TX200 Mark III
The TX200-MkIII is a legendary underlever spring-piston air rifle.

Part 1

This report covers:

  • Where were we?
  • Seal was shot
  • How to fit the new seal
  • Most difficult job
  • What did BB do?
  • Assembly
  • End cap
  • Cocking effort
  • Trigger pull
  • Summary

Readers, I wish you all a very Merry Christmas. I am taking off tomorrow as my Christmas holiday, so this report will be up until Monday, December 27.

Today we revisit the TX200 Mark III for the completion of the tuneup. Listen up, TX owners. You’ll learn some things today.

Where were we?

In Part 1 I showed you the TX teardown and why it is one of the easiest spring piston guns to tune because a mainspring compressor isn’t required. I also showed you a mainspring that had been coated with black tar grease, which is the airgunner’s name for the open gear lubricant that’s used on exposed gears like those found on drawbridges.

But the biggest problem was the cracked piston seal. Several readers offered possible explanations for this. I think it was the black tar. Some of it liquified and went everywhere inside the powerplant.

The presence of black tar told me that it’s been a long time since I was inside this powerplant. I haven’t used black tar for a tune job in I can’t remember how long.

Seal was shot

What you didn’t get to see was when I removed the piston seal it crumbled into many pieces. It was completely petrified! Even without the crack I showed you it wasn’t working. So this report came along at the right time.

I ordered a new TX seal from Pyramyd Air. It arrived about one week later, and I set aside time to replace it and clean and lubricate the powerplant.

TX200 piston seal
The new TX200 piston seal.

The seal goes on the end of the piston, where it has to fit over a mushroomed steel piston head. Naturally the hole through the piston seal is smaller than the mushroomed end of the piston that it has to fit over. And when you receive it the seal isn’t very pliable. What do you do?

TX200 piston head
The new seal has to fit over the wide end of the mushroom on the piston head.

How to fit the new seal

No doubt there are several methods to do this. I will give you mine. First the seal has to be made more flexible than when it comes from the package. How you do this is up to you but I don’t recommend microwave ovens. A hot water soak would be fine, and maybe a heat gun is going too far.

What I do is flex the seal between my fingers until it loosens up. Another way is to make a tool that allows the hole in the seal to expand gradually and then slip onto the piston head. Let me show you with a .50 caliber BMG bullet.

TX200 seal bullet
A tool that’s shaped like this .50-caliber Browning Machine Gun bullet (minus the boattail) will work, as long as the base of the tool is just as wide as the top of the mushroom on the piston head. This bullet is too small but you get the idea.

Stand the base of the tool on the head of the piston and then slide the new seal down the tool and onto the piston head. The hole in the seal will expand gradually and slip right onto the piston head. For the airgunsmith who will do many such replacements, I recommend making such a tool. But for you TX owners who might replace a seal once in your life, I would just flex the seal in your fingers until you can almost “button” it over the mushroom. I then use a screwdriver to pry it over the lip of the mushroom. This stretches the seal, making it more flexible.  Sometimes I just press forward on the piston with the new seal in place, then I slowly twist the piston. That usually gets the lip of the seal started and then the pressure forces it onto the piston head.

TX200 seal on
Yes it’s difficult and takes time, but the new seal will go on the piston head.

Most difficult job

Replacing the seal in a TX200 is the most difficult job in the entire overhaul. Besides that, everything is easy. But I had some cleaning to do and that took a while.

Build a Custom Airgun

What did BB do?

All of you discussed how I would clean that black tar off the mainspring. Well, I’m going to tell you, but first let me tell you there was a lot more to clean than just that. The inside of the piston where the mainspring lived for more than a decade needed cleaning, as did the last several inches of the spring tube where the end cap lives.

First the mainspring. I used a can of carburetor cleaner. That’s the stuff that comes in a gallon pail with a wire parts basket inside. I know there are spray cans of this stuff and they are probably handier for a job like this, but I used what I had on hand. I use this pail to clean my legal .22 rimfire silencer after shooting several hundred rounds through it.

This removed about 80 percent of the tar, but not all. Then I threaded a paper towel through the coils and wound the spring so the towel got the entire length of the spring — inside and out. That got me to 90 percent clean.

Then I settled down with cotton swabs and a small screwdriver. Some of the tar had hardened on the spring. It had to be scraped off.

The TX200 mainspring has been shot-peened which gives it a rough surface that holds grease quite well. The shot-peening is to remove stress, but the surface it leaves behind has its uses, too.

For the inside of the piston I used more paper towel on the end of the thin-bladed screwdriver and now I was using Butch’s Bore Shine rifle cleaner that is so solvent that it comes with warnings about touching it. In all it took me over an hour to clean out all the tar, and this is the last time I will ever use it in a spring gun. Now that Tune in a Tube exists, why would I ever mess with anything else? For those in other countries, Tune in a Tube is Almagard 3752 red grease, and there are a number of other red greases that are made from the same stuff.


To get the piston seal into the sliding compression chamber I slid the chamber all the way to the rear by pulling the underlever down and then I had to turn the piston many times before it “buttoned” itself into the chamber. While we are on the subject of the piston, let me share something with you.

The rear of the TX200 piston doesn’t fit into the compression chamber. It slides inside the spring tube, where its bearing keeps it centered on the compression chamber. This is one example of the fine engineering that went into this air rifle. I used moly grease on this bearing and the inside of the tube and it is still in place more than a decade later.

TX200 piston
As you can see, the rear of the piston (on the right) is larger than the rest of the piston. It slides inside the spring tube, keeping the piston centered in the compression chamber.

Once the piston is in the rifle the rest of the assembly is quick and easy. Press the ratchet to release the underlever with the compression chamber and the piston and chamber slide all the way into the powerplant. Spread a thin coat of TIAT on the mainspring and slide it into the rifle. While it was still outside the gun I checked and both ends felt tight on the spring guide. That addresses vibration to a certain extent. The TIAT takes care of the rest.

End cap

The last task in assembling the powerplant is to put the end cap into the rifle. This is the reverse of how we took it out. Simply slide the cap into the spring tube, then stand the tube upright and press down on the tube to align the one bolt hole for the one bolt that you can turn with your fingers. It has 10mm flats if you want to go that way or a Crescent wrench for the rest of you.

TX200 end cap
The end cap is pressed in until the two holes align. Notice, too, that the mainspring isn’t heavily covered with grease.

Once the powerplant is together the barreled action goes back into the stock. Now the rifle is ready for testing. I cocked and shot it several times to ensure that it was calm and functioning normally. But it’s the chronograph that will tell the whole story. Remember in Part 1 when I ran a baseline velocity test I saw 7.9-grain Crosman Premiers leaving the muzzle at between 786 and 881 f.p.s. That wasn’t the rifle I remembered. How is it now?

Now the TX200 Mark III averages 929 f.p.s. with an 11 f.p.s. spread, from 922 to 933 f.p.s. Apparently that is the way this rifle wants to behave with Tune in a Tube on its mainspring. Did the new seal work? I should say so! My experience with TXs tells me the rifle will speed up as the tune break in.

Cocking effort

The cocking effort is 36 lbs. That’s one pound lighter than the HW 50S and the TX develops more power (15.14 with this pellet).

Trigger pull

Stage one pulls with 4.8 ounces. Stage two breaks at 9.7 ounces. Not going to do anything to this trigger!

You can safely set the trigger lighter on a TX than a Rekord because of how the unit is designed. Yes, it was designed after the Rekord but it isn’t an exact copy. I’m going to leave this one as it is.


We are now back on track with the TX 200. The next thing will be to test its accuracy. And that beautiful new Meopta Optika5 4-20X40 will get the honors. Stay tuned!