I'd swear Jack Belk posted adjustment instructions on HA several months ago but can't find them, no way, no how. I believe he said they were right out of the original owner's manual.
Jack, or anyone, still have these?
Posts: 1246 | Location: Northern Virginia, USA | Registered: 02 June 2001
I found this one....... Reposted by request. ________________________________________________
I was ask by email about this today. As (bad) luck would have it I also was contacted by an attorney concerning the death of a kid involving a M-70.
According to the lawyer, "..........the uncle adjusted the trigger by internet instructions". It was a bad accident waiting to happen. And, tragically, it did.
As a result, I answered the email in detail and decided to post it here, also.
I'd rather not start a pissin match with those that do it differently or believe something else to be true. Facts are facts. If you have physics and engineering reality on your side, please post it.
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Trigger pull has two components to it....friction and spring tension. The two nuts on a Model 70, control the spring tension on the parts. Ideally any trigger will have half and half. This is especially important in a trigger that is unbalanced to the bottom side of the pivot, like the M-70 is.
DON'T mess with the trigger sear surfaces except with lapping compound. Those surfaces HAVE to be perfectly flat and square to be stable. ........think of it in BIG terms....like two big squares of concrete, one on top of the other. If they're sitting level and flat and square they're tough to move, but if they're rounded any at all they will rock and pivot and be very insecure......and that's bad. That means the gun can fire when it's bumped or dropped.
An over-ride trigger acts like an earthquake. It should build tension until the break point, and then break all at once.
Visualize a graph with the movement in thousandths up the left side and pounds of pressure on the trigger across the bottom.
The trigger shouldn't move (ideally) until the entire amount of pressure is applied to break the sear-trigger interface. The graphed line will look horizontal out to where about 3 pounds is located on the graph and then the line shoots straight up as the trigger moves the entire .015 to .020 of sear engagement and the several thousandths of overtravel.
To do that the surfaces have to be flat, square with each other, AND geometrically balanced to the arc of rotation. They also have to be metallurgically clean, smooth, and uniform. The trigger and sear parts have to be hard enough to take pressure and wear without galling and rounding, but not so hard the sharp corners will flake or fracture. You can't do that by hand just like you can't facet a stone by holding the abrasive in your hands and the stone in the vice. It can't be done. The part has to ride on the abrasive, not visa versa. Our bodies are made for flexibility, not mechanical repeatability.
To adjust a Model 70 trigger
Disassemble and brush clean all the parts. Lightly oil (the proper amount of oil, if applied to a shot glass won’t spoil whiskey) all the parts.
Leave the trigger return spring completely out of the gun and using your thumb to reset the trigger into the proper position, measure the trigger pull. It should be AT LEAST 1.5 pounds for a M-70.
Now put the spring back in and adjust it until it takes AT LEAST two pounds to pull the trigger WITHOUT the bolt in the gun. You'll have to look at the trigger and the scale to see when to read this pull. The trigger only moves about .025”.
Now measure them together. THAT is the lightest, safe trigger pull for that gun.
If the trigger pull is gritty or has hitches in it, use a tiny dab of 320 lapping compound or 600 mesh diamond paste on the sear face and dry fire the rifle about ten times. Measure the pull without the spring again. It should be smoother and lighter. DON'T allow it to go below a pound and a half.
It takes about 200 Gs to overcome the weight of the trigger piece below the pivot point to overcome 1.5 pounds of mechanical friction of the sear and trigger and two pounds of coil spring force.
A drop of 25 feet or so will fire a Model 70 if it lands butt down.
That distance is reduced DRASTICALLY when the frictional forces aren't sufficient......sometimes to inches.
