Tuning .25 Marauder upgrade

[ChrisS]

So, I have a box stock gen 1 Marauder, shoots well in the low to mid 900fps range with 20 grain pellets. I like to tinker...

I bought one of Cothrans Marauder valves, installed it along with it's matching transfer port, fully expecting a couple hundred fps more velocity.

Well, I get it built and head to the range to test. Velocities are now just a tad LOWER than with the stock valve! I run the preload on the main spring from one end to the other, adjust the hammer delay from one end to the other, no joy. What gives? Should I open up the guage block? Maybe let the thing breathe a bit more?

Help!

Chris

 

[biohazardman]

Your barrel, transfer port and the valve port all need to be matched in size at 75 to 80% of the pellet diameter. They also need to be aligned just right to get the best from your gun. It's pretty easy to get things misaligned a little and it doesn't take much to loose power. I managed 150fpe with this 1/4 inch transfer port on my 9mm, arrowgun with a Cothran valve. So they do work.

 

[ChrisS]

Thanks for that Biohazardman

I'm well aware that Cothran hardware does indeed work, and work well. This is not my first forray into his stuff. Rather, my question is "what have I done wrong"? I know all is aligned properly, the Cothran transfer port will hardly allow any mis-allignment. My question is: "do I need more airflow into the valve"? In the form of either a hogged out Benjamin guage block or an over the counter block such as the Hill unit? Or???

 

[biohazardman]

Oh thanks for the clarification I understand now. Well it should shoot pretty close to what it was before and if that's the best it will do, and the ports are already enlarged a bit, then that pesky gaugeblock is probly holding you back. I delete that block and put a blank in its place when building on the Discovery tubes. Bought a Huma reg for my Ratgun a few weeks back and it had a very nice gauge delete cylinder with it. Even better than the one I made shown below. They make a high power reg with the gauge delete for the Marauder too. It has a larger plenum to keep your gun breathing better. Don't have a marauder though so have not tested one yet.

https://www.huma-air.com/Benjamin-Marauder-High-Power-Tuning-Regulator

 

[Airgunmann]

I've hogged out the gauge blocks before you have to stay off center can be kind of a pain to do . I've also used the hill gauge block a couple times and I would just order the hill gauge block . Your going to want to put a regulator in the gun it will be a descending shot count and not a curve only real way to control the Cothran valve 

 

[ChrisS]

OK, thanks guys. That pretty much confirms what I was thinking. I've ordered the Hill guage block and will hopefully have that in a week to try out. I'd hog out my stock block but I kinda wanted to hang onto that along with the stock valve so I can go back again.