HW 50S
The HW 50S breakbarrel from Weihrauch.

Part 1
Part 2
Part 3
Part 4

This report covers:

  • Vortek PG4 Steel 
  • Rekord
  • The old parts
  • Nailed together
  • Clean the powerplant
  • Install the new piston seal
  • Grease the new mainspring
  • Assemble the barrel
  • End cap
  • Four tabs in
  • Install the trigger
  • Into the stock
  • Summary

Happy day after Thanksgiving. About two decades ago this day was called Black Friday, because it was supposed to be the day when retail outlets in the U.S. turned a profit for the first time that year. This year Black Friday started in September and now the marketers are looking for new adjectives to describe their sales. It seems when you use the word “amazing” all the time it loses some of its meaning.

Today I am going to install the Vortek tuneup kit for the HW 50S air rifle and see where it takes us. I have a lot to tell you so let’s get started.

Vortek PG4 Steel 

All along I have been telling you that what I’m installing is a Vortek PG3 SHO kit, but it really isn’t. It’s a Vortek ProGuide4 Steel HO kit with Quad (4X) Guide Design. Pyramyd Air doesn’t stock this kit yet, so I called Vortek and talked to Tom Gore about it. He told me it was an amazing kit (there’s that word again), which I expected him to say, but Tom’s kit for the HW 30S turned out quite well, so I had high hopes for this one. The HO in the name stands for high output, so this one can go as high as 12 foot-pounds. In part 2 we learned that the factory rifle was already putting out around 11+ foot-pounds, so the increase isn’t that much and I didn’t want it to be. What I was after was a smooth shooter.


The first step was to clean and lubricate the Rekord trigger. I just used cotton swabs for this; I didn’t get crazy. After that I lubed the sear with moly grease. Then I tested the trigger.

Outside the rifle the stage two trigger pull seemed too heavy, so I lightened it with the big screw behind the trigger blade. Cocking and testing the trigger also gave the moly a chance to work into both sear surfaces. I must have cocked and fired the trigger 15-20 times as I adjusted the screw. When I finished the trigger was breaking much lighter than before. I will test it again when I test the velocity.

The old parts

On Wednesday you read about the removal of the old powerplant parts. Out of everything that was removed I will just use the piston with the new tune,

HW 50S PG4 old parts
Of all these parts only the piston will be reused.

HW 50S PG4
Everything but the piston comes in the kit. The new piston seal is not shown.

HW 50S PG4 springs
Just the factory spring by itself (bottom) is longer than the PG4 spring with its guide (right) and top hat.

No only is the PG4 spring shorter, it’s made from slightly thinner wire. It measures 0.119-inches in diameter, while the factory spring wire measures 0.122-inches.

Nailed together

I tried to remove the PG4 mainspring from the steel spring guide and noticed that it is nailed on. No amount of twisting could take those parts apart. There will be no vibration from loose tolerances in this tune!

Build a Custom Airgun

Clean the powerplant

I looked into the spring tube with a strong light and there was next to no grease inside, so there was nothing to clean. Normally I would clean the inside, but this one was clean and dry.

Install the new piston seal

I snapped the new piston seal on the end of the piston. It seemed smaller than the factory seal, so I assume the parachute will expand rapidly to seal the compression chamber. We shall see.

HW 50S PG4 new seal
The new piston seal is the same size as the piston. It’s smaller than the factory seal.

The synthetic top hat of the new kit has three notches for the end of the mainspring to rest in. This determines how much preload the mainspring has. It came with the end in the lowest notch which is the least preload, and I left it there.

HW 50S PG4 preload
Three notches of different heights determine how much preload the mainspring is under. This notch is the lowest and softest.

Grease the new mainspring

In preparation for installation I applied a thin coat of the grease that came in the kit to the mainspring and piston seal, plus the rear of the piston body.

Assemble the barrel

Now the barrel goes back on the spring tube so the cocking link can be connected to the piston. Of all the steps in assembly, this one is the trickiest because many things have to happen at the same time. First the cocking end of the link that’s connected to the piston is lubed with moly grease. Then the link is is slid through the spring-loaded bridge on the underside of the spring tube, and that’s when I noticed something new. Weihrauch now puts a long synthetic bearing on the bottom of the link so it will slide over the spring tube smoothly. I hit that bearing with some moly, too.

HW 50S PG4 link bearing
The long synthetic bearing on the bottom of the cocking link (bottom of this picture) gets a coat of moly grease.

Now slide the piston into the spring tube. You will find that with the new piston seal it slides in without any resistance.

Once the cocking link is connected to the piston the barrel can go on the spring tube. There are two thin pivot washers, one on either side of the base block, and they must be lubed with moly and aligned so the pivot bolt will pass through. Aligning them used to be a problem for me until I learned to stick them down with grease. They are so thin you can push them into the gap between the base block and the action forks.

HW 50S PG4 pivot washer
To hold that pivot washer (arrow) in place, coat both sides of the washer with moly grease. The washer then slides between the action fork and the base block as you align the pivot hole. It doesn’t have to line up perfectly.

HW 50S PG4 pivot hole alignment
Just get the pivot washer aligned this close and you can stick a small Allen wrench through all the holes to align things perfectly. Once that is done the pivot bolt will slide right in the hole.

If this sounds complicated, that’s because it is, more or less. It takes some experience to get it to work right because you are trying to hold the base block in alignment with the hole in the action forks. And here is a tip — just worry about the left side of the spring tube for now. Get the pivot holes lined up, then slide the pivot washer in far enough in that you can get a small Allen wrench through to fully align it — see the picture.  Then slide the pivot bolt in the hole and it will hold everything in place as you turn the spring tube over to work on the right side. But watch that pivot bolt, because it wants to slide back out of the hole!

HW 50S PG4 pivot hole alignment 2
Once the pivot bolt is through the left side of the gun, position the bolt tip (arrow) just below the hole on the right side, then push that side’s greased pivot washer into position and run the bolt through. The grease on the pivot washers allows them to slide sideways with ease.

Grease on both washers is the answer to many things. It holds them in place and also allows them to slide when you need them to.

End cap

Now the spring and guides, the rest of the PG4 kit, can be slid into the spring tube, because the next step will be to put the end cap back. Fortunately, putting the cap back is much easier than removing it the first time. However, there is something to watch for.

The end cap has a bushing that contains the threads for the front trigger guard screw — the long one. This bushing slid out of my end cap during disassembly. Make sure it is back in place before you install the end cap or that screw will have nothing to thread into.

HW 50S PG4 end cap bushing
Make sure this threaded bushing is back in the end cap before you install it.

I put the barreled action back into the mainspring compressor and when I slide the end cap in I note that the PG4 spring and guides are a little less than a half inch shorter than the factory spring and guide.

HW 50S PG4 end cap fit
With the mainspring compressor still set where the factory spring was fully relaxed, there is now this much more clearance. The PG4 kit is this much shorter.

Use the compressor to slide the end cap into the spring tube, making sure that flange that retains the cap is rotated clear of the spring tube. Otherwise the cap will jam on the flange.

HW 50S PG4 end cap clearance
Rotate the end cap to give the locking flange clearance.

Four tabs in

Once the end cap is locked in place by the flange you can replace the four tabs that were such a bother to remove. They now go in easily. Just position them over their holes and whack them with a rubber mallet. They are identical so it doesn’t matter which hole they came from. One whack seats them flush with the spring tube.

Install the trigger

There is a secret to installing the Rekord trigger. Cock it first. It can be installed uncocked but it will fight you to align the crosspin holes. Cock it and they align easily.

HW 50S PG4 Rekord uncocked
The Rekord is uncocked.

HW 50S PG4 Rekord cocked
Push the rear of the spring hook down and the top of the sear will grab it.

Don’t overlook the safety button when you install the trigger! 

Into the stock

With the barreled action together, install the rifle in the stock. Pull the trigger if it didn’t fire during installation and then cock the rifle. Be prepared to shoot it several times, to let the new parts get used to the rifle.

At this point I note that the rifle has no vibration, but it does have a powerful jolt when fired. I’ll watch that as the test continues.


This work took about 2-1/2-hours, start to finish, but there were a lot of pictures to take and that probably took half the time. I worked slowly and watched to make certain I wasn’t leaving anything out. Been there, done that, got the T-shirt and wore it out.

We are now ready for the next report, which will be a retest of velocity, cocking effort and the trigger pull.