Tuning Tuning an FX impact 2 for accuracy while maintaining high pellet energy.

[Oldandintheway]

Gentlemen; I own an airforce 50 cal Texan LSS and it will put five 250 gr bullets in the same hole at 65 yards. I also own an FX Impact 2 that I am getting really frustrated with. It won't come anywhere near the Texan accuracy. I have it tuned so that it will repeat the velocity of 860 FPS and each shot within 5 FPS, when I use carefully weighed pellets. Plenum pressure set at 135 Bar. Rotating ring pressure set at 5 (max). Hammer pin set at just barely touching. It would get about 3 inch groups at 100 yards. Not good.

I moved the hammer spring restrictor in about two full turns. That reduced the pellet velocity to 715 FPS, with a deviation of only 7 FPS., and dramatically increased accuracy. That, however reduces the total energy by a lot (down to about 90 F LB). I'm happy with the accuracy but not with the total energy.

My question for this esteemed group is, Does the velocity of the pellet, regardless of what combination of power from the two power setting possibilities and the location of the hammer spring limiter determine the accuracy of your rifle, or does the exact combination of those three settings derive a good accuracy? I know that that's a little hard to understand, so let me try another way to ask this question. Lets say that you had your plenum pressure set at 135 pounds, and your rotating ring power setting at 3 and your hammer spring limiter set at 4, arriving at a pellet velocity of 850 FPS. You then changed your plenum setting to 160, your power wheel setting to 1 and your hammer spring setting at 1, and you still got a pellet velocity of 860 FPS. (The settings numbers may not be logical, but they are being used for discussion purposes only.) Is it possible that one combination would get a good grouping and the other setting combination would not get a good grouping, even though they both were sending the pellet at the same 850 FPS? Like all airgunners I would like to get as much pellet velocity, and energy (knockdown), , with as little noise as possible.

 

[jps2486]

I suspect your barrel liner isn't producing good accuracy. I don't know what you have, but I would consider getting a Superior barrel liner.

 

[Oldandintheway]

Thanks for your advice, I would gladly buy one, but they don't make them for a .35 cal.

 

[CoyoteGod]

Oh that hunting balance we all strive for is a real sucker isn't it? I know the .35 impacts do not do slugs, they are 81gr pellet guns only with the stock stuff. Not sure if "bullet" means slug or pellet. I have come to accept that you have to give to get in this scenario. The questions... what are you hunting and at what anticipated distance? What FPE do you want to take that animal? Then you need to go for that energy. Let's say coyote at 100 yards. 70-80 FPE is good for that, calculate what speed you need for the ammo you are using and then test. Work to get best groups for that speed, if it is 3" at 100, and the animal you are hunting is coyote size, that's the perfectly acceptable and will work great because the kill zone is larger than 3".

Where the allowance comes in the hunting rifle tunes is these are not typically "tac drivers" because we want speed and power, and with pellets that's tough at a certain speed point. But there is a good theory I was taught, the slower heavy projectile can actually be more effective in hunting because it transfers more energy to the animal instead of pass through too quickly. Again balance. So for a larger animal like a coyote or bigger (assuming with a 35 you are going bigger) a 3" group is totally a killer. However even at 750ish the power from a 81-gr pellet is totally fine for coyote sized animals if that gives you best accuracy.

 

[tor47]

According to your question 160 bar reg, and hammer wheel at 1, would shoot much slower than with 135 bar, and hammer wheel on 3. You would need to set both hammer wheel higher, and/or have valve adjuster equal or further out than with 135 bar.I would personally never jump from 135 bar, and up to 160 in one go, when tuning, but rather go in steps like 5 bars.

Maybe you would get better accuracy by lowering reg pressure, and aim for a velocity inbetween 715, and 860? If you really want to find out, you can aim for 750, and slowly increase both reg (in 5 bar incements) and hammer, till you reach 800-830? Then you can pick the setting you like best. Do not know what reg 750 fps will require, but just set reg and hammer on the lowest, and work slowly up one step at a time.