AirGunTech: Re Engineering Spring Powered Air Rifles for smoothness, consistency, and to better suit UK power levels.

TX200 Mk3 quick short stroke conversion to conver the mk3 to the same stroke of the mk1

Air Arms originally designed the TX200 to very closely copy the bore / stroke / swept volume of the early 25mm piston HW77’s, then in a move i can only think was sales driven (USA market) they decided to up the power capability of the TX. This meant for UK use the guns were set up with a softer spring and heavy piston weight/tophat..not idea at all!!

I’m not going to go into mega detail on this conversion, I swapped a sweet HW98 for a TX200 purely to experiment and see if I could get the TX as nice as the HW97…and i believe i have managed it. To start I short stroked the TX down to 39CC with -18mm stroke using a new alu piston nose (so same as the 25mm piston 77’s)…this worked great except the bear trap often would not engage correctly. With this and being short on time i decided to push the stroke to -14mm for just a midges over 41CC swept volume. I may in the future remove the bear trap and push the stroke back again to 39CC (81mm so -18mm) but for now this worked quite well.

Pics show the alu piston nose, i ended up using a Vortek 25mm HW77 piston seal. Initially the conversion used an O ring, the problem i found was it just felt to fast, which sounds very strange…moving to the HW77 25mm seal and noting the seal is cupped so in reality the stroke was increased by 1mm or so it felt much nicer to shoot.





















Piston nose is attached with the 3 grub screws and loctite, it is removable if needed.

For UK sub12FPE use you can copy what I did here or find a mk1/2 piston which has 14mm less stroke..OR fit a new piston rod with +14mm length, i went the piston nose route as its much easier. This transformed a sluggish shot cycle to something very similar to that of the HW97…maybe a tad quicker. You think your mk3 shoots nice? I bet you would say its nicer once this conversion is done, especially if you have ever shot a nicely tuned HW77 or 97.





  • Tony, nice blog! What spring setup worked well with the short-stroked TX? I have one that’s been shortened 14mm (via longer latch rod) and has O-ring piston as well. Current spring/guide is some Maccari spring – about 30 coils, .128 coil size. Some more expert shooters who tried it felt same power (11.5fpe) could be accomplished with a less stiff spring. They recommended V-Mach. Any advice appreciated!

  • the spring in this gun was a V-Mach unit, the one he sells for the mk3 UK spec gun. I however feel a standard AA supplied UK spring may be better as its softer and longer, that way more bounce/surge would be eliminated.

  • Thanks Tony – good info. My rifle currently has aftermarket guides and spring (the guide is so tight I can’t get it off) so perhaps I’ll order a factory spring setup and see how it goes.

  • just have the guide machined down a few thous, if its that tight it will be sapping power….plus it may save buying a spring

  • Tony, do you sell this part at all? I’d be interested to try it out in my TX, since I’ve not been able to purchase an earlier Mark or try a long-rod piston.


  • if you have a digital vernier and can do me some measuring I will make you one…where are you?

  • Thanks, Tony! I do have calipers, and measurements. Should we continue this via email? I’m at mattbrack (at) – and I’m in the northeastern U.S.

  • its going to cost on shipping…have you tried talking to Ed Canoles, he posts on the 54 forums a lot, especially Dianawerk forum and the Yellow forum, he is more local to you and could make a piston head that suited the Vortek seal or make you an O ring sealed head…he has done them for the TX before.

    It may be easier with him being in the USA over me in the UK

  • Yeah, I’ve been coming around to the same conclusion, Tony. Thanks for your honesty – and your ingenuity! I’ll look up Ed.


  • I like the look of your short-stroke conversion! I shall have a go at this but will try and use the standard piston seal. Very interested in the ‘O’-ring system too. Great blog, thanks!

  • Hi Tony. Great blog! I bought a TX200 MK3 last year and it was initially shooting quite well (I’m new to the sport so I have a lot to learn about hold sensitivity and continuity). Recently the groups have been opening up a bit so I plan to do a strip, polish and relube to see if it makes a difference. I may also clean the barrel as the rifle is second hand and I have no idea when it was last done (I’ll only do this if the accuracy doesnt improve with the re-build).

    I am very intrigued by the idea of shortening the stroke as it sounds like it will help with accuracy and recoil. Would you be able to make one of these for me (I’d pay you ofcourse) or at advise me on how I might go about it? I have no real technical or engineering skills so it’s a little daunting.

    I really want to make this rifle a keeper and something that can be passed on down through the family.

    Many thanks,


  • Tony

    Hi, just recently purchased a TX 200 HC and I have just fitted a new venom kit, one thing that was a surprise was previous owner had modified the piston head to take a HW C form seal from a 77.

    I would be interested in the short stroking piston nose if you are making them for resale. It is a very ingenious modification, year ago I owned a MK1 and I used to love that rifle, however over teh year I lost track of it. If you could let me know if you are in a possition to make and sell this item I would be very interest. I take it that no further modifications are required when using this. Regards Nigel

  • I should actually read what I type when using mobile phone to comment on forums as the predictive text and my typo’s make it sound like I am an idiot typing whilst in a spin dryer. Nigel

  • Nigel…all you need is a longer rod on the piston…amy machine shop could do that for you

  • Hi tell me is there a slide conversion to upgrade the tx200mk3 that is a plastics insert Steve, due to your disability’s will it makes the mk3 easier to Oadby?
    Your’s James prentice

  • Due to my disabilities I wish to add the nylon fittings to my tx200mk3 will this make the loading easier for me as I have limited dexterity

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