PCP Woes - Too much pressure, too much power

[datilD]

The .22 Benjamin Marauder had been my grail air gun for years.  I finally got my Mrod, and got it sighted in to shoot 1/4" groups at 15 yards (only with JSB Jumbo Exact.. everything else is a fail).  If I had a proper rest, it could easily do better.  The problem that I am having is that it is a beast to fill 2900 PSI with a hand pump, and the 900 FPS velocity is a bit much for back yard pesting.   I know that I can lower the velocity by limiting the airflow with the adjuster screw.  Will using an SSG, lighter spring and reduced hammer weight enable me to effectively use a 2000K fill pressure?  Should I simply cut my losses, sell the Mrod and get a .22 Maximus?  I can restrict the transfer port and use an SSG with a lighter spring, shooting over the chrony to dial in my +/- 700 FPS.  Keeping the velocity in the 700 FPS range is enough for chipmunks and target shooting at 15 yards.

The other issue is that the Mrod is louder than expected.  My .22 FD XS60 PCP with 5.5" TKO LDC is about the same volume, which is definitely not what I would consider quiet.  (The XS60 is also a bit over powered, but I am working on it.)  As such, I have been using my 1377 carbine with TKO LDC to dispatch the vermin.  The only sound is the hammer and pellet smack.  The .177 doesn't have the knockdown power of a .22, and the rodents will often flop for a few seconds.  (The carbine likes Crosman pointed hunting pellets, and will not shoot CPHP.)  With the .22s, it is instant lights out.  With less velocity, I know that I can expect less report and higher shot count.  Is there an approximate transfer port size that I should begin with to lower the velocity of the Marauder or Maximus, before I add and begin tweaking on the SSG?  I can turn a few different transfer ports on my lathe to experiment with, but having an idea of the inner diameter would be helpful.  I have read through nearly all of the SSG threads, and have a pretty good idea of how to adjust it to regulate my shot strings. 

*Using a 2000 PSI fill pressure will enable me to more easily fill with a hand pump, or use an inexpensive SCBA tank from the local dive shop.

Would it be easier to get a Maximus dialed down to 700 FPS than converting the Marauder to shoot at 2000 PSI?
What transfer port size should I start with to lower the velocity?

Thanks in advance!

[TF89]

I'm interested in finding out what people have to say about this.  Something I have wondered about myself.

[Taso1000]

Yes,  you can tune the marauder to work with a 2000 psi starting pressure.  Here is one example to get you started:

https://www.pyramydair.com/blog/2010/12/adjusting-the-benjamin-marauder-for-low-pressure-operation/

There are many more documented setups if you search for them.

Thanks,

Taso

[ezman604]

I'll offer up MY opinion. So you can take it with a grain of salt or sugar, whichever. LOL
I love the Mrod platform. It is so very versatile and so many aftermarket goodies available. And I build my own stuff for it too. But it is a 3,000psi airgun. Yes, you can dial one down to make it a 2,000psi airgun. But for me, it's like buying a Porsche and installing a governor to keep the speed down.
I would suggest getting an airgun more suited to your purpose and adjusting from there. Like a Disco or Maximus. Or an S200. There are several more suitable choices in that power range and air reservoir capacity.
Whatever you choose....
SAFE & Happy Shooting!!!!
Dave
 

[triggertreat]

Derek, you can easily tune the .22 to shoot 700 fps with the 18.13gr or others.  I would leave the VMS fully open at 5.5 turns CCW.  With the VMS closed down, all you are essentially doing is similar to just putting your hand out of the window of a moving car so to speak.  The valve still opens the same amount, but you just put some resistance against the flow when closing the VMS.  For efficiency sake, I would much rather use an SSG tuned properly utilizing the gap to control the velocity.  Short quick burst of air is much better than a long drawn out pulse of air because of some flow restriction.  I am sure you have seen my DIY SSG build which would be cheap and easy to build, but any device that provides a gap or removes preload like the TSS or others will work too.


The higher the fill pressure the better the efficiency and with the Marauder the sweet spot is between 2800 psi and 2100 psi, but you can tune anywhere in the power curve for less shot count.  To fill to only 2000 psi is doable but less efficient.  To do so, I would recommend filling to the midpoint of your desired max fill pressure (around 1600 to 1500 psi) and set your peak velocity there while staying close to the midpoint pressure while you are adjusting the peak then fill to max and run a full string to note any fine tuning needed.  Ideally you should have a centered bell curve with the peak velocity in the middle of your string once tuned correctly.


I would recommend a lighter hammer than stock too and the MDS hammers are light and smooth cocking and are a good substitute for a stock weight hammer.  Keep in mind though that a lighter hammer will require more hammer spring tension to maintain the same velocity that a heavier stock hammer produced.  Also keep in mind that the stock .22 cal valve spring is very stiff and hard to open even at lower fill pressures so consider replacing it with a lighter one for easier cocking effort overall.  I went with the .25 cal valve spring in mine because it is a little weaker than a .22 valve spring.    Lowering the spring rate of the valve spring helps even out the heavier hammer spring requirements when using a lighter hammer.


It is all a balance between the valve opening time (hammer energy), port size and fill pressure.  Keep the ports stock with a low fill pressure in order to keep the bell curve within a usable range and make tuning easier.  Only open ports for max raw velocities or when regulating.  Keep the SSG gap small for a short dwell of air burst and the quietest shot noise possible and the easiest cocking effort.

[Xraycer]

Double load it every time..........problem solved

it's like buying a Porsche and installing a governor to keep the speed down.

That would be a travesty!

[ezman604]

Keith, you have some good points. And I could have filled a response with many suggestions to lower power and extend shot count. But as you stated, the sweet spot for the MRod is generally around the 2100psi area. But as Derek stated, he is hand pumping and filling to 3,000psi is a PITA. Hence my suggestion of a different airgun instead of massive modifications to the MRod.
But again, just my opinion.

[kkarmical]

What kind hand pump are you using?  It was hard going with the Benjamin pump, compared to the Hill pump, maybe a pump upgrade would help. 

For the yard I've been using my Kral w/ power adjuster backed down so I'm sending lead down range @ 490 fps for 7.8fpe which is good for anything I may have to pop a shot at.

If you do end up ditching the Mrod for something else, at its price point Kral to me with the power adjuster makes it one heck of a yard gun.

[K.O.]

Simple tune down for now and keep the Mrod... and save for a disco...  and a T KO ...

A Disco is nice and light...

[Lmgunner13]

Put a WAR TSS on it, tune it for a 2500 psi fill so your shot string hits about 800 at the top of the curve with JSB 18.1 jumbo heavys and you will be good. I can pump my disco with the 3000psi mod up to 2500 easy with my benji pump.

Happy hunting!

Phil

[kbstingwing]

Get a SCBA Fill tank and some headphones and you'll be fine..........
Really.
What everyone said above....
and you can get an extension TKO for it to make it extra quite......

[datilD]

Wow.. Thanks for all of the replies and info!  It will keep me busy reading and researching for a while longer.

I was leaning towards selling the Mrod in favor of a Maximus, but the fact that it is such an accurate .22 made me consider modding it for lower power.  The reviews of the Maximus have indicated that it tends to be accurate, but it a new AG is always a gamble.  Having an AG designed for a 2000 PSI fill is clearly a good starting point.  I have never liked the process of auditioning pellets for a new AG, but it is rewarding to stack pellets after the right one is found.  The rodents don't like it when I start targeting them instead of paper, though.

I am currently using a Xisco hand pump.  It works great for the XS60 PCP, and worked well on a Disco (that I returned due to a brutal leak).  Filling the Mrod is not easy when it gets past 2000 PSI.  As I  mentioned, the other reason for staying with a 2000 PSI fill is that I can pick up a huge 3000 PSI SCBA tank for $125, and get it filled for $7 or $8 locally.  That will give me a lot of fills without using a hand pump. 

[rsterne]

Some info on the Disco with smaller Transfer Ports....



Those were with a stock valve, 2000 psi fill, but a 2260 reservoir (half the volume of a Disco).... You can double the shot count above, using a stock Disco, and only changing the transfer port.... If you are looking for ~ 700 fps with 14.3 gr. pellets, I would try a 0.090" transfer port.... and you should get about 40 shots per fill when properly tuned....

Bob

[LDP]

You could install a reg. It wont really fix the problem of pumping it up but if you reg it to a low tune you will gain a bunch of shots. The low tune reg will also make it very quiet.

[rsterne]

I disagree with the idea of a reg. "gaining a bunch of shots".... They reduce the ES, but seldom gain shots at a given FPE level.... A reg'd PCP tends to be louder than the same FPE gun without a reg. as well.... particularly in the first half of the shot string, where the unregulated gun is operating using tiny sips of high pressure.... which is a very quiet mode of operation....

Bob

[AlanMcD]

You have plenty of options without spending a dime - the Marauder, as designed, is very versatile.  We all have taken it further with aftermarket parts, but you can do a lot with the stock tuning approach.

It has a been several years, but used to run my .22 at about 18 FPE off about a 2600 psi fill in the winter time for indoor target shooting, and I got about 60 shots with an ES under 2%.  Just follow the earlier advice on the lower pressure/power tunes.

[triggertreat]

Keith, you have some good points. And I could have filled a response with many suggestions to lower power and extend shot count. But as you stated, the sweet spot for the MRod is generally around the 2100psi area. But as Derek stated, he is hand pumping and filling to 3,000psi is a PITA. Hence my suggestion of a different airgun instead of massive modifications to the MRod.
But again, just my opinion.

Dave, I couldn't agree more and from my experience at the fun shoot when checking out the Maximus, Derek would really like it and it would align better with his needs like you suggested when hand pumping.  I really wanted to win the raffle drawing on that gun at the fun shoot.  It is very light and easy to handle and I have not heard anything but very good accuracy about that gun.


I agree, tuning a Mrod to a very low velocities is not ideal and I only made suggestions on what I would do if the Mrod is what he decides to stick with.

[LDP]

I disagree with the idea of a reg. "gaining a bunch of shots".... They reduce the ES, but seldom gain shots at a given FPE level.... A reg'd PCP tends to be louder than the same FPE gun without a reg. as well.... particularly in the first half of the shot string, where the unregulated gun is operating using tiny sips of high pressure.... which is a very quiet mode of operation....

Bob

Well Bob you are very experienced but I think you are looking at my comments incorrectly.

stock setup: 3,000 psi and 30 fpe. Its a guess if its 30 fpe but I will assume a stock mrod using a 3,000 psi fill will be a 30 fpe rifle.

reg setup: 1700 or 1800 psi regulated tune, lightweight hammer if needed and still using a 3,000 psi fill. Or an even lower setting on the reg if its still over the power the OP needs.

I will argue that going from that unregulated tune to the regulated one will most certainly increase shot count because properly tuned and setup its going to be sipping tiny bits of air to reach the lower fpe tune the OP is wanting. Also if it is setup correctly it will be quieter. I just regulated my scorpion .177 and its half the noise it was pre reg and every pcp I have added a regulator to that was setup properly has been quieter. I will agree with you that a regulated rifle thats setup for the same fpe that it was shooting pre reg will not gain shots but the OP is wanting less power unless I read his post incorrectly. So yes he will gain a bunch of shots if hes wanting to go from lets say 30 fpe to 15 - 18 fpe and adds a regulator.

[rsterne]

Reducing the power is what increases the shot count, not using a reg. to do so.... You can clearly see that in the chart I posted.... I didn't misunderstand, I merely wanted to emphasize that is the power reduction that increases the shot count....

Bob

[Ol'DeadEye]

Is my memory fooling me, but didn't the tag on my new Gen1 MRod state that it was factory setup for a 2500 lb fill?

Does anyone have a velocity chart for a co2 powered 22 cal  MRod?

I pump to 2500 lb with an Air Force pump and I'm a 71 y.o. couch potato with a bad back.

I'm no "Uncle Ernie" who likes to fiddle about.  (Anyone recognize the reference?)

K.I.S.S.