I'm not so sure you can reach 60 FPE with an MRod valve at 1800-2000 psi, although you can at 3000.... Since you are starting from scratch, I would use the larger sizes, there is no disadvantage other than the heavier hammer strike required.... and you can push upward to about 100 FPE shooting 50 gr. slugs at 3000 psi.... Here are the sizes I used in the valve for the Millenium Pumper, and for my .30 cal Grizzly (FD-PCP based) gun....Barrel port - 3/16" x 1/4" for .25 cal (7/32" hole for .30 cal)Transfer port - 7/32" (0.219")Exhaust port - 7/32" (0.219")Valve throat - 17/64" (0.266")Valve stem - 1/8" - giving the equivalvent area of a hole 0.235" diameterThis size is capable of 60 FPE at 2000 psi in .25 cal.... and 100 FPE at 2200 psi in .30 cal.... with reasonable efficiency (over 1.0 FPE/CI) and using pellets.... You can achieve higher power levels (at reduced efficiency) of course.... particularly if you use heavier bullets.... As a rough guide, a hammer weighing 100 gr. with an inch of travel, powered by a QB 7X hammer spring or similar, should put you in the ballpark.... If you can use one, the poppet from an MRod will work perfectly with the above sizes, up to 3000 psi.... no need to use PEEK, Delrin is just fine....Bob
Thanks Bob, I was planning on going with 75%-80% of bore based on some of your other posts I have read. This was exactly the confirmation and push I needed to get some stuff done. Bill, it's a ground up build. I'm using a 1.5"OD titanium tube so a Marauder valve is not going to work out. I also don't think I'm going to pin the valve. I don't like the design requirements to pin @ 1.5"OD forces. I know its doable but threading sounds much easier to accomplish all the safety factors I want and the design I want. That and I have a lathe that has a through hole that will fit the tube. The valve and end cap/fill adapter will be 7075. One thing I'm stuck on is how I'm going to make the Ti tube black. Doesn't seem like you can anodize Ti black so maybe powder coating.