to explain the process is the way a door catch cams itself into the latch.
Remember, the amount you are adjusting the angle by is very slight. I use lots of magnification and a 80mm fine (read worn-out!) diamond flat file. I smoke the sear so I can see exactly how I am touching the nose and only proceed a little at a time. I always cut in the same direction as the sear will move to avoid any increase in friction.
I then rebuild the lock and gun, work the lock at least 10 times before taking a series of readings until it stabilises and then average the last 5.
With very heavy locks, I find this is often caused by the sear nose being almost a knife edge yet the bent is of normal depth. This means that the sear if having to climb Mount Everest to get out plus there is often a catch on the edge of the bent which makes the pull so heavy. In this case one needs to reduce the depth of the bent before any meaningful adjustment of pull can be undertaken. Adjusting these knife edge sears can be fun!
If you still want to have a go, don't practise on your pride and joy, find a few clunkers and mess with them first.

Having such a nice old gun, unboogered is rare indeed. Which would also indicate it is probably long overdue for a strip and clean by a double gunsmith who knows what he is doing. Were it mine I would send it to a good smith and be done with the problem.