Pushing the envelope . :TX 200

[NickG]

Been tuning the tx among other things for around 7 years in that time tried every piston diameter weight stroke configuration you can think of and settled on 21 mm diameter.
Recently got talking to Tony L & Craig p about the possibility of a lower powered rifle for hft , inspired by Craigs excellent Hw 30.
I attempted a 20 mm comp tube a few years back , but couldn't stop it dieseling, so only got 9 fpe consistently, so thought I would have another go at it applying everything I have learned in the years since.
So started with the old comp tube I had( using the tx breech seal set up ) and knocked up a skirtless piston, using an o ring and the hw 30 spring results were promising, so improved the breech with the arrangement I use in my 21 mm , and changed the o ring to a synthetic piston ring, this made power in the tens with 8.4 , but with light 7.3 made 10.8, Tony and Craig would be happy, but I want it for Ft, So aiming for 11fpe plus. Downside is the skirtless piston rocking gives poor consistency, so inspired decided to go the whole hog !





A few random pictures above , in summary I now have a full piston with a steel skirt, which luckily weighs the same as the skirtless one, I will be using piston ring
Aluminium compression tube with bearings to keep everything concentric, breech arrangement that uses an o ring to seal on the outside of the barrel, and seats the pellet,
I have selected a latch rod from my stash that has a longer button on the end to mini mise lost stroke, and increased the scallop in the under lever , managing an extra 2 mm of stroke that's 100 mm.
So latch rod loctite setting as we speak, will be testing over the weekend.
For those wondering I have used ally comp tubes successfully after hard anodising, but for one tube it's too costly, I have the bearings, and piston ring sized so there will be no metal to metal contact, and will be running it with zero lube.

[NickG]

Ok no pictures ��


https://photos.app.goo.gl/X1urba17EG1fWatv9

[flyingfish]

Sounds interesting Nick. Looking forward to following it's development

[Shed tuner]

so the big circlip is to retain the double o-ring sealed comp tube end plug ?
Interesting design, makes it very easy to change the port configuration.. presumably it's a tight enough fit so it's not going to move around much, but how do you get any pressure on the breech seal without it just pushing the end plug back (fractionally) into the tube ?
or the fact that it fits around the barrel, means that the friction rearwards is sufficiently low that this isn't an issue ?
Looks like a nice low-lost-volume solution.

[Jesim1]

Great work, it's what you guys do in the shed today that we see creeping into the main stream in the future

[rapidresponse1]

sounds good bud

[NickG]

so the big circlip is to retain the double o-ring sealed comp tube end plug ?
Interesting design, makes it very easy to change the port configuration.. presumably it's a tight enough fit so it's not going to move around much, but how do you get any pressure on the breech seal without it just pushing the end plug back (fractionally) into the tube ?
or the fact that it fits around the barrel, means that the friction rearwards is sufficiently low that this isn't an issue ?
Looks like a nice low-lost-volume solution.

Exactly that Jon, big o ring crush on the two large o rings, very light on the breech seal, the comp tube outer front face also bears on the action when locked up . It all works without a spring in 😂,have to see what happens when I shoot it .

[RobF]

Sounds interesting Nick. Will be great to catch up next year

[TonyL]

As per comments on that other thread, Nick, very ingenious and with some very inventive thinking in many areas. Well done.. Firing cycle sounds utterly sublime.. Hopefully the long-term longevity testing all goes to plan and it'll be job done.

And all (again, as we said on Craig's 30 thread) from a nice, simple, self-contained format with easy cocking offering easy serviceability and a most forgiving cycle combined with just enough character to let you know it's a living, breathing springer.

[Shed tuner]

Exactly that Jon, big o ring crush on the two large o rings, very light on the breech seal, the comp tube outer front face also bears on the action when locked up . It all works without a spring in 😂,have to see what happens when I shoot it .

worst case you can always add a couple of grub screws to take out any movement.. interested to see how it all works out

[T 20]

Exactly that Jon, big o ring crush on the two large o rings, very light on the breech seal, the comp tube outer front face also bears on the action when locked up . It all works without a spring in 😂,have to see what happens when I shoot it .

Just a thought Nick.

Would it be worth making you cylinder end plug with a step in it and machining the tube to suit, then the circlip could be used to lock the plug in position ?



All the best Mick

[NickG]

I did it this way Mick so the end plug could move rearwards as the tx barrel isn't always the same length, and the linkeage can differ slightly , it saves me having to be too critical on the depth of the breech recess ,however with this 20 mm I need max stroke , and having it slide shortens the stroke slightly .