When I first started tuning of my Armada, when I shot over the Chronograph with a 3000psi fill. The best I could get was a 713 fps shot. I thought that was pretty pitiful considering how much I had invested in the gun and I knew a $30 Crosman 760 Pumpmaster could get around 650fps with a .177 pellet right out of the box. 
So, the search was on. I soon found that most unregulated Benjamin Armada/Marauder guns were shooting much better. Out of desperation I asked why my gun was shooting like it was in a Facebook group. Within 15 mins a kind person answered “Check your breech o-ring”.

Marauder Breech .25 o-ring aka #10 (fraction - inch - mm) W 1/16 0.0625 1.5875 ID 1/4 0.25 0.00635 OD 1/8 0.125 0.003175

Sure enough, when I pulled the bolt back and peered into the breech I found the o-ring was gone! I must have shot it down the barrel when firing the first or second clip, seems like I remember forcing a pellet or two into the chamber on my first hand pumped fill. Oh well, live and learn eh?

So, I searched around the house and found a cheap set of o-rings that I had bought at a dollar store for something else, found one that looked about the same size, lubed it with some plumbers silicone grease and stuck it in there. BOOM – instant 100fps increase per shot. By the way, I now run a Durometer 70, and keep spares in my shooting kit.

Below are the results:

Average: 700.7 FPS
SD: 10.7 FPS
Min: 668 FPS
Max: 713 FPS
Spread: 45 FPS
Shot/sec: 0.1
True MV: 715 FPS

Average: 804.4 FPS
SD: 5.5 FPS
Min: 794 FPS
Max: 812 FPS
Spread: 18 FPS
True MV: 820 FPS

Breech o-ring specs:
Some auto parts store’s will call it a #10
Hardware store or online:
Fraction – Inch – Metric
Width 1/16 – 0.0625 – 1.5875
Inside Diameter 1/4 – 0.25 – 0.00635
Outside Diameter 1/8 – 0.125 – 0.003175

Tuning the Benjamin Armada/Marauder

The MarauderAirRifle forum is an excellent source for all info regarding the Benjamin Marauder and the Benjamin Armada 25 (The Armada has the same internals as the Gen 2 Marauder – it’s just dress up to look like an AR15 and out of the box accepts all Picatinny mount accessories).

Below are the settings my rifle shipped with and the Hill Tune that I am using now.

Stock tune for my Armada 
Valve Screw(VS) 3.5 (Clockwise all the way in then Counter Clockwise out (CCW)
Hammer Throw(HT) 3.5 (Clockwise all the way in then Counter Clockwise out (CCW)
Hammer Spring(HS) 4 (Clockwise all the way in then Counter Clockwise out (CCW)
Hill Tune as far as I know, I seen these settings in a post talking about the Hill Tune
VS 5.5 CCW
HS 4.5 CCW
If you head on over to the MarauderAirRifle forum – the Abbreviations below will come in handy when trying to understand what they are talking about if you are new to this sport and PCP airguns in general:

Marauder Air Rifle Forum Abbreviations

I want to say thanks to all the guys who share what they have learned while shooting these guns. I am writing this post so hopefully I can help others in the community, then way I have been helped.

On a side note:
Did I mention how accurate and powerful these magnum air rifles are? 24 rounds punched a hole all the way through my not so trusty well shot up and duct taped sand bag.
So when practicing in your back yard it might be a good idea to place a couple shots in each spot on your target and backstop or the neighbors pets or kids might get hurt. Or maybe put a sheet of 1/4 inch plate steel behind your backstop for insurance.
Please share this blog on Facebook and Twitter. If you would like to post some of your tips and tricks you know feel free to send me an email.
Also, check out the links page. If you have any links you would like to see there. Please let me know.
Oh, and check out the APG Store link in the menu. Sure its an Amazon store, but I did take the time to build it, and the cost to the purchaser is the same. Sure if you make a purchase I might make a few pennies, but I have to support this habit somehow.
Thanks for stopping by, Dan Spechtenhauser



The Beginning

My quest for a PCP air rifle began when I decided to rebuild a 1957 “Benjamin Franklin 317” air rifle that I’ve had laying around for the past 20 years. Over the years I tried to find parts to rebuild it but didn’t have much luck. Till one night I found a complete kit – valve removal tool and all the parts needed on eBay!

I will write about the Benjamin Franklin rebuild process in an upcoming post and list the sources I found and provide images I took during the rebuild process. Perhaps even do a Chrono test to see what this ol boy can do with new parts.

After I bought the parts for the 317. My interest in air rifles began to grow.

The Hunt

So I began researching air rifles. I spent hours on the internet, watching youtube video’s, reading forums. Searching any site I could find that had anything to do with airguns in general.

I soon discovered air gun technology has come a long way since the days of my youth. You see in the 70’s as far as I knew. A Benjamin pump air rifle was the best air gun anyone would ever need. Since at the time I lived in a small farm town and the only reference tools I had was a Sear’s or Montgomery Wards catalog.

After much thought and research, I decided to buy the basic Benjamin Armada since it is a Benjamin Marauder dressed in AR15 clothing. I wanted to buy all the Armada accessories separately to suite my needs.

The Benjamin Marauder has been in production since around 2010. Second generation Marauders have been shipping for a while now and they have a large following with incredible aftermarket support and parts availability. The .25 cal rifles have a Green Mountain barrel that are known to be extremely accurate.

The image above is of 24 rounds shot from 25 yards with a Green Mountain Barrel.

Pulling the trigger

Full disclaimer: I make a few pennies if you purchase using the Amazon links on APG – I gotta support this habit and site somehow 🙂

All items were purchased on Amazon except some of the pellets (I have Amazon Prime and love that fast free shipping)

Here is my current setup:

Benjamin Armada 25 Cal Rifle

UTG 3-12X44 30mm Compact Scope

CVLIFE 6- 9 Inches Tactical Rifle Bipod

Offset Cree Bulb flashlight with remote on/off and momentary press remote (You will need a 18650 Li-ion battery and charger for this).

2 Extra 8 round Benjamin magazines

2800 JSB Exact Kings Diablo .25 350 Pellet per tin (Best deal = Pyramid air or Airgun Depot – buy 3 get one free as of this writing)

Hill Pump MK4 that can pump up to 4000 psi (3000 psi max is recommend for this rifle)

I spent close to a grand to get to this point, but I researched and bought the best items I could find for the price. There are cheaper PCP pumps, and scopes et al. So I bet a person could work harder at finding other accessories and refurbished or used items to bring the total cost down.

Next after reading about tuning the Marauder to get a higher shot count or more power and less shots at the marauderairrifles.com forum. I had to buy a chronograph and then jumped right down the rabbit hole known as “acquiring the perfect tune”.

For the adjustment process you need a Chronograph. I went for the Caldwell “Ballistic Precision Chronograph” since I could hook it up to my phone with a simple audio cable provided with the purchase, and keep records of my Chrono groups. Then email them to myself for future reference. Plus it was cheaper then the other models and had pretty good reviews. Don’t use this Chrono under florescent lights or you will get horrible results. The readings will really go sideways if you have a flashlight on your gun and use it at night. I used an incandescent light aimed straight down on the unit and didn’t get too many errors during the session depicted in the image above. I have a full time job, so I had to figure out how to shoot at night. Ode to the joy of owning a moderated air gun. I can shoot it out my back bedroom door at night. And its so quiet my wife cant hear it in the front of the house, neither can my neighbors – or the police!

Coming soon:
Tuning the Stock Armada for hand pump users
Going from a Hill MK4 pump to a 75cf tank fill station, and getting it filled in a remote town