Quote Originally Posted by cooper_dan View Post
Its hard to go back to standard, and I guess I didn't properly explain my reasoning. There are 2 main points:

1- Why did I change the breech seal?
My favourite pellets in this gun are by a clear margin, die 54 JSB exact. I'm talking 12mm groups (10 shots) at 45 yards. They are basically magic in this barrel. However die 54 have a slightly longer skirt than other dies, so they ever so slightly stick out of the barrel (just a fraction)
With the standard o-ring seals, they compress when firing and allow the compression tube face to touch the face of the barrel. Unfortunately this means that fraction of pellet sticking out gets clipped off and leaves lead swarfe behind. This then gets behind the seals/round the comp tube etc and is just a mess.
The one piece Weihrauch seal I've put in there is harder than the o-rings, so the compression tube is always held slightly away from the barrel. I've put about 200 shots through with this new seal and not had any clipping or lead swarfe. So one problem solved.

2 - Why mess with the static compression ratio
Unfortunately the fix above came with the downside of a harsher shot cycle, which to me feels 'slammy' (although I could be dead wrong about this, I just know there was a definite change and I don't like it). I think because I no longer have the squishy o-rings in there to soak up some of the perceived force.
My TX has been short stroked to 80mm. So with the 25mm diameter piston and new breech seal, should be almost identical to an old Weihrauch HW77 or HW97. However its a lot harsher (side by side comparison).
Looking through the rifles, the clear difference to me is that the Weihrauchs have a much shorter and smaller diameter transfer port, and a flat faced piston seal.
Looking at the static compression ratios (simplified calculations), the Weihrauch is approaching 1000:1. My TX200 (including the lost volume in the seal is nearer 200:1. By filling in the seal volume, it rises to 400:1, therefore should get me a bit closer to the HW77/97 numbers.

Basically I'm trying to make small adjustments so that I can keep using these pellets.
I know you know what you're doing, Dan. And that you can certainly shoot and you know what you want from the gun. But I think I'd be tempted to increase the stroke slightly, if do-able. Maybe 5mm. And let this slightly larger volume work slightly less hard than the reduced volume. There'd be hardly any difference in piston time. If by later fitting the parachute seal the efficiency was increased, you could then go even lighter on the spring?