Crosman recently released our new Marauder PCP gun, and one of the features that make it different from its predecessor, the Discovery, is its adjustability. In fact it is probably the most adjustable PCP gun on the market. This also makes it one of the most versatile guns. Its adjustable hammer energy and valve transfer port allow the gun to operate at fill pressures between 2,000 and 3,000 psi, and at various velocities. Due to these inherent features we are often asked about making adjustments for various shooting purposes. Our own factory sponsored team of Ray and Hans Apelles have a very in depth adjustment procedure that is a must read. It can be found here:
A-Team Tuning Procedure

This July a number of Crosman employees will be participating in a Field Target shoot in Binghamton, New York NERFTC. As that date is rapidly approaching, I started to consider what equipment to bring. That naturally got me thinking about how best to set up our new Marauder for optimum performance for long distance shooting.

Let me first preface this by saying I should not be confused with an expert in any shooting discipline in general, and field target in particular (that is why we worked with Hans and Ray Apelles on this project). I am also not the Engineer that designed the Marauder (that’s Russ), or the Premier Pellet (that of course, was Bob Holtz). I am just lucky to have worked with them all. Furthermore, I am not claiming that these velocity profiles are the best that can be achieved or that if you dial your gun in at the same setting you will get the same results. Your mileage may vary. This is just my opinion and thought process as I got my gun ready to shoot this match. I do hope this helps to illustrate

Here are some adjustment options and how I document them:

  • What I am labeling “Hammer Tension” the manual calls “Hammer Spring Pre-load adjuster” and for shorthand, I label “H”. When I say ”6 H”, I mean that the hammer adjustment is six revolutions in (clockwise) from the minimum starting point of completely (counterclockwise) out.
  • “Stroke Adjustment” is what the manual calls “adjusting the striker” or “hammer stroke” and I am using “S” as my shorthand. So “2.5 S” is shorthand for when you have the stroke adjusted two and a half revolutions in (clockwise) from the maximum starting point of completely (counterclockwise) out.
  • The “Transfer Port Adjustment” is what the manual calls the “metering screw” and I am using “V” as short hand (for velocity or “venturi “). The starting point is all the way (clockwise) in.

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.

Marauder Tuning Chart

Caliber – 177
Grains – 10.5
Hammer Tension (H) – 3
Stroke Adjustment (S) – 2.0
PSI Fill– 2500
PSI End – 2000
Pumps to Recharge – 44
Transfer Port Adjustment (V) – 2
Minimum Velocity- 837
Maximum Velocity– 862
Average Velocity – 853
Median Velocity – 855
Standard Deviation – 7.20
Extreme Spread – 25
Average FTLBS – 17.0
Cumulative FTLBs – 509.1
# Shots – 30
# of pumps per shot – 1.5
Foot pounds per pump (FtripleP) – 11.6

Faster is better
First I wanted to see the highest velocity I could achieve so as to get the flattest trajectory. I used the 10.5 grain Crosman premier heavy (CPH), as I have had the best results with them in this gun.

Marauder Chart

Caliber – .177
Grains – 10.5
Hammer Tension (H) – 6
Stroke Adjustment (S) – 0.0
PSI Fill – 3000
PSI End – 2200
Pumps to Recharge – 65
Transfer Port Adjustment (V) – 4
Minimum Velocity – 1007
Maximum Velocity – 1039
Average Velocity – 1025
Median Velocity – 1025
Standard Deviation – 9.32
Extreme Spread – 32
Average FTLBS – 24.5
Cumulative FTLBs – 490.0

# Shots – 20
# of pumps per shot – 3.3
# Foot pounds per pump (FtripleP) – 7.5

As you can see in order to get up to 25 foot pounds of energy (FPE), I needed to open the Transfer Port (V) out to max of four turns ( V 4). I also started at 3000 psi and had the longest stroke adjustment (S 0). The numbers I look at for longer range shooting try and keep the velocity spread under 30, the standard deviation under 9, and ideally below 5. I was a little high, but it was as close as I could get with this gun while keeping the other requirements.
Summary: This adjustment would give me plenty of power in case of a windy day, and also the least amount of drop at the 55 yard line. The down side is that the accuracy at this velocity may not be the best that it can be, Bob Holtz used 800 fps to do all his accuracy testing when he developed the Premier pellet. On a more a practical standpoint, I don’t want to have to count on having 3000 psi to fill the gun. If I was hand pumping, it would be too much like work. Most important was that most clubs limit you to around 20 FPE to reduce target damage, so I had to rethink my requirements.

Accuracy is king
My next idea was that if 800 fps was the most accurate velocity, I could probably get 40 good shots and keep in just under 12 FPE needed to shoot with the big boys in International Class.
I also wanted to bring the fill pressure down so that I wouldn’t have to pump as hard. To go under 12 foot pounds I would also change pellets to the Crosman Premier Lites (CPL).

Marauder Tuning Chart

Caliber– 177
Grains– 7.9
Hammer Tension (H)– 4.5
Stroke Adjustment (S)– 6.8
PSI Fill– 2150
PSI End– 1800
Pumps to Recharge – 28
Transfer Port Adjustment (V) – 1.5
Minimum Velocity – 797
Maximum Velocity – 824
Average Velocity – 813
Median Velocity – 814
Standard Deviation – 6.98
Extreme Spread – 27
Average FTLBs – 11.6
Cumulative FTLBs – 463.9

# Shots – 40
# of pumps per shot – 0.7
Foot pounds per pump (FtripleP) – 16.6

So to get the power level down, I turned the metering screw way down to 1.5 V, and backed off on the hammer energy by turning the Stroke in, to almost 7 S. The fill pressure of 2150 seems a little odd, but I just marked the gauge on the gun and filled to that mark.

Summary: I hit the velocity spread and standard deviation numbers that I wanted. I liked the number of shots per fill and it was easy to pump at this pressure. Reality was starting to set in when I considered how much Kentucky windage I was going to have to use. I was not really that good a shot when you consider that I was going to be shooting unsupported in the sitting position. I need all the advantages I can get if I’m not going to use shooting sticks like I did in Hunter class.

The one thing I liked the most was the lower fill pressure so I decided what I wanted was exactly a 2000 psi fill for a starting point. That way I could use one of our 72 cc bottles (add link) and not have to worry about overfilling. Also, I wanted to go back to using the CPH and be at around the factory setting of 850 fps with at least 30 shots.

Marauder Tuning Chart

Caliber – 177
Grains – 10.5
Hammer Tension (H) – 4
Stroke Adjustment (S) – 6.0
PSI Fill – 2000
PSI End – 1655
Pumps to Recharge – 48
Transfer Port Adjustment (V) – 1.75
Minimum Velocity – 822
Maximum Velocity – 856
Average Velocity – 841
Median Velocity – 842
Standard Deviation – 9.27
Extreme Spread – 34
Average FTLBS – 16.5
Cumulative FTLBs – 494.8

# Shots – 30
# of pumps per shot – 1.7
Foot pounds per pump (FtripleP) – 10.3

I did this by opening up the transfer port adjustment to a 1.75 V and with a few hammer adjustments I was in the ball park.

Summary: Close, but not there yet. Unfortunately there was too much velocity variation. I would have to give up some of the shot count.

Fine tuning
Normally when I am trying to get a flatter velocity profile, I decrease transfer port diameter by turning the metering screw (V) in. On this gun it worked out to be the opposite. This just shows that sometimes it is best to make small adjustments and have patience (and a lot of pellets). With a little bit of trial and error, this is what I finally settled on.

Marauder Tuning Chart

Caliber – 177
Grains– 10.5
Hammer Tension (H) – 2.25
Stroke Adjustment (S) – 4.3
PSI Fill – 2000
PSI End – 1655
Pumps to Recharge – 33
Transfer Port Adjustment (V) – 2.125
Minimum Velocity – 840
Maximum Velocity – 857
Average Velocity – 850
Median Velocity – 851
Standard Deviation – 4.76
Extreme Spread – 17
Average FTLBS – 16.8
Cumulative FTLBs – 337.0

# Shots – 20
# of pumps per shot – 1.7
# Foot pounds per pump (FtripleP) – 10.2

If you look back up at the factory settings, you will see that they are not that different. I had come full circle. All I really needed to do was reduce the Stoke to 6.25 S and that would have reduced the hammer energy enough to bring my fill pressure down. This is a good place to point out that if you are having trouble getting the results you want, try increasing (or decreasing) your fill pressure to find the range that works best for you.

Summary: I found the velocity that I wanted and most importantly it was consistent. As I am going to be using the small bottle, it won’t be that much of problem to fill after only 20 shots, and with a 350 psi band of air I am able to get a dozen gun fills from one bottle fill (240 shots). Give it a try and let us know what you think.

Second option

I was happy with the results with the last test, but I decided that I should also see how the gun would shoot at 20 FPE. At this point I was getting the hang of this process and I know that since I had the hammer tuned for the current fill pressure all I should have to do in open up the V adjustment. I set the fill pressure around 1900 psi and adjusted the V screw out until I had a little over 900 fps.

Here is my Chart…

Marauder Tuning Chart

Caliber – 177
Grains – 10.5
Hammer Tension (H) – 2.25
Stroke Adjustment (S) – 4.3
PSI Fill – 2000
PSI End – 1655
Pumps to Recharge – 33
Transfer Port Adjustment (V) – 3
Minimum Velocity – 901
Maximum Velocity – 923
Average Velocity – 913
Median Velocity – 915
Standard Deviation – 7.10
Extreme Spread – 22
Average FTLBS – 19.4
Cumulative FTLBs – 388.8
# Shots – 20
# of pumps per shot – 1.7
#Foot pounds per pump (FtripleP) – 11.8

Summary: The velocity is not as flat as the last one, but acceptable and I have the added advantage of a little more power. Next step is to set up a scope and get out to the range and see what setting shoots best.

Give it a try and let us know what you think.


Warning: Please read your owner’s manual for safe operation of the Marauder, as well as the instructions for making these adjustments. In order to properly make these adjustments, a certain level of familiarly with the fundamentals of a Pre-Charged Pneumatics (PCP) gun is assumed. If you are not comfortable with the procedures talked about here and in the manual, please seek the assistance of a professional Air Gun Smith.

4 Responses

  1. Boris

    I have done very much the same tuning on my own before I found this post. Even used the same legend (H, S, V). My goal was to use it for metallic silhouette at about 20FPE with max velocity spread 20-25 FPS. I have an excel spreadsheet documented the different stages of tune. If you interested, I can e-mail it to you. The best I could do is about 35 shots with 25FPS or 25 shots with 20FPS spread. Fill pressure from 2450 PSI to 2000 PSI.

  2. Kim from Norway

    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, and the only thing we would have to worry about was the speed knob 😀

    Just a thought…