Quote Originally Posted by clarky View Post
Tin ...if you your shortening your barrel but sticking on Co2 5ftlbs aint gonna happen.
Ive done a few and these figures may prove helpful for a .22 specimen only ..
Most dramatic velocity increase comes from a longer barrel, mainly required for when the weather gets cold like now and your gun dropping a full ftlb from a stocker barrel.
You can get 15 to 20 fps by using a fishtank airline gasket of silicone but ive used square section rubber washers to even better effect ....let me know if you want sizes...
If you machine off the probe section which contains porting and replace with a 2mm stainless steel probe 1.5 mm longer than stock, you will get 15 fos from increased flow and better seating of pellet past the transfer port. Tip of new probe is best with a 2 mm radius.
Flat topping the valve can create better flow for again 15 fps....
Chopping your barrel loses roughly 50 fps per 2 inches and increase that for cold condiitions...
Useful info! Power at 5 ft/lb should have read "max" on a hot day! Porting, sealing, probing () will offset some of the loss, but I'm just after a short pistol that goes bang and shoots stuff.

My dinky 120mm derringer produces nearly 40 ft/lb but can't hit bugger all! The 2240 project would be useful if: a) I can legally own it in this country. And b) It has sights that have a noticeable effect on accuracy.