Low Power follow up for Impact MK11 with PP,700mm, .25cal

A short recap of my original post: Using the JSB 34gr pellets I was only able to get 920fps with the reg. set at 115-120bar. Adding more reg. pressure did nothing. The hammer spring was changed to the 57mm, 52mm is what comes with the power plenum version, and was maxed.

Here's what I did: With the gun completely stock the valve spring was changed to a lighter spring. A few springs were tried before the one pictured was finally used. The stock valve spring on the left is .040-.041'' wire size with an OD of .280'' and a solid length of .950''. The spring on the right has a wire size of .020'', OD is .260'', and a solid length of .25''. By making the valve spring lite it therefore took less hammer to open the valve. It also would stay open longer. The black delrin piece is .25'' with an OD of .280''. This was put in as a stop in the valve cap at the end of the reveiver so the valve rod would not be able to open so far as to come out of the valve housing at the breech end. By making it .25'' in length the valve adjusting knob at the end of the receiver could be put on the 4th line. With this setting the valve had a max opening of .150'' which was found to be all that was needed. You can open the valve .200'' without risking the other end from coming out of the housing but t he difference from .150'' and .200'' yielded no increase in velocity. The velocity gain from doing this and nothing else was 40 fps. 

The 2nd and last thing that was done was open the transfer port and match the probe. The stock port is a .203'' round circle. My port measures .216'' wide and .260'' long. That is on the conservative side. If it's made too large the pellet/slug will hang up and jam. This step needed to be done slowly and carefully. Also care needs to be taken to clean any burrs on the inside of the port. If you ruin it another one can be purchased from FX for $29. Best to go slow. This mod. netted another 40 fps. for a total of 80 fps with just these two mods. I found that trying to find different springs was almost impossible. It would be easier to get a round ticket to the moon, so I made mine. Music wire can be purchased with different gage wire. I had different wire sizes that were used to make lighter trigger springs for my revolvers. My settings for the above velocity are as follows: reg. was just under 135bar, hammer maxed and valve opening .100''. Note that the valve was only opened .100'' to get that velocity. When it was opened .150'' there was no increase in velocity. When shooting some slugs more velocity was obtained by opening the valve .150''. But not much. Only 7 fps. That's where the tuning comes in. Also, I put some tape on the valve knob and marked the tape to tell me how much the valve would open. This made it easy to repeat settings for different projectiles. Same principle as putting tags on ones scope turrets for different ranges. Hopefully this info will help some of you. These mods cost just about nothing in dollars and cents. It does take some time. The power's there but with some guns it has to be extracted to get it.