Varied Velocites

[El Zilcho]

So after many frustrating hours tuning my X valve w/ ULT I learned one very important lesson, trigger rod length is a big deal :wow: I have everything just about where I want it but have noticed an odd phenomenon, the first shot in a string dribbles out of the end of the barrel (it almost sounds like chuffing), to the point where I have actually hit the 1st ball with the 2nd ball in the string. When I chrono'ed my 1st shot was often in the 170 fps range, my second and third shots would be in the 250 range. When I fired a quick string my last shot regularly climbed into the 280 range.

I think I recall reading that the faster the string with the X valve the higher the velocity will be but, is it normal to jump from 250 to 280 fps (excluding the 1st shot) depending on how fast the string is?

[athomas]

The velocity climb depends a lot on the input pressure. A higher input pressure will result in a more dramatic velocity increase at higher rates of fire. A 30fps jump is a bit high though.

The first shot drop off is a symptom of bolt stick due to having a carrier size that is too small. Have you tried the next larger carrier size with the same powertube carrier oring that you are using now? Make sure you remove the powertube shims if you are testing carriers.

[El Zilcho]

The velocity climb depends a lot on the input pressure. A higher input pressure will result in a more dramatic velocity increase at higher rates of fire. A 30fps jump is a bit high though.

The first shot drop off is a symptom of bolt stick due to having a carrier size that is too small. Have you tried the next larger carrier size with the same powertube carrier oring that you are using now? Make sure you remove the powertube shims if you are testing carriers.
I have not tried the next carrier size because I don't have one, ha, I will have to order one, I am running a 68/45 SHP ninja tank, I think the it is shimmed to 1100 PSI now, perhaps I will drop the output pressure and see what happens. Thanks for the input.

[athomas]

If you don't have any extra carriers, you should order a set. It will be critical for tuning, especially if you need to change your oring due to damage or wear. You never know what the size tolerance on the orings is going to be.

[El Zilcho]

I only have the 1st four I think, I need order a few small things from AGD anyways, so I can add those to the list