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

TX200 short stroke with Walther LGV piston

TX200 Mk3 with Walther LGV piston…Bring on the short stroke drop in.

We had a long thread about short stroking the TX200 Mk3, the -14mm of the mk1 piston makes the TX quite nice but it requires a new rod or piston cap to reduce the stroke on a mk3 piston as mk1 pistons are no longer available.

So…I dropped a Walther LGV piston into a TX200 mk3 to experiment a little and report what I found.

Now the Walther piston seal is special, its designed to work well with offset transfer ports, you can NOT use this seal in the TX, way to much lost volume.

So..I swapped over to the Vortek piston seal, this had the added benefit of adding 2.5mm to the piston stroke.

So to start the specs of the Walther piston dropped in a TX200 with Vortek Vac25 piston seal.

First off I had Mattyboy measure up a Mk1 TX piston, front face of piston to sear engagement point on cocking rod.

= 165mm

next up I measured up a LGV piston.

LGV piston = 173.5mm

8.5mm difference in stroke

So the LGV piston in TX chassis would give 76.5mm stroke

which gives 37.56CC swept volume

Now my gun has a 4mm transfer port..so TP at 4mmx9mm long 0.1131428CC

Static compression ratio 37.56/0.1131428 = 331:1

Now I have ONLY tested this with the LGV spring and it is to long, I will shortly have a TX200 Mk3 stock spring to test with so I will revisit this, keep in mind the LGV spring is to long so the gun was a little oversprung, the LGV spring did fit the tophat and rear guide well so those wishing to experiment could just shorten the LGV spring if they wish…

FTT 8.8gr (weighed) 10.8FPE
Daystate Li 8gr (weighed) 11.05FPE

I do not have any AA fields, they are efficient in this gun and I would expect them to land around 11.2FPE max , when I revisit this I will have AA fields/Exacts to hand.

Now, I did no reshaping to the sear engagement point on the rod of the piston, it is nearer to 90deg where the TX is slightly set back a little more, the rod could be reshaped and polished to match the TX rod as it is hardened all the way thru…me, i would not bother.

So to make it clear, the LGV piston is a drop in replacement for the TX200 piston to short stroke using the Vortek Vac25 piston seal to 76.5mm stroke

bear trap…right now mine here is disconnected, I doubt it would work correctly as I had issues with when i tested -18mm stroke and we are now at -22mm or so. When I revisit I will add it back and retest.

Those wishing to experiment, you could machine the piston head back a tad, machine up a bronze or alu piston head and sit a 21mm ID 2mm CS O ring up front and push the stroke to around 78mm, at 76.5mm it is making 11FPE, keep this in mind.

I measured up the bare TX200 mk3 piston at 227g and the LGV piston at 252g

  • Ah! An excellent write-up.
    Please share a drawing to us, we can make product based on your input.
    ———————-
    http://target-tune.in
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  • Easier just to buy a Walther piston 😉

  • Hi Tony

    First of all thank’s for the many informative post’s you have put on here and the forums.

    I have a hW95 26mm version that I have tuned to be very smooth at 11 ftlbs. I would like to improve smoothness further still. Your posts indicate a comp. ratio of 300
    being optimal. After some thought I came up with the idea I could insert an intermal spacer in the comp. tube and then carry the tp through into the cylinder. This could balance out the comp. ratio by giving more tp. vol. and less stroke. Your thought’s would be greatly appreciated.

    Regards Steve G

  • Did the Vacseal just fit right on the Walther piston? Or did you have to modify it?

  • straight on, no mod needed 😉

  • What is the rifle like to shoot now?

  • The air arms piston is back in now, (its still short stroked by 14mm) The article was more to show you what can be done.

    The rifle was very quick, the conversion is probably more suited to .22 over .177 although if you added 3mm to the length of the piston rod it would be perfect for .177

  • Hi Tony,

    It’s great to read about your experiments with short stroke piston alternatives with the TX. Thanks!

    Would you think a MKI V-mach spring kit (if obtainable – Blackpool is currently out of stock…) would work with the LGV piston, or would you suggest another spring? I’ll be eager to hear how you think a TX MK3 factory spring works.

  • The V-Mach spring would be a good option as its short and slightly fatter wire, alternatively measure the spring you have and see if you can get something a little thicker that will fit in the piston(21.5mmOD) and fit on your spring guide.

    The Titan no7 may be a good choice although you may have to set it to length

  • Tony, do you think a V-Mach seal for a 25mm HW77 would fit the LGV piston? Since the Vacseal-25 is made for that gun I thought it might but didn’t know if there were clearances involved. It would be nice to try various seals if they all conformed to the same mounting solution.

  • V-mach seal will fit the LGV piston no problem, that is the HW77 25mm V-Mach seal 😉

  • LGV piston is ordered from Germany – it’s on the slow boat. I was going to order a V-Mach 25mm seal but someone posted about cocking issues…hmm. Will order Vacseal-25 as well.

    Tony forgive me but I’m trying to understand optimal compression ratio. I have calipers and should be able to measure my transfer port. In a nutshell is your premise that these guns can shoot far faster and more efficiently if they sweep less volume? In effect a stock Mk3 TX200 is shooting as 12fpe mainly because of a lazy spring? Then by adding something with the short stroke such as +14mm rod or a LGV piston (even shorter) and a stronger spring you can make the same power with far less swept volume? My understanding is that the compression ratio is what you are trying to tune to control shot cycle/piston bounce? I would have figured that you’d need to make the transfer port smaller but perhaps the transfer port is actually too large in a standard Mk3 and is more optimal for these shorter strokes? Sorry for the book 🙂 Can’t wait to try this out. My Mk2 is a Maccari with 10 bear trap notches so it will still work even with the short stroke conversion. Great work – really enjoy the blog!

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