Most Compact Marauder

Cool build Ackuric!! I love tinkering and that rig takes it to the max. Great work and cool looking too!

Stoti

Click to expand...

Thanks Stoti. Thats one of the biggest thing that keeps me from buying my next pcp airgun. I would have to spend a lot to buy or build another that meets/exceeds my current one. I'm always trying to ponder my next practical upgrade and thats what got it to where it is lol.

Prod's are nice but would truly benefit from 2-4" more of barrel. You have to either push too much air to get pellets into their 'ideal' zone which can deform lead / increase turbulence, or shoot the pellets at a less than ideal speed ie: 700-800 fps. Its a great little carbon (definitely not a pistol hah) but for that reason its only best at really short range and groups begin to open up quickly. JMO! A .177 P-rod would perform much better with the current barrel length they run, less energy but more accurate.

My valve is highly customized to open with very little hammer strike without being balanced. Thats primarily due to a reduced poppet od of .275", which at 1950 psi sees 116~ lbs of pressure that the hammer / spring combo has to overcome, where as a stock marauder even regulated at the same 1950 psi sees 178 lbs of force, an increase of 53%, which means you need 53% more hammer energy. I used to require 10# spring, but if you do the math backwards, going from 178 to 116 is 34% drop, which allows me to run a 7.7# hammer spring instead of a 10 lb. 10 * .34 = 3.4 - 10 = 6.6 lbs. But to achieve the .275" poppet on a .238" seat that flows enough air for the forward .23" and .225" porting requires a custom hss drill rod that is reduced to .045"~ in the throat. I wouldn't advise anyone to reduce stem OD's without knowing the math that goes behind their potential structural failure. I have around 3000 shots on my custom valve stem with reduced OD in the throat without failure. In the event of any failure I would just increase the OD 10-15% as I have enough margin for that without restricting air flow.



Basically all my valve mods have synergy together IMO for a very efficient, powerful and easy to open valve for its power level. Skipping one or any will crutch a valve in one way or another. I chose this route over a balanced valve for simplicity. 



Interesting math for those curious of plenum sizes and their effects. As noted earlier from 20cc to 53cc I went from 56 to 61.4 fpe, that's an increase of 33 cc, or a 165% increase, if I increase it another 160% to 138cc from 53 cc my power only goes up to 63.2 FPE, huge diminishing returns right? 10 cc's would likely limit this setup to 50 FPE, 5 cc's down to 40 fpe. That is because of how the pressure drop works during the shot cycle. Here is a chart showing the effects of plenum size on my particular rifle.







FWIW there would be no considerable change in power going from 120 to 240 cc's of plenum in my current setup...but in a very high powered 240 FPE rifle, it would be entirely different. But as the graph suggests, around 50-100% of intended FPE in volume for plenum measured in CC's is most ideal, and 1/3rd acceptable, below that is very poor for performance, and above marginally better. Hope this helps some understand plenum volume and its importance.



-Matt