Short stroke drop in piston for the TX mk3?

[lensman57]

Put one of the TX-pistons in the lathe, and trimmed off a bit of the tube body, and some of the rear bearing/skirt. Combined with the aluminium front, I am now at 208grams wthout seal or tophat. The stroke is at 85mm, with the rod screwed out a few turns.

With a delrin tophat and a delrin spacer giving about 8mm more preload, The gun is right at 10,5fpe with 7,9grs exacts. Shotcycle is quick, less recoil than before, an no slammy feel. Success so far!

Need to prove it on paper...

You can have all this by just using a dropping in kit. But I do understand the urge to constantly fiddle with a spring air rifle to achieve that holy grail of tuning, making a spring rifle behave like a PCP.

A.G

[Shed tuner]

Looks good, but you shoudl be able to add a little preload to increase power slightly and also to balance it...

[FPoole]

Evert, the 85 mm is very close to the old MarkI pistons which were 84, I think. Using the current FAC factory spring and a little preload should get you right on 12 ft. lbs. To be honest, a little buzz or twang isn't the end of the world for me and I have several MarkI's that are pretty much bone stock. I have an SR and a standard gun with all original inside parts except for the JM blue seal. These are real shooters even though they do have a bit of spring buzz. I don't shoot them much because I like to keep the old springs in them just for nostalgia. I have 1 MarkI that I bought from a friend. He had just put a factory MarkII spring in and it was shooting 8.6 grain FTS pellets at 850 fps. The spring broke after a season of FT and I found my friend had left the thick weight in the piston and added another. I put it back together with the one weight and it settled down to just about 800.

[evert]

Evert, the 85 mm is very close to the old MarkI pistons which were 84, I think. Using the current FAC factory spring and a little preload should get you right on 12 ft. lbs.

Thanks. I dont really like the amount of preload I have had to add to the gun, but it feels nice to fire now.

Do you know the weight of the MK1 piston?

[Shed tuner]

Thanks. I dont really like the amount of preload I have had to add to the gun, but it feels nice to fire now.

Do you know the weight of the MK1 piston?

Around 230g.

Why do you not like preload ? it stops bounce and enhances consistency...

[evert]

Around 230g.

Why do you not like preload ? it stops bounce and enhances consistency...

Dont know.. it just Feels wrong to go from a 12fpe setup to a 10,5fpe setup, with the same spring, and having to increase preload a lot.

[Shed tuner]

Dont know.. it just Feels wrong to go from a 12fpe setup to a 10,5fpe setup, with the same spring, and having to increase preload a lot.

Not at all... being able to increase the preload is one of the benefits of shortening the stroke !