by Tom Gaylord
Writing as B.B. Pelletier

Diana 5V pistol
Diana model 5V pellet pistol.

Part 1
Part 2

A history of airguns

This report covers:

  • 5 screws
  • Gun fell apart!
  • The solution!
  • Case-hardened parts
  • Stoning is out!
  • Back to the pistol
  • Testing the trigger
  • Job done

This one will be a quickie. You will remember that I wanted to remove the grip from my Diana 5V pellet pistol to see if I could do anything to reduce the trigger pull that was over 12 pounds. Well I did, and in less time than it will take me to write this short report, I discovered and corrected the problem.

5 screws

The grip is held to the action by 4 screws. They sit two to a side. The fifth screw is a wood screw that holds the base of the triggerguard to the grip. The front of the triggerguard is hooked over a pin in the action. If you don’t remove this screw first, the grip won’t come off the action.

Diana 5V pistol triggerguard
Step one is to remove the triggerguard.

The side screws came out easily and each had a lockwasher underneath. Then the grip slipped down and off the mechanism. A reader had told me that the trigger return spring was inside the grip. I found it right where he said to look.

Diana 5V pistol trigger spring
There is the trigger spring — right where it should be.

This spring presses up on what I will call the sear. It’s the bar that releases the piston. To do that it moves by pivoting down. The trigger pushes the front end of it up to make this happen. I will show that in a moment.

Gun fell apart!

The trigger and sear are held in the action by two pins. These pins are loose in their holes and held captive by the wooden grip. Once the grip is off the action, the pins fall out and the trigger literally falls apart! That’s a good thing, because it makes it easy to disassemble. And it is dirt-simple. Just a trigger, a sear, the two pins they rotate on and that spring.

Diana 5V pistol action
Two pins (arrows) hold the trigger and sear in the action. Both are loose and fall out on their own. The grip keeps them in.

Diana 5V pistol trigger and sear
With the trigger and sear outside the action, you can see how they work. The trigger pushes the front of the sear up, which makes the rear drop away from the piston it’s holding.

The solution!

When the sear fell out of the action I saw the problem immediately. It had been installed in the action upside-down! There is a cutout on one side where the trigger spring fits, but that side wasn’t where it should have been. Not only did that allow the trigger spring to press harder on the sear, it also put the wrong part of the sear against the piston.

Diana 5V pistol sear
This is the way the sear is supposed to be in the pistol. The spring fits into the cutout on the right. Notice the rear of the sear has two different angles (on the right end). The wrong one was pressed against the piston when the gun was cocked. That was where the hard trigger pull came from.

Case-hardened parts

Before we proceed I want to talk about the sear for a moment. The picture shows that it is case-hardened. That is the mottled look you see on the side and bottom of the part. Case-hardening is a way to harden steel parts that have a low carbon content, such as 1018 and 1020 steel. Carbon is the main element that makes steel able to be hardened, and if there isn’t enough of it the steel can never be hardened by heat treating. But steel with enough carbon to harden is more expensive than low-carbon steel. and case-hardening allows manufacturers to use materials that are less expensive but can be made to do a job just as well.

Case-hardening infuses a thin shell of carbon into the outside of a steel part, to allow it to become hard. The mottled appearance is incidental, though on some parts that show it can be enhanced to become attractive color case hardening.

The shell of hardened steel can be from a few thousandths of an inch thick up to several hundredths of an inch. The thickness depends on the process. The point is, the shell is thin and underneath is the same carbon-poor steel that is unharden-able. If the shell is ground away for any reason, the part underneath is soft and will wear rapidly. Case-hardened steel parts rubbing against case-hardened steel parts will not wear through the shells in a lifetime, unless an abrasive that is harder is present. The shells will wear until they are shiny silver, and that is as far as it will go. In the picture of the sear you can see a shiny line on the left, at the round place where the trigger has worn away the case colors.

Stoning is out!

For this reason, never stone, grind, sand or file a case-hardened part. Leave them alone, so the hardened case remains intact.

Back to the pistol

In this case (wocka, wocka!), all that was required was to put the parts together in the right order. I knew that the moment I saw the hollow in the sear for the trigger spring. But, I am an airgunner, so I applied some moly grease to the two places where there is contact — one on the piston and the other on the end of the sear that touches it. Then I put all the parts together and slipped the grip back on the action. The entire job took me 15 minutes — start to finish — and that includes taking the pictures..

Testing the trigger

I knew this was going to work, because I have seen it work many times before. But I was still as curious as anyone would be. So I cocked and loaded the pistol and squeezed off the first round. And it worked! How much of the new lighter pull  is due to the moly grease is anyone’s guess, but at least it does no harm.

The single-stage trigger now breaks cleanly at 2 lbs. 13 oz. That may sound heavy to someone who is used to a 10-meter rifle trigger, but on a pistol, that’s a very light pull.

Job done

I wish they all turned out this well! The trigger is now fixed and I can proceed to the accuracy test. Stay tuned!