Short Stroked my TX200

[Sqwirl57]

Several moths back I had purchased a longer piston rod for my TX with the intent of shortening the stroke some. Today I finally decided to undertake the project and boy howdy am I glad I did. Shot cycle is a bit smoother and I greatly appreciate the new cocking stroke. I was never a huge fan of the *click* *click* *click* so the new single click anti-bear trap is much more appealing to me. The new piston rod is 11mm longer so I BELIEVE that I am closer to an 80mm stroke vs the old 90+ millimeter stroke.

I went through a few springs and setups to get where I am now and ended with a full length 12fpe PG4 kit (was 11.8fpe prior to work) with 3x washers installed to add 3/8" or so of preload. This is putting me at around 10.3fpe at the muzzle using 4.53 JSB 8.44gr. Without washers I was closer to 7.5fpe.

My question to you guys who have done this before, is there a better spring option? Should I open up the transfer port some? I would rather lose the washers to cut down on some piston weight here while still maintaining a nice shot cycle in the 10.5-11.8fpe range. Any advice is appreciated. Thank you!

10x at 30m, ~7mph wind

Chrono data for those curious:

 

[Michigander]

If you plan to stick with the PG4 kit you will have to use a spring with the same OD and wire diameter to maintain the proper fit to the guides. You can add coils or spacers or both. My short stroke setup with a PG3 kit used a 31 coil spring and a 0.300" delrin spacer for a muzzle energy of 11.8 ft-lb. Preload ended up at 1.945". The same setup without the spacer gave a muzzle energy of 10.8 ft-lb. The PG3 spring has a 0.113" wire diameter and 0.730 OD.

 

[Sqwirl57]

If you plan to stick with the PG4 kit you will have to use a spring with the same OD and wire diameter to maintain the proper fit to the guides. You can add coils or spacers or both. My short stroke setup with a PG3 kit used a 31 coil spring and a 0.300" delrin spacer for a muzzle energy of 11.8 ft-lb. Preload ended up at 1.945". The same setup without the spacer gave a muzzle energy of 10.8 ft-lb. The PG3 spring has a 0.113" wire diameter and 0.730 OD.

Thats actually what I was thinking. I may just order a new PG4 spring with an extra couple of coils to eliminate the need for spacers. I would be very happy at 10.8fpe. Thanks for the insight!

 

[Mycapt65]

The longer spring is a good idea. Opening the transfer port is a bad idea. You'll increase "lost volume " and your velocity will drop.

As far as spacers go they have to be experimented with. Spacers can be made from light materials like delrin or nylon or heavier steel washers. Sometimes more weight atop the spring increases momentum and reduces piston bounce. This can help particularly with heavier pellets. On the other hand adding weight atop the spring can slow the piston down in comparison to the same sized spacer made of delrin.

Sometimes the lighter spacers work better than steel spacers because they reduce moving mass and the piston accelerates quicker. Sometimes that can create more piston bounce and efficiency suffers. IMO because of the infinite variables the only way to know which way to go is to experiment.

Your other option is have Tom at Vortek make you a spacer that fits under the trigger end of the spring. That will shim your spring without changing moving mass.

Good luck with your project and don't touch the transfer port.

 

[Sqwirl57]

The longer spring is a good idea. Opening the transfer port is a bad idea. You'll increase "lost volume " and your velocity will drop.

As far as spacers go they have to be experimented with. Spacers can be made from light materials like delrin or nylon or heavier steel washers. Sometimes more weight atop the spring increases momentum and reduces piston bounce. This can help particularly with heavier pellets. On the other hand adding weight atop the spring can slow the piston down in comparison to the same sized spacer made of delrin.

Sometimes the lighter spacers work better than steel spacers because they reduce moving mass and the piston accelerates quicker. Sometimes that can create more piston bounce and efficiency suffers. IMO because of the infinite variables the only way to know which way to go is to experiment.

Your other option is have Tom at Vortek make you a spacer that fits under the trigger end of the spring. That will shim your spring without changing moving mass.

Good luck with your project and don't touch the transfer port.

I have a lathe that I haven't plugged in yet. I could make my own trigger side spacer! Thank you for the idea and I will NOT touch my transfer port haha.

 

[Michigander]

My spacer was on the rear of the spring to avoid adding mass to the piston, although a delrin spacer doesn't add much mass anyway.

 

[Sqwirl57]

My spacer was on the rear of the spring to avoid adding mass to the piston, although a delrin spacer doesn't add much mass anyway.

My three spacers are definitely on the heavier side. I've gone ahead and ordered a new, longer spring for my PG4. I'll add a coil and then turn myself a spacer to fit into the rear of the spring if needed and go from there. Appreciate the advice!

 

[Michigander]

I added three coils going from standard to short stroke in order to maintain about the same energy. You can always shorten the spring if you overshoot.