My 25 cal Marauder. I need help!

[Skip-in-WV]

Goal: with a 25.4 grain pellet. 40 ft lbs. That equals about 850 fps. 

Here is what I've done so far: 
1. Installed a heavier hammer spring. Max speed 900, but terrible power curve with 
only 10 good shots, averaging 875fps. 
2. Installed a Lane Mk8 regulator. Max speed 750 
2. Added an FFH. Max speed 750 
4. Replaced the TP with a piece of tubing. Max speed 750. 
5. Replaced that valve spring with a lighter one. Max speed 750 
6. Added a Lane regulator extension tube for an additional 10cc volume. Max speed 
750. 

As I see it I have 3 options left 
1. Increase the regulator pressure. 
2. Increase the TP hole in the valve. 
3. Increase the TP hole in the barrel. 

If any of that works remove the 10cc extension and see what happens. 
I hope someone has some other suggestions?

 

[Alan]

I wonder what the regulator is set at??? My bottled and regulated .25 Marauder is set at 2,200. The hammer is stock, but driven with a twin spring system from A.R.T. Set all the way back, it shoots 25.4 grain AirArms at 880 FPS, with 3/4 inch groups at 75 yards. I can get over 1,100 with the 34 grainers, but the accuracy is lousy.

Oh! The transfer port is .182. 

 

[Quintoona]

For what you're looking for I think you'll need a different or modified valve.

 

[Alan]

My valve is stock Benjamin, with only the port a bit larger. While the 10 CC addition might help some, if you want high shot count, you almost have to bottle it. Once we know the regulator pressure, we can probably figure out the next step. 

 

[parallax]

I'm guessing more regulator pressure will help. For comparison, my .25 with a Huma set at 2100 psi makes 800 fps with 25.4g JSB. I also have a lower rate value spring, tubing transfer port & TSS. I agree with Quintoona, a more efficient value might be the correct solution. Check out the Marauder forum, there are many threads discussing 40 ft-lbs with a regulator. Hopefully Dairyboy will see this post, he is really knowledgeable on the Marauder platform - perhaps send him a PM. Good luck & let us know how your build turns out.

 

[Skip-in-WV]

Which port? The barrel one or the valve one? I've all ready replaced the brass port with a piece of ployetheylene tubing.

 

[ackuric]

"Alan"I wonder what the regulator is set at??? My bottled and regulated .25 Marauder is set at 2,200. The hammer is stock, but driven with a twin spring system fro
m A.R.T. Set all the way back, it shoots 25.4 grain AirArms at 880 FPS, with 3/4 inch groups at 75 yards. I can get over 1,100 with the 34 grainers, but the accuracy is lousy.

Oh! The transfer port is .182.

over 1,100 fps with 34 gr out of a 19.5" marauder barrel with .182" ports is not likely possible...certainly not at 2200 psi.

-Matt

 

[Wager]

I've done a lot of work on the Marauder platform, lol and own to many. Idk about over 1100 fps but I think getting close to 1100fps is doable with that set up plus a aftermarket valve. But, if you weren't using a balanced valve and stayed with the standard knock open valve you would have a hard time cocking it because the hammer spring pressure.

Skip,
If you leave the barrel and valve port the same size and change just the transfer port you won't see much of a difference even if the transfer port is .20 it will always be limited to the smallest section. You can open up the barrel, and valve port to .187 pretty safely just take your time and make sure to clean out any burs. I've opened everything on one of mine to .20 all the way through the porting but that is really pushing it with out having to do a lot more to make everything work!!! If you have the ability, you Can rework the stock Marauder valve and make a pretty decent one. But there still not quite as good as a Hill valve when it comes to mad power.