by Tom Gaylord
Writing as B.B. Pelletier

Diana 27
Michael’s Winchester 427 is a Diana model 27 by another name. The rifle pictured is my Hy Score 807/Diana 27.

Part 1
Part 2
Part 3
Part 4
Part 5

A history of airguns

This report covers:

  • Assembling the ball bearing cages
  • Two cages — inner and outer
  • The real sear
  • Trigger assembly
  • Finish the assembly
  • Trigger adjustment
  • Test the rifle
  • Summary

And I’m going to pick it up right where we left off on Friday. A reminder that I am in Las Vegas at the SHOT Show today and will not be able to respond to comments as easily as normal. Let’s get started.

Assembling the ball bearing cages

We have come to the most daunting part of the assembly — assembling the trigger unit. You have to put a swarm of loose parts into the spring tube under tension from both the mainspring and the trigger spring. First, put the lubricated spring guide into the rear of the mainspring. I forgot to do that the first time through and I assembled the rifle without the guide. Got the rifle all buttoned up and said those famous last words, “I hope I never have to do THAT again!” Then my eyes fell on the guide sitting on the table. It was smiling at me, and I’m pretty sure I heard God laugh a little!

I then had to disassemble the rifle again to this same place. Okay, enough whining, let’s get on with it! This is the point at which the parts of the trigger go together. Hang with me — there are a lot of them and several tricks are needed to get them into the rifle. Let’s look at the parts.

Two cages — inner and outer

The trigger has two cages — an inner black one and an outer silver one. Someone commented on the amazing precision that the parts of this trigger were built to when I showed how it works in Part 2. But the truth is the tolerances between the parts don’t have to be that close. The three ball bearings take care of that.

Diana 27 inner cage
Here is the inner black ball-bearing cage. As you can see, is just a thick piece of steel that’s been rolled into a cylinder. Notice the uneven join line in the seam. Not a lot of precision here — just enough to make it work!

To get the ball bearings to stay inside the black cage and not fall out during assembly, smear a lot of TIAT into each of their holes before pushing them in. It works perfectly!

Diana 27 ball in cage
Here you see one ball bearing (arrow) has been pushed into its hole that is filled with TIAT grease. That grease is so tacky that the ball will not fall out during assembly, yet it will operate smoothly forever after.

Now, let’s look at how the two cages go together. The black inner cage slips inside the silver outer cage. When the piston rod comes back, it passes through the inner cage. The knob on the end of the piston rod pushes the balls up out of its way.

Diana 27 piston rod end
You can see in this picture how the piston rod end pushes the three balls out of its way when the gun is cocked. The silver cage on the outside presses the balls against the backside of the piston until the trigger releases it.

The real sear

The silver outer cage is what holds the three ball bearings against the piston knob once the gun is cocked. It is the real sear of this rifle’s trigger. The powerful mainspring is pushing on the piston but the three balls are resting against the back side of the piston rod knob, holding it still. But, when the trigger hooks release the silver cage, it is pushed forward by the trigger spring, releasing the balls and the piston is suddenly free to move. Let’s look at the part that is the real sear for this trigger.

Diana 27 cage step
That “step” (arrow) on the silver cage is where one side of the trigger spring presses. You can even see the semicircle left by the spring on the step. The hooks that I told you are on the trigger mechanism keep the silver cage from moving, but when the trigger blade pulls them away, the trigger spring pushes the silver cage away from the black cage, releasing the three ball bearings that then release the piston.

Diana 27 cages and spring
Here you can see the two cages with the trigger spring that pushes them apart. When these parts are inside the spring tube, the trigger spring is not bowed up in the center like this because there is no room for it to be. See that indent in the silver cage (arrow)? There are three of them around the cage. They form the base that pushes against the bottom of the spring guide, and the short ramp you see on the right of the indent is what pushes against the three ball bearings that are trying to pop out of the inner cage. This is how the Diana trigger works!

Trigger assembly

The balls go in the inner cage, then the two cages go together. The silver cage is also what pushes against the spring guide inside the rifle. The last thing to put in the assembly is the trigger spring. The trigger spring in Michael’s rifle is very strong so it doesn’t want to stay in place. It wants to push the two cages completely apart, but I have a trick for that.

Now the entire rifle is put in the mainspring compressor, with one end of the compressor pushing against the rear of the trigger assembly (the black inner cage) and the muzzle of the barrel pushing against the other end of the compressor. And, here is my trick for installing the strong trigger spring. As tension from the compressor builds against the black inner cage, the two cages start to slide together. At this point the trigger must be pulled to allow the silver cage to go deeper into the spring tube. I stick a pin through the trigger mechanism (after it has been pulled) to block the trigger blade in place so I don’t have to hold it while I’m doing all this other stuff. If you don’t, you’ll need four hands to put this rifle together.

Now I install the trigger spring, mounting it to contact the step in the silver outer cage. Then I use a screwdriver inserted into the coils on the other end of the trigger spring to compress the spring back to connect with the step on the inner cage. Look at the picture that shows this better.

Diana 27 trigger going into tube
In this photo I have wound the compressor in just enough that the spring tube is now pushing down on the trigger spring, holding it in place. I had to go just a little farther than the text describes to take this picture or the trigger spring would have popped out of place. This really shows how the spring tube holds all those loose pieces together, once they are inside!

Finish the assembly

Keep winding the screw on the mainspring compressor and the parts will slowly go into the spring tube. The black inner cage will stick out a little when the gun is completely together. What you are looking for is the holes in the inner black cage aligning with the holes in the spring tube. When they do you can insert the two crosspins that hold the action together. The rear pin is slightly fatter and also slightly shorter than the front pin, so it will not go in the front spring tube hole. The pins slip in easily once the holes are aligned. Then put the metal end cap back on the spring tube and the action is assembled.

Now the barreled action can be installed in the stock and the job is complete. I have more to say, but before I get to that, let’s adjust the trigger.

Trigger adjustment

The Diana ball-bearing trigger can be adjusted to a very fine release. Because of how it is designed, you will always have a long first stage pull and there will be significant resistance in the trigger blade. But there is a definite stop at stage two when everything is right.

Here are simple instructions for adjusting the vintage Diana 25/27/35/50 ball-bearing triggers that have two screws. The front screw is just a lock screw. Loosen it, and then turn the rear screw in as far as it will go (that’s clockwise). Then, turn it back out two full turns and try cocking the rifle. Be careful not to let go of the barrel, because some guns may be adjusted to the razor’s edge this way. If yours is and you need a little more sear engagement, try turning the screw out just another quarter turn until the sear holds well. When you get it adjusted where you want it, tighten the front screw and the job is done. You’ll have a long first stage followed by a definite stop and a crisp stage-two break when the gun fires. You have to experience one of these triggers adjusted correctly to know how nice they are.

What can’t be controlled is the length of the first stage. It has to be long, if you want that crisp second-stage release. I don’t mind that one bit, though it is different than the trigger on any other airgun I can think of.

Michael’s trigger was adjusted pretty well when I first tried it, but I felt it could be just that little bit better. I adjusted it following the directions above and discovered that his trigger wants the adjustment screw less than one full turn out from all the way in.

When I finished the first stage has a resistance of one pound 13 ounces. Stage two breaks at one pound 15 ounces. That’s correct — stage two is a two-ounce trigger pull! This is not untypical. But it is a good job, if I do say so myself.

Test the rifle

Of course the first thing to do after assembly is to try to cock the rifle and shoot it. I did that and was rewarded by a loud bang with smoke coming out of the barrel. Of course, the leather piston seal has excess oil and it needs to be shot out. That will be my next duty, followed by a velocity test, followed by an accuracy test.

I can tell right now that I used exactly enough TIAT. The rifle now shoots dead calm, and with the trigger breaking so well, it is a delight to shoot. Well, after all, it is a Diana 27!


This overhaul has been an interesting foray into the world of the Diana 27. This rebuild is better than the one I did on my own 27 more than two decades ago, because Tune in an Tube did not exist back then. I used white Lithium grease. And I couldn’t get the leather seal off my piston, so it still has the factory piston seal from the 1970s.

Michael’s rifle still has some flaws I will not be able to correct, like it’s missing one of the two rear sight screws that holds it tight to the barrel and it’s missing the rubber bumper for the butt.

I have ordered a locking screw for the pivot bolt from Chambers and it should be here shortly after I return from SHOT. And, as long as I was doing that I bought a new synthetic breech seal that the Winchester 427 had. My leather seal isn’t that pretty, though it does seem to work quite well.

I may have to use a different rear sight to get Michael’s rifle through the accuracy test. We shall see. This has been a fascinating trip down memory lane for me, as I hope it has been for all of you.