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Marauder .25 Cal after a little TLC

10 Minutes of Bench Time, a 1/4" allen wrench, and a chrony
Benjamin Marauder PCP Air Rifle, Synthetic Stock- .22 Cal Ambidextrous Synthetic Stock With Adjustable Comb

Benjamin Marauder PCP Air Rifle, Synthetic Stock- .25 Cal
Ambidextrous Synthetic Stock With Adjustable Comb

I was not sure what to expect in my initial review of the new Synthetic .25 cal Marauder. I thought it would shoot and act just like the original. Well, that’s what I get for thinking. If you take a look at the video, or read the video transcript here on Airgun Depot, you’ll see that the shot count was not that great and there was no power (velocity) curve. I did get some very good groups with the JSB Kings, but I knew there was more that this rifle could deliver. The beauty of the Marauder line is that you can easily tweak the rifles to behave to your liking rather than how they come out of the box. This is what we are going to take a look at today.

Understanding the basics

So how do you adjust the Benjamin Marauder series of Airguns? Well, the first thing you need to do is read the manual. Then, you need to purchase a chronograph if you don’t already have one, because you can’t adjust the Marauder effectively without one.

There are 3 basic adjustments which are clearly defined in the manual. There’s the hammer tension (hammer preload), the hammer stroke, and the metering valve. The hammer tension adjustment effects how hard the hammer hits the valve. The hammer stroke effects how long the hammer will travel before it hits the valve, and lastly, the metering screw adjusts how much air is allowed to pass through the valve and send the pellet down the barrel. Have you ever tried to balance a baseball bat on your nose, I believe that would actually be easier than trying to get all these adjustments “just right.”

Most of the time these are set for general airgunning and really dont’ need any adjustments. Unfortunately my test Marauder was not one of these. It needed some work.

Little nip, little tuck, totally new gun

Marauder through the Chrony

Marauder through the Chrony

In order for my tests to have any consistency, I need to be able to fill my Marauder to the same relative pressure. To accomplish this I’m using the Air Venturi carbon fiber regulated fill bottle. It’s regulated to 2900 psi (+/- 100 psi margin of error) and it’s tagging the 3000 psi mark each and every time on the Marauder when I top it off so I’m pretty certain that my fills are consistent enough.

The first shot string I took was of the factory settings. I’m shooting 25.4 grain JSBs over a PACT Professional Chrony.

High – 889.2, Low – 857.5, Average – 876.8, Extreme Spread – 31.7, Standard Deviation – 11.6

1-889.2
2-888.8
3-885.2
4-881.1
5-876.6
6-871.1
7-864.8
8-857.5

As you can see there is no discernible shot curve. These are essentially the results that I got during my initial tests. The Extreme Spread through the 2nd mag opened up to almost 100+ FPS.

Adjusting the 25 Cal Marauder

Adjusting the 25 Cal Marauder

Given my experience with the Marauders, I was hoping that just reducing the hammer tension would do the trick. So, I backed out the hammer spring completely. My allen wrench only allows me to make half turns so I just counted those vs full turns. The hammer spring bottomed out around 9.5 half turns of the wrench. It’s critical that you always record your starting point. If you don’t, you may never be able to put things back to factory specifications.

As a starting point I turned in the hammer spring by 7 half turns and then tested the rifle. I’m very happy with these initial results. Again shooting JSB 25.4 grain pellets but this time 2 full mags which is 16 shots vs the original 8 shots from our first group.

High – 838.1, Low – 814.4, Average – 830.7, Extreme Spread – 23.7, Standard Deviation – 8.2

1-831.7
2-834.9
3-838.1
4-835.5
5-838.1
6-838.1
7-838.1
8-837.9
9-834.5
10-835.5
11-829.2
12-825.6
13-822.0
14-820.1
15-817.7
16-814.4

As you can see, it looks like I’m coming in right near the top of the power curve. Getting 16 shots with this kind of consistency is what it’s all about.

Close, but I think I can do better!

In my final adjustment I wanted to try coming in just a bit more in front of the power curve so I backed out the hammer spring another half turn. I’m currently sitting at 6, half turns from bottomed out. Here are the results:

High – 831.3, Low – 810.5, Average – 824.0, Extreme Spread – 20.8, Standard Deviation – 6.4

1-817.9
2-821.1
3-829.2
4-827.0
5-830.5
6-830.1
7-829.1
8-827.6
9-828.7
10-831.3
11-825.7
12-823.3
13-820.5
14-817.2
15-814.5
16-810.5

While these results yielded a slightly lower average velocity, they reduced the extreme spread and standard deviation to very acceptable levels. The gauge on the rifle reads just a smidge over 2000 psi after 16 shots. These last results are frankly something that I can get pretty excited about here in the shop. Are you ready to see how it did on the range?

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