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Ammo Benjamin Marauder PCP .177-caliber air rifle: Part 4

Benjamin Marauder PCP .177-caliber air rifle: Part 4

by Tom Gaylord, a.k.a. B.B. Pelletier

Part 1
Part 2
Part 3
Secrets of loading the Benjamin Marauder magazine

Benjamin Marauder
Benjamin Marauder

Today, we’ll start learning how to tune the .177 Benjamin Marauder we’re testing. An owner can do two things to his rifle. He can adjust the power (which is the velocity) and he can adjust the maximum fill pressure the reservoir will accept. The power adjustment is straightforward, and I’ll get to it in a moment. The fill pressure is more obscure. Unless you have a good reason to adjust the maximum fill pressure, you should leave it set to 3,000 psi because that will give the greatest number of shots. I’ll adjust the fill pressure in a future report. Right now, we’re looking at just velocity.

The velocity is controlled by a screw that impedes the airflow through the transfer port. The screw enters the port from the underside and goes across the port, blocking a percentage of the air that’s trying to flow through. Since the valve is open only for a short time, this blockage is effective. We’ll see how effective today. First, though, we need to know where the rifle is now.

To get to the adjustment screw, the barreled action is removed from the stock. The adjustment screw is on the right side of the pressure tube, ahead of the trigger unit. There’s a locking screw above the adjustment screw, and both are found deep inside a threaded hole.

Benjamin Marauder adjustment screw

The power adjustment screw is located on the right side of the pressure tube ahead of the trigger.


Benjamin Marauder adjustment screw in rifle
The power adjustment screw is deep inside a threaded hole — beneath a locking screw of the same size.

Benjamin Marauder locking screw
The locking screw is a small headless Allen screw.

I filled the rifle to 3,000 psi and started shooting Crosman Premier 7.9-grain pellets. We already know how accurate they are in this rifle, now let’s see how many good shots I get from a fill.

Benjamin Marauder pressure gauge
When the carbon fiber tank gauge read 3,000 psi, this is what the Marauder gauge looked like. That’s pretty close!

Shots   Shots
1-20     21-40

1014    1018
1014    1016
1020    1014
1018    1012
1019    1014
1020    1008
1026    1009
1021    1003
1026    1004
1023    1002
1028    1002
1028     997*
1029     993
1028     990
1028     991
1026     986
1027     986
1021     988
1025     981
1021     976

* Off the power curve at shot 32.

I rate this as 31 good shots because I’m accepting a 30 f.p.s. velocity spread. Since the high was 1029 f.p.s., the low would be 999 f.p.s. You can set this up any way you like, but you do see that the gun is definitely declining in velocity after the 31st shot. I would say the gun has 3 good magazines on a 3,000 psi fill with this setting.

Crosman advises in the owner’s manual to turn the power adjustment screw all the way in (clockwise) until it stops and to record just how many turns it took. Then, you’ll know where the gun was when you began; and if you ever want to return to that power, you can.

My rifle had 2-1/3 turns on the adjustment screw, as it was set. I left it all the way down, which is as restricted as it gets, and I filled the rifle to 3,000 once more. Next, I started firing the rifle and adjusting the screw after every 2 shots, while recording the velocity with the same Premier pellets.

Lowest power

Screw 1/3 turn out

Screw 2/3 turns out

1 turn out

1-1/3 turn out

1-2/3 turns out

That was where I wanted to be, so I stopped adjusting. I locking down the screw on the adjustment screw and put the barreled action back in the stock. Then, I filled to reservoir to 3,000 psi and started shooting another string.

Shots  Shots
1-25    26- 49

866     897
867     896
877*   892
870    891
874    890
877    889
886    892
887    888
886    884
881    887
880    881
887    883
884    878
884    879
891    877
889   876
892   876
890   874
890    870
893    870
898** 869
895    868***
898    866
897    865

* First good shot.
** Fastest shot
*** Last good shot

Using a velocity variation of 30 f.p.s., the same as for the first string, the fastest shot went 898 f.p.s., so the slowest acceptable shot went 868 f.p.s. There are a total of 45 good shots in this string by that criteria.

But notice that the first 2 shots were slightly below the acceptable range. That’s because 3,000 psi doesn’t work perfectly with this velocity. This is an example of how the fill pressure can also change with the velocity you select. So, the power screw adjustment shown in this report is not independent of the fill-pressure adjustments. It worked out so close this time that we can overlook the 2 slow shots at the beginning of the string; but if you try for a lower velocity average, that will probably change.

This test also gives a good sense of how the velocity average affects the total number of available shots. We went from 31 to 45 good shots by clipping a little more than 100 f.p.s. off the average velocity we would accept. And when you look at the average we’re now getting, which is somewhere around 886 f.p.s., you see that we still have a lot of velocity for serious work such as hunting. The question becomes: Which would you rather have…3 magazines of shots per fill or 5?

As long as the velocity was down below 750 f.p.s., the rifle was incredibly quiet. After it got above that number, it didn’t seem to change much between 750 and 1,000 f.p.s.

It was very straightforward to adjust the Marauder’s power, as you can see. The stock does have to come off, but it isn’t hard to do. Once you’re done, it goes back on just as easily. This isn’t a rifle that invites constant velocity adjustment. You set it and forget it, so the stock removal poses no real problem.

author avatar
Tom Gaylord (B.B. Pelletier)
Tom Gaylord, also known as B.B. Pelletier, provides expert insights to airgunners all over the world on behalf of Pyramyd AIR. He has earned the title The Godfather of Airguns™ for his contributions to the industry, spending many years with AirForce Airguns and starting magazines dedicated to the sport such as Airgun Illustrated.

65 thoughts on “Benjamin Marauder PCP .177-caliber air rifle: Part 4”

  1. I had no idea it would go as low as 424 fps!
    Approximatly how many shots could be had with that fps? If you’re getting around 30 good shots at 1000fps could 60 good shots be achieved at half the power?

    We have someone in Canada who has a permit to modify Marauders and permanently remove the shrouds to make them legal here, maybe that screw could be turned and welded in place so no velocity adjustement could be made and would make it legal to own without license…
    What if Crosman made a batch without the screw?

    I love this blog, there’s always something to make the wheels inside your head turn.


    • By the time you when through all the trouble and expense I think you would be better off to get the license if you can. You would then have the real deal which would do all you needed.


      • The thing is I have to get it unshrouded to start with because shrouds and silencers are illegal here (Canada) and if I do get the firearm license then it will be considered a firearm and will need to registered too and since it will be a firearm I won,t be allowed to shoot it in my backyard and it will be submitted to all laws refering to firearm including storage and transportation which are a pain to deal with.
        If I get it doesn’t go over 500fps and 4,2fpe (you have to go over both limits to be considered a firearm) then it’s the same as a RedRyder if it’s over both limits it becomes the same as a 12 gauge or .338 lapua.


        • It’s too bad you have put up with all that B. The powers that be want the same thing here in the US but so far keep running into the Second Amendment. BTW, my daughter’s boy friend is from Manitoba and loves to go shooting when they visit here. She is in University there.


  2. I would also like to see Crosman take this gun in another direction than what JF describes above in his reply. Reading this, I can see that the Crosman product , for the money , is head and shoulders above the competition in the $500 dollar range of all the guns offered by PA. Now what if Crosman were to increase the size of the pressure tube a bit(longer ?), and barrel it with a .311 barrel that could be used with almost all of the currently offered .30 cal bullet moulds out there? As a single shot would you get ten good shots per a fill? Or take the .25 version and just increase the size of the pressure tube so more useful shots were available? Also maybe make the barrel a firearms bullet compatible bore size as well to take .258 dia as cast bullets instead of the .251 dia pellets?

      • BB, I will be interested in whatever you come up with. I know from many years of shooting and collecting, small bore old school firearms in .25 cal and killing all kinds of small game up to coyote in size, that a pcp that would toss a flat point .25 cal lead bullet at around 850-1200fps would be a very useful addition to any hunters quiver. A .25 cal Lyman #257463 Loverin style is a go to bullet for accuracy in my various .25-20 bolt, slide, and lever actioned rifles for squirrel. The #257420 flat point is another that is good for chucks out to 125 yards or so. Although heavier than the #257420 , the # 257463 is too pointed for clean kills on chucks or game bigger than rabbits in my experience. Within 30-40 yards in a situation where I could be absolutely sure of my shot placement(and where legal ,of course), I would not hesitate to take a deer with any of these bullets.

  3. B.B.,

    I am a paper-puncher and spinner plinker who shoots either at 20-25 yards in my backyard or at 10 meters in my basement. Therefore, what I want from my Marauder (and I have settled on Crosman Premier Lights as the pellet for my rifle) is an average velocity of about 700 fps., and at these short distances variations as much as 12 or so fps. up or down are fine with me.

    Of course I want the most shots per fill. I fill my Marauder with a hand pump. What combination of fill pressure and power adjustment would you estimate would be appropriate?

    Or, am I getting ahead of the report? You’ve indicated hammer adjustments are coming in a future installment.



    • Michael,

      If you mean a velocity spread of 24 f.p.s., then I think you can do it with a Marauder. As close as you shoot, I would look at the 650 f.p.s, range. You ought to get over 60 shots and the accuracy should be great.

      I hadn’t planned on doing something like that, but you can see fro just today’s report how easy it would be.


      • B.B.,

        Yep, you understand me precisely, and 650 fps. would be fine, especially if it allowed for significantly more shots per fill than would 700 fps.

        It would be easy, though? I don’t doubt you. But it would not be simple. Don’t get me wrong; I love my Marauder, but the hammer adjustments multiplied by the power adjuster befuddles me.

        For example, you filled the rifle to 3000 psi. while having the power adjuster all the way in.

        The manual states, “The Marauder has been factory set to an efficient fill pressure that will suit most hunting and target uses.” Would I harm my “factory set” Marauder by filling it all the way to 3000 psi? I have always estimated Crosman “factory set” my rifle’s “fill pressure” for around 2500-2700 psi. maximum, a happy medium between “hunting and target uses,” so I have never pumped it up past that for fear of damaging it (or my Hill pump).


        • The maximum fill pressure remains the same regardless of the setting of the striker preload/stroke (other than a potential for valve lock if using a light/short setting) — the reservoir hasn’t changed.

          The current factory settings — to my understanding — of 2500PSI is relative to the pressure/velocity curve. On mine, starting at 3000PSI, the first ten shots consumed 200PSI; the second 10 also took 200PSI. The third 10 shots, however, only used 100PSI yet had the highest velocities. The 4th 10 used 125PSI, the 5th set used 175PSI, and the 6th used 200PSI.

  4. This Marauder puts out about the same performance as my Discovery which I had to completely pull apart in order to get it to do what the marauder does. I can’t get a Marauder all that easy here due to the shrouded barrel and our state laws which out state law makers secretly enacted on us a few years back. So I had to get a Discovery and start tuning that. I stuck in a max flow valve since I had to reseal it anyway. Then my bolt busted when trying to fire a Gamo round ball that got lodged in the breech. So I installed a long probe bolt. When I discovered the Marauder had adjustable power I put a power adjuster on my Discovery. Now I’m looking at a TKO muzzle device to quiet down my hard hitting Discovery a bit. I recently discovered that my Discovery is hitting targets so hard that it was blasting through the phone book I was using for a backstop and into the closet door behind it. Now I have to patch holes in my closet door. But it appears that a Discovery with some rather involved work put in it can do about everything a Marauder can do except hold 3000 psi. But that is ok. I find pumping a gun to 3000 psi is rather tough. I’m happy with 2000 psi. It kind of sucks that I have to put so much time and work into a gun due to state lawmakers being so scared of shrouded barrel air rifles and air pistols with rifled bores. But I will go the distance to make what I want if I cannot buy what I want. In the end what I am tuning to my specs is just as good and perhaps just a little less inexpensive.

    • John,

      I have the 6-1/2 tko on my .22 Discovery and it quieted down to where I can shoot in my basement without hearing protection. I still shoot through a rolled up carpet down there, but tried it outside of that and it’s still not loud. Adds a bit of length though…


      • I’m looking at the 5″ but the 6.5″ is a happy medium I am also considering since I like the 7.5 but don’t really want all that much length put on the muzzle. I hunt with my guns so the 5″ is more likely what I’d get. Since I’m jazzing up my discovery with all kinds of stainless steel I’m thinking the brushed aluminum will look good on the front of it. It will match the stainless steel breech a bit better. I’m working on selling my Discovery so the flashier I make it the easier it will be to sell. But with all the work and stainless steel going into it the price is also going up since stainless steel is a bit expensive.

  5. I have 3 .177 Marauders, 2 .22 Marauders and 1 .25 Marauder. Only the .25 Marauder of mine was set anywhere near 3,000 psi when I received it. All of the other 5 were set right around 2,500 psi. Are you sure your Marauder was set to 3,000 when you received it or did you modify the settings so that it was “set” for 3000 psi? That just seems very odd to me if it was. I can assure you if you took a Marauder that was set for a 2,500 psi and filled it to 3,000 psi, you would be very disappointed in the velocity of the pellets even with the velocity screw opened up all the way and most likely would think it was broken and want to send it back.

    Also you are doing a disservice to people by saying that 3,000 psi will give you the most number of shots. I can say with my Marauders the maximum PSI does not correlate well to the maximum number of shots. Maximum number of shots correlates much better to the least amount of air wasted per shot. When you waste air every shot, your psi drops more quickly and this will cause you to move out of your optimum fps range more quickly. On my rifles, keeping the velocity within a 30 fps range per shot means keeping the psi in a 400 to 500 psi range. The longer you keep it within the 400 to 500 psi range, the more shots within 30 fps you CAN get (notice I did not say WILL get). Remember, going from 2000 psi down to 1500 psi is EXACTLY the same amount of air as it is going from 3000 psi down to 2500 psi. I have a .177 adjusted for 2000 psi fill pressure (max velocity happens around 1800psi) and get just short of 50 shots with 8.44 JSB averaging 848 fps. PSI drops to between 1600 and 1500psi. (Not really sure why it sometimes reads 1600 and others it is 1500, but it does). I get the shot count because the PSI stays so consistent, not because of a high starting PSI. (If I accidentally put in 2100 or more my shots start out under 800 fps – at 3000 psi they may not even make it out of the barrel)

    • Bob,

      Yes, my rifle was set to 3,000 psi when I received it. My rifle is very old and came from the first production. In fact, you may have missed it but the test rifle is pre-production, and was changed from a left-hand magazine system to a right-hand system.

      As to your comment about the use of air, Bob, all things have to be considered equally. Of course you get more shots at lower velocity by adjusting the hammer spring and valve opening time, but you will get more of them with a 3,000 psi fill than you will with a 2,500 psi fill — all other things being the same. The two strings above show that very well.

      Could I adjust the air to operate at a lower fill pressure? Of course. Could I get the same velocity? Yes, again.

      And, if I were shooting at a lower velocity I might even get a good number of shots. But I will always be able to get more shots from a higher pressure fill. If you could get the same number of shots at the same velocity on a low-pressure fill, everyone would be filling their guns to 1,500 psi. But that only works when your reservoir is huge — so the pressure doesn’t drop off too quick.


      • B.B.,

        How can one tell what maximum fill pressure setting his or Marauder is set to?

        Also, how can a Marauder owner change the maximum fill pressure setting? Must the action be disassembled?


          • B.B.,

            I owe you an apology for being a poor student. If you are Master Po, then I have been an inattentive Grasshopper. You answered my questions, well, a couple of ’em, anyway, before I asked them! D’Oh!

            Your answer to Gunfun1/GF1 at the very top identifies the hammer adjustments as the way to set the (maybe a better way for Crosman to describe it than “set” is “determine the appropriate”) fill pressure. Would a fair preview of the next installment be that the hammer spring pre-load and striking length be within a certain range for a given fill pressure to avoid valve lock and/or exhaust valve inefficiency?

            If yes, then I am finally starting to get a clue, LOL! (If not, then I am still clueless.)

            As always, thanks for your patience,


  6. I am totally doumfounded by your response. As far as I know you are the leading authority (by FAR) in the airgun world.

    What I said was the truth. Your response was once again, doing an injustice to the airgunning community. Your strings did not show that you get more shots at 3000psil. At 2000 psi, I get 48 shots at 13.5 fpe within 30 fps of each other. In your string you got 45 shots with about 13 fpe within a 30 fps range. My guess is that your PSI probablly dropped about 500. We got the essentially the same number of shots at the same FPE BUT our pressures were quite different. Yours was 3000 psi and mine was 2000 psi.

    As far as your 1500 psi comment, I have not been able to get a good shot count from that range. But I am getting A BETTER SHOT COUNT and BETTER FPE at a 2000 psi fill than you are at a 3000 psi fill. That means, at least in this one case, 2000 psi is giving more shots than a 3000psi fill. So you ALWAYS get more the most shots with a 3000 psi fill is FALSE.


    • Bob,

      B.B. wrote in his response “All other things being the same.” Are you getting more shots with a lower fill with everything else being the same?


    • Bob,

      In the next report I plan to reduce the fill pressure — show that it is reduced — and count the shots at the reduced pressure. By “the shots”, I mean those that are of the same velocity that I recorded here.

      So everything will be done in the open, and we’ll all see what reduced pressure gives us.


  7. The bottom line is yes!

    As long as you are within the range that the gun can meet the fps and fpe range (which would be something like 10 to 15 fpe and 30 fps in .177 cal), then you can tune a gun for 2000 psi and have as many shots as a gun well tuned for 3000 psi. You will also find that both will drop between 400 and 500 psi.

    The 2nd issue is that .177 and .22 marauders come tuned for 2500 psi from the factory and suggesting that people fill to 3000 psi would screw them totally. They would be wondering why there guns are shooting at 500 fps even with the screw all the way turned out. IF he wanted a 3000 psi he should have given instructions for how to tune the gun to a 3000 psi fill.

    If you want to tune a .22 cal Marauder to 25 FPE, then you will probably need to increase the fill pressure – with I find the 2500 psi that is the default to be a great starting point.

    If you want 40+ fpe from the .25 cal marauder, you will want 2900 to 3000. I think 2900 is supposed to be the default, but it may be 3000.

    But for a .177 at low to moderate fpe, there is no reason to go for a high psi as it will not increase shot count per fill and will greatly lower the number of shots you get from what ever tank you fill your gun from.

      • B.B.,

        For those who are unlike you and me, my “Master Po” and “Grasshopper” references above are to the early 1970s classic TV show “Kung Fu,” and your “Bully” allusion is to the original Bull Moose (Party member), Theodore Roosevelt.

        O.K. For those under 25 “Teddy” Roosevelt was the 26th President of the United States. For those under 20, “Teddy” Roosevelt is the third face from the right on Mt. Rushmore. For those under 15, Mt. Rushmore is an awe-inspiring National Memorial, located in the picturesque Black Hills of South Dakota. For those under 10, South Dakota was admitted to statehood in 1889, along with North . . . oh, who am I kidding.

        If you are under 10, there is only a one in four chance you can even read this. And who am I kidding — this comment is for those of us who are 50 or older so that we can revel in our false sense of superiority.

        Oh, who am I kidding. FALSE sense of superiority? HAH! ;^)

        Um, sorry for the tangent.


    • So, this is what I found at Crosman.com:

      Starting point:
      First off you should always document your starting point as a base line. If for no other reason than to make sure you can get back to the factory settings. The Marauder (as shipped in .177 cal.) has a velocity profile that starts at 2500 PSI and ends around 2000 PSI, and when shooting 10.5 grain Premiers, will usually average around 853 over 30 shots. We felt this was the best compromise for shooters that could be using a hand pump or a scuba tank to fill the gun. The velocity was also reasonably high enough for longer distances, while still getting a shot count of 30. The gun has a 10 shot magazine, and I like to think in multiples of 10 for shot count when looking at possible combinations.

      I wish this was published in the Owner’s Manual. It should be. Needless to say, I’m probably going to enjoy skipping that last 500psi with the hand pump…

      As I’ve stated elsewhere on this Blog, I’ve not noticed a reduction in accuracy out at 60, 70, 80 shots at 10m. Might think/say otherwise if I had one of those computer target systems telling me that I only scored a 7.2. (At 60+ shots on the second fill (to 3000), the majority of shots are still touching the X on the grids I shoot at, and that’s good enough for me.)

      BTW: I went back a re-read some of Part 3… no Heavy target published, so the group must not have been very impressive. Interesting.

  8. I rate this as 31 good shots because I’m accepting a 30 f.p.s. velocity spread

    Wow… Generous. My ancient (many times reported) burn down with the factory settings had me using a 22fps spread — max: 884, min: 862 (and this IS a .177, 10.7gr Baracuda Match).

    That was a 35-shot string from ~2700 down to ~2200PSI

    Someday I’ll have that basement and can do the adjustments and tests. (With the factory settings, and a 30fps spread I’d be getting 41 shots on a fill, 2880-2080psi

    • Wulfraed,

      You are a demanding taskmaster when it comes to statistical and physical tolerances. You must be a physicist, mathematician, engineer, machinist, or all three. (Seriously, I’d wager that you are one or more of the above, if not by profession, at least by training.)

      I am a short distance shooter, and an admittedly shaky one at that. My Marksman 1911A1 copy and Daisy 179 are perhaps the only airguns (all right now, let’s not start that old “is a catapult gun an airgun” debate again) that I own that limit my marksmanship. I assume every other airgun I own can out-shoot my feeble abilities. OK, that’s not true. I always do better with a 10 meter air rifle than with, say, my 760.

      Nevertheless, for me 24 fps. (total, plus and minus combined) variance is OK. B.B.’s standards are higher. Yours, well, yours are higher yet. I selected 24 fps. because it straddles two of B.B.’s velocity results above. Truth be told, with my (lack of) skill level combined with my shooting distances between 10 meters and 25 yards, frankly, 30 to 35 fps. variance is acceptable to me.

      Add to that the fact that no living thing will be inhumanely injured/killed by one of my lousy shots, and an occasional 20 fps. plus or minus really doesn’t matter in my circumstance.

      The other day I was thinking of an old childhood friend of mine who these days sometimes earns a paycheck leading hunting parties of out-of-towners in the wilds of New Mexico, hunting game medium and reasonably large. His clients include some hunters who are VERY particular about ballistics as they want to put the bullet exactly in one spot and not in any other spot.

      They want to shoot once and watch the animal literally die before it hits the ground, and not out of bloodthirstiness — quite the opposite. My friend has often watched an expert shooter remain very upset for more than two or three days over a kill that took, in the shooter’s belief, longer than it needed to take. An analogy might be if a Sioux killed a buffalo and left too much of the animal unused.

      My buffalo ranges (no pun intended, although I do like it) from 10 meter Olympic air rifle targets to plate steel spinners and aluminum cans. If they die slowly, I couldn’t care less!


      • Software Engineer

        My actual skills with the guns needs lots of work… My last time at a range I was attempting to sight in two spring guns, two PCPs, a .17HMR and a .308Win.

        And I’m afraid I have to confess that only gun of the six I’d be willing to bet I could hit a squirrel with was the .308Win — I managed to get 8 shots into a spread about the size of a standing fox squirrel at 50yards, just before the range closed for the day.

  9. Everyone,

    We are talking but not communicating. I talk about the max reservoir fill pressure, meaning that pressure at which the valve operates within acceptable velocity tolerances and Wulfraed responds by saying that the fill pressure remains the same because the tank is rated to that pressure. I’m talking efficiency and he’s talking pressure safety ratings. That’s apples and oranges.

    I say that 31 f.p.s. is an acceptable velocity spread for a 25-yard gun and he says I’m being generous. Okay, we will do a test.

    I will shoot 2 groups at 25 yards with the gun set to 20 f.p.s. variation and two more with the gun set to 40 f.p.s. variation, and we’ll see what that does to the groups. If the extra 20 f.p.s. tolerance makes a difference we should be able to see it.

    I can’t design a test to demonstrate the maximum fill pressure concept, because we aren’t talking about the same things. So I will be extra clear in the next report to define what I mean by maximum fill pressure. That’s the best I can do.


    • Oh, and the “generosity” comment should have been taken to be deprecating to me… Not a challenge to you. I don’t have the experience to know how much variance in point of impact a larger spread would produce (and given my skill level, why compound it with more variables).

    • Hi folks – I’m new to this PCP game, awaiting the delivery of a .22 Marauder I purchased from PA. Now I’m thinking “Crap what did I get myself into?”. You guys are making my head hurt! I tried a Benj Trail XL and didn’t like the limitations that the recoil of a heavy springer has (POI shift with different holds, braced or freestanding, etc.) so I thought these PCPs might be more like my old laser accurate Silver Streak that as a kid I could hit flies with at 30 feet. (I hand load a fair amount of rifle ammo for target shooting and medium/large game hunting and that has a lot of variables.) Now I see that the air rifle I thought would be straight forward and relatively simple to do some backyard/forest practice and pest depredation with, may be even more complicated than hand loading for a 270 Winchester and shooting 3 – 4″ groups it at 500 yards!

      Okay so here’s my first question- Which variables should be held constant, and which one should be changed when first trying to determine an accurate “load” with my new Marauder? Its easy to see that the PSI and velocity and pellet weight will all affect velocity and accuracy. Should I start out by just leaving all factory settings as is, pumping to 2500 psi, and then try several different pellet brands/models and see which produces the best groups / tightest ES over 30 – 40 shots? Then move on to changing PSI, or then move on to changing velocity, or???

      This reminds me of selecting the best primer, powder type, powder charge & seating depth for a given bullet when hand loading for a high power rifle. Oh, except with the PCPs you’re also worried about how many shots you’ll get out of a fill. Should I just return this thing, shoot pests with a 22LR, tell my new neighbors to stuff it, and hire a roofer to repair the holes I put in my roof?? Ooops that’s more than 1 question. Meanwhile I need to get on with deer hunting next month and get to stacking firewood! Seriously, can’t wait for my new Mrod!

      • Timberwalker,

        You have just asked for a PhD in PCPs in 10 minutes. What you have asked is the equivalent of someone new to reloading asking for instructions on how to load .338 Win. Mag. cartridges to give 3-inch groups at 500 yards and have no recoil in a 6 lb. rifle.

        Shoot your Marauder exactly as the factory sent it for at least a thousand shots. Experiment with the best pellets you see in this blog report. Fill the gun to 2500 psi and then fill to 3000 and see what it does on paper at 40-50 yards. Forget the chronograph for the time being.

        You need to become familiar with the rifle before you can start developing any “reloads” of pressure and pellet type. When you can shoot sub inch 10-shot groups atv 50 yards you will have enough experience with the rifle to begin experimenting. The instructions of how to do that are all in this blog series.

        You are on a very early report. Go to this link to see the rest:


        Welcome to the blog.


  10. I removed the lock/jam screw for the velocity metering screw and drilled a hole in the stock over its location. Now it’s a quick adjustment to go from a low velocity/high shot count plinker to a hunter. This also makes it much easier to find the best velocity for a given pellet based on group sizes.

  11. Feinwerk.
    I have that done to my Marauders also. It works out nice.

    And I think what BB is trying to explain about fill pressure is how effectively the hammer and striker are controlling the opening of the valve at a given pressure.
    It doesn’t mean that the gun has to be set at 3000 psi. It just means that the hammer and striker adjustment needs to be set correctly for that fill pressure to give the best performance.

    I think I explained that correctly.

    • Now the next thing that plays into the equation.

      Fit of the pellet to the barrel. What happens when the pellet fits a little looser to the barrel. More air will blow by the pellet instead of using the air efficiently.

      Got to have the main pellet figured out that you are going to shoot before you start tuning. Alot of the better pellets also come in different head sizes.

      Maybe I’m jumping the gun (no pun intended) so to speak. BB I know you are trying to keep the same variables. But I know what I been through with the pellets to get my guns efficient and accurate. Its alot of work to get it right.

  12. Hi! Nice work, and just goes to show that the combinations are limitless, and that the highest fill-pressure of 3000psi is not necessarily the best. You just move your usable pressure-area up in range, with more pumps required per fill, and not much gain in the number of shots.

    What I’d like to see on the Marauder, is the implentation of a ‘constant-pressure-valve’ (they DO exist you know).
    Thus the air-pressure the gun is getting from the reservoir, is always the same. That way the gun can be tuned to work perfectly on let’s say 1000 psi, and we would get TOTALLY consistant shooting from 3000 to 1000psi!

    This would eliminate the need for any ‘hammer/spring/stroke adjustments, give us tons of extra shots per fill, and the only thing we would have to worry about was the speed knob 😀

    Just a thought…

    • Kim,

      Welcome to the blog!

      Constant pressure system do exist, as you have said. Here in the U.S.,, we call them pressure regulators. They do keep the pressure that the firing valve “sees” at a constant level, hence the velocity remains constant and you get more shots from the gun.

      But even regulators have limits. I think the largest span of air pressure I haver seen was under 1,500 psi. So there are limits.

      Only the Crosman electronic valve that is in the Rogue is without limits, and even then there are other limits imposed by what low pressure air can do in a barrel of a certain length. But that would be the smartest thing Crosman could do — to adapt the Rogue valve to a smallbore rifle.


    • This would eliminate the need for any ‘hammer/spring/stroke adjustments, give us tons of extra shots per fill, and the only thing we would have to worry about was the speed knob 😀

      Even with a regulator, you’d still want some of those adjustments. After all, some pellets may be sensitive the flow RATE — a heavy slow accelerating pellet might want a lower initial pressure but with a longer delivery to maintain pressure as it moves down the barrel. Counterwise, a quick light pellet might respond better to a fast shorter duration flow — yet with the same maximum/regulated pressure.

      Where the regulator helps is in removing the effects of partial valve lock at the pressures above optimal — giving a number of “flat” shots before the pressure falls below the regulator setting.

  13. I guess then these are issues we will have to live with, to some degree at least, if we are not to have electronics on the rifle. What we are dealing with is a tank of air where the pressure gets lower by every shot, and yet we demand the rifle to shoot exactly the same each time…

    What I envisioned was a pressure regulator combined with a smaller secondary tank of air. The rifle is fed from the secondary tank, which always hold the right pressure.
    The secondary tank would be made just big enough to not be emptied when the shot fires, maybe hold as much as 5-10 times the amount needed, to avoid the problems Wulfraed mentions.
    But surely Crosman would have thought of this if it was feasable.

  14. Hello, I have a Benjamin Marauder .177 and I would like to adjust the power so that it has about 280 m / s, 25/30 joules , and at least 30 shots helpful. Can you tell me how many turns of hammer spring, stroke and transfer port are needed?
    Using pellets H & N Barracuda Match 0.69 gr.


    • Enrico,

      Unfortunately I cannot tell you. Each rifle is unique. You have to test it as I did here, so you will know what it does.

      I would use a 3,000 psi fill level, though, because you want a lot of shots with a lot of power.

      Here is a hint — open the transfer port up first, then adjust the stroke and hammer tension. You will need as much air as the rifle has to offer, to get what you desire.

      You might also rad this other blog report:



  15. Hi, after finding the right settings, the Benjamin yesterday suddenly started to lose air from the valve, I removed and I verified that the valve stem overmolded 1763-140 has a rib on one side of the cylinder of black plastic and let the air from the hole of the transfer port.
    And ‘possible to repair it or you have to change all the valve body?


  16. hi was wondering if i want full power on my marauder and turn the screw out to open it full.will the screw come completely out then.if so will it just be to screw it back in ?

    • Jon,

      It it a captive screw? I don’t know, but since it is a headless Allen screw it probably will come out. I have never screwed it out that far.

      If you are using a chronograph to measure the velocity you will see that you reach the max velocity long before the screw is backed all the way out. So it isn’t necessary to do that. All the screw does is intrude into a transfer port channel to block some of the air. When it is all the way out, the channel will be open, but air will also bleed out of the screw hole.

      Use a chronograph and don’t back the screw all the way out.


  17. BB – Thank you for your lightspeed reply!

    Still awaiting my first PCP, a synthetic Marauder. A Disco might have been fine, but I was concerned about the noise, and also about the legality of a “brake” here in Calif. (freakin’ paranoid anti-gun liberals and draconian ATF), so I opted for the Marauder.
    Then, reading these blogs, my head was about to explode! I had no idea the tweaking of parameters for accuracy would involve this much and was daunted by all of this discussion. But now that I’ve downloaded the manual and read through it I’m understanding what you’re talking about much better. That’s a start anyway. When I bought it I knew there were some adjustments not available on the Discovery but now I see how spring preload tension, striker travel, transfer valve and pressure levels can be adjusted, but I don’t pretend to have any grip on a formula of interaction.

    I will do as you suggest and put a lot of lead down the tube with factory settings before attempting to modify anything. But I am a bit obsessed with quantifying things so I will be shooting over my ProChrono early on. I did that even with the NP2 XL springer I had for 2 weeks before the scope mount (with scope of course) flew off. I found that even 700fps does quite a number on squirrels at 30 yards. In fact a significant part of the motivation of getting an airgun in the first place is now gone (for now anyway; I’m sure their associates will fill the void). Also, there was a forest fire at my normal shooting range and it will be closed for a while so this will be a good way to feed my shooting addiction for a while.

    Thanks again for your sage advice.

    • Timberwalker,

      I understand about your head exploding! Believe me, I have been there many times myself.

      Yes, there is a lot you can do with a Marauder, but take it in baby steps until you gain a feel for how the gun reacts. I would leave the factory settings where they are until I knew I could do better.

      These reports explore a lot — sometimes way more than is necessary. I do that to demonstrate what matters and what doesn’t. But when you read it — it looks like you have to try everything,

      You really don’t. Stick with Premier pellets and JSBs and the factory settings and you will be almost where you want to be from the start.


  18. Hey, I am completely new with pcp air rifles, I just got my marauder about 3-4 weeks ago. Do I have to de-pressurize the air reservoir when I take the stock off and adjust the velocity screw?

      • Thank you. So not even when you adjust the velocity? Is there any possibility to take the screw out completely? Sorry that I’m asking stupid questions but I want to be 100% sure that nothing goes wrong

              • Degasser is also used to air out tank in case you want to switch to CO2.
                I got my Benjamin Mrod .22 two weeks ago and label on the trigger read: Factory set to 3000psi for most hunting needs. Does that mean I don’t have to mess with opening any screws for more power?

                • Adin,

                  Welcome to the blog.

                  What that means is you can fill to 3000 psi without worries about valve lock.

                  The power is determined by the air transfer port and the striker spring strength, which are different adjustments, but are related to the fill pressure.

                  Your gun is probably set at the top power right now.


  19. I recently picked up my second, first generation Marauder previously well enjoyed in .177 for four hundred bucks.

    I already had a .22 that turns 2 x 4’s into swiss cheese so something less formidable was the goal.

    Starting fill of 2500 psi with my .177 m-rod. Not to much trouble with a hand pump.

    I WAS getting 30 shots (well 32, but 3 clips) at 850 fps with 10.5gr CPHP’s. Accurate and lethal at 17 foot pounds of energy.

    Overkill for pure plinking pleasure.

    I have repeatedly, over the last 25 years, dispatched starlings at 30 yards with one shot from my “lowly” Diana 24 shooting 7.9gr crosman pointed pellets hovering around 500 fps.

    I was trying for “that” tune.

    Using only the velocity adjustment screw so as NOT to ruin a good thing, I started ALL the way in and got mid 400’s for a clip. Not sufficient for much more than paper, but QUIET.

    At 3/4 turns out from full in I got a second clip at 542 fps. Perfect!

    100 shots later it was at 570 fps. Okay, now there was only half a tin of pellets left, let’s see how far it will go.

    At 200 shots – that is correct, 200 SHOTS (!) it was down to 513 fps at 1500 psi on the gauge.

    THAT is a ton of fun for a four hundred dollar gun!

    • Sounds like a blast!
      I’m very happy for you and your shooing buds.
      working on my 4th fill with a2400iKT and a HIpac filled to 2000 , or ( just gettin’ started ) but I’m really glad I finally spent the extra money it takes to do the PCP thing! I’m working on trying to get my offhand right again.
      The pump moves so much more air than any multipump I’ve ever pumped that I seem to be Getting2.5 shots on 3 pumps.

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