by Tom Gaylord
Writing as B.B. Pelletier

Part 1
Part 2
Part 3
Part 4
Part 5
Part 6

RWS Diana 45 air rifle
Diana 45 is a large breakbarrel spring rifle.

This report covers:

• Barrel must go on
• Piston into the tube
• Piston liner and cocking shoe go in
• Install the barrel
• Install the trigger
• Install the barreled action in the stock
• Quick function test

Barrel must go on
I’ll pick up where I left off in the last report. To assemble the parts, the barrel has to go on the spring tube. During disassembly, I’d noticed during that the breech seal was flattened and hard, so it was replaced before anything else was done. It’s just an o-ring with a steel spacer underneath, so the old one was pried out and a new one was pressed into the groove.

Diana 45 breech seal
The old breech seal is out and the new one is in.

Now, the barrel goes onto the spring tube. This is necessary because I’ll put the barreled action back into the mainspring compressor to assemble the gun, and the barrel needs to be on for that. The cocking link that’s connected to the baseblock on the barrel must be connected to the sliding piston shoe at this time, or the parts cannot be assembled. So, a number of things must happen in sequence.

Piston into the tube
First, the piston goes into the spring tube. The buttons hung up on some cutouts in the spring tube and had to be forced past them, which sliced off a portion of one button. Fortunately, no great damage was done. Those cutouts are the reason that I don’t think a circular piston ring of Delrin will work in this rifle.

Diana 45 inside spring tube
The inside of the spring tube has several cutouts that caused problems when installing the piston. Once the buttons were past them, the piston slid smoothly and was still very tight in the tube.

Piston liner and cocking shoe go in
Once the piston is in, the piston liner and cocking shoe go in. Now, you’ll see why I lubed the liner.

Diana 45 cocking shoe
Remember this part? It’s smaller than the cocking slot in the piston, so the black piston liner is what holds it in place. During assembly the shoe goes into the piston. Then, it’s raised to this level, and the piston liner is slid underneath it.

To install the piston liner and cocking shoe, the shoe needs to go on top of the liner as the liner slides into the piston. The shoe doesn’t fit through the spring tube cocking slot without tilting it sideways, so do that and then level it out when it’s inside the piston. Pull it up so it’s stopped by the spring tube cocking slot. Now, slide the piston liner into the piston until the front edge of the cocking shoe is above the piston liner. Once I got the liner started, I held the shoe in place with a screwdriver as I pushed in the liner under it. The greased liner came in handy at this point.

Diana 45 piston liner slides under cocking shoe
The cocking shoe is held in place by a screwdriver, while the piston liner slides underneath.

If you were confused by my description of how to install the cocking shoe — good! I hope you never have to do it. This procedure is like building a ship in a bottle and is one of several reasons why I do not recommend the Diana 45 as a first-time airgun tuning project.

Next, drop in the washer that goes in the end of the piston liner. Push the lubricated mainspring into the liner and piston. The spring will seat the washer square at the end of the liner. Now, we can connect the barrel again.

Install the barrel
The first step is to connect the free end of the cocking link on the barrel to the cocking shoe. They just fit together without fasteners, but the fit is very tight. Once together, they won’t come apart — once the barrel is fastened in place.

Diana 45 cocking link connects to cocking shoe
The cocking link has a notch on the end that locks into the cocking shoe.

Once the link is locked to the shoe, you can move the barrel so the pivot hole in the baseblock aligns with the holes in the action forks. Before slipping the baseblock into the forks, coat both baseblock washers with moly. That holds them in place during installation, and it also lubricates the sides of the baseblock when the barrel pivots.

Diana 45  lube base block washers
Lube the baseblock washers with moly and install them in the block. Remember — each side has a different shape!

Now, lube the pivot bushing and slide it into the pivot hole

Diana 45 lube pivot bushing
Lube the pivot bushing with moly and slide it into the pivot hole.

Now, the pivot bolt gets lubricated with moly. Most breakbarrel guns don’t have a pivot bushing. The pivot bolt serves as the axle on which the barrel pivots. There’s no special advantage to having a separate bushing like this, but it does increase the number of parts you have to deal with and makes the gun more complex.

Diana 45 lube pivot bolt
Lube the pivot bolt with moly and slide it through the pivot bushing.

Screw the pivot nut onto the end of the pivot bolt and tighten the bolt. When the barrel stays in any place in its arc, the pivot bolt is tight enough.

Diana 45  install pivot bolt nut
Screw the pivot bolt nut onto the pivot bolt threads. Now, tighten the bolt until the barrel stays where it’s put.

Install the trigger
The barreled action is now put into the mainspring compressor, and the compressor is adjusted to center the action. That way the trigger group can be pushed straight into the spring tube.

Diana 45 in compressor 1
The barreled action is installed in the mainspring compressor.

Two things align the barreled action in this mainspring compressor. First — the barrel presses against an aluminum bar that has a raised spot in its center. The raised spot enters the crown at the muzzle of the barrel and holds the gun centered when it’s under spring tension.

The other alignment feature is what I call a bridge. On this compressor, the bridge is a set of 4 bolts whose tips are adjusted to hold the spring tube in perfect alignment with the screw ram of the compressor. That way, the thrust force on the trigger group is aligned with the spring tube, and the parts go together straight. I use a heavy piece of leather to protect the finish of the spring tube.

Diana 45 in compressor 2
A thick leather belt section protects the spring tube from scratches made by the ends of the centering bolts.

The final step is to install the trigger group. When this is done, pay attention the the flat on the base of the spring guide. It aligns with the bottom of the trigger group and keeps the guide in place. If you don’t align it, the gun won’t go together. Another “ship-in-a bottle” maneuver!

Diana 45  align spring guide
This flat on the rear spring guide must be aligned with the flat surface of the trigger group.

Diana 45 in compressor 3
The trigger group with safety bar is installed in the compressor. I use a lead block in the compressor to keep from marring the plastic of these parts — mainly the safety bar.

Now, the compressor screw is wound and the trigger group enters the spring tube. The goal is to align the two crosspin holes that we saw in disassembly. Use a strong flashlight to confirm alignment of the holes, then press the rear pin through its hole first. There’s a leaf spring inside the safety bar, and this pin opens that spring for the front pin to slide in.

When I say “press” or “slide,” I really mean to tap the pin with a plastic hammer. These pins do go in easily, but the spring tension inside the safety bar takes a little forcing to get them through. This is yet another “ship-in-a-bottle” maneuver.

Diana 45 hole through trigger
These 2 crosspins in the spring tube have to be knocked back through the spring tube and trigger. Put the rear pin in first to open the spring for the front pin.

Install the barreled action in the stock
The last pin that goes through the trigger assembly hasn’t been put back yet. First, drop the barreled action into the stock and press it down until the hole through the side trigger assembly aligns with the holes through the stock. It helps to align things with a slave pin or a pin punch. When the holes are aligned, drift the last pin through the side of the stock.

Diana 45 crosspin coming out
The crosspin that holds the barreled action in the stock is drifted back through the trigger group and stock.

Finally, tighten both forearm screws and the job is finished. Or, is it?

Quick function test
I can’t tell you how many times I’ve reached this point, only to discover that the gun would not cock for some reason. Maybe the new mainspring was coil-bound (too long when fully compressed to allow the sear to catch the piston), or maybe one of those several “ship-in-a-bottle” maneuvers was done wrong. Whatever the case, you aren’t finished until the rifle can be cocked and fired without incident.

I did cock the gun and everything seemed fine. Then, I fired it, and it did shoot as it should. There were 3 detonations at the beginning, then about 25 shots that dieseled to the extent that I could smell the burning oil. After that, the rifle settled down and acted like it had before the tune — except it is noticeably smoother.

I would like to tell you that this rifle no longer vibrates when it fires. That was the goal of this tune. But alas, it still does vibrate. The amount of vibration is about half what it was before the tune. And it has been going down since I started shooting. It was at 75 percent in the beginning. I have hopes that it will continue to smooth out as it breaks in, but I doubt it will ever be entirely free from vibration. As of now, I’m attributing that to the leather piston seal. I think this design has passed the point at which a leather piston seal is able to function smoothly. Or, perhaps, the Diana 45 is a design that cannot be made perfectly smooth.

In the next report, I’ll chronograph the rifle so we can compare it to what it was doing before the tune. I didn’t want more power, but I do want to know where the gun is at this point. This is where I’ll end things today.

One last thing. I hope this report has convinced you to NOT take apart your Diana 45! That was the purpose of all my “ship-in-a-bottle” remarks. This is a complex spring piston rifle that would not be ideal to learn on. But if you must do it, I hope I’ve shown you all the tricks to the job.