How To Improve Unregulated Marauders - Add 100 FPS Or Double The Shot Count.

[hardairmag]

Spending some "quality lockdown time" with my old Marauder, I was reminded of the air puff in the face every time I pulled the trigger. So I decided to do something about it and the project grew into something else - a way to make a significant improvement in performance!

First, I blocked the hammer spring adjustment hole with my thumb. That stopped the puff of air but the muzzle velocity fell - which was definitely NOT what I wanted. So, I ended-up doing some full-scale shootdown testing and found some surprising results. Yes, blocking the hammer spring adjustment hole reduced muzzle velocity, but it also lead to a much flatter shot curve. Something like a "regulator lite" effect.

With a flatter shot curve, I was able to give the gun a more aggressive tune, ending-up with more power, more shots, or both. Then a ton of testing with unregulated Marauders in all three calibers proved that it works every time with no less than 12 combinations of gun and pellets. But a little different with every individual gun/pellet combination. Here's some examples...

In .177 cal, the result was double the number of consistent shots - in fact more, as you can see above. The next graph shows that much increased FPS (and power) was achieved in .22 caliber - over a 25% increase in FPS over 30 shots.

Even the .25 cal Marauder gained up to 10% in power and shot count - as well as eliminating that pesky air puff in the face. And in no case is it necessary to make any change to the gun which could invalidate the factory warranty or requires dismantling the gun - beyond removing the stock, that is.

You can see more detail and a ton of test results in Hard Air Magazine. Plus, I've put together a simple, low cost kit that enables anyone with an unregulated Marauder air rifle to achieve similar results for themselves - even without a Chronograph. It's an ideal lockdown project!

https://hardairmagazine.com/ham-columns/benjamin-marauder-tune-kit-can-add-100-fps-or-double-shot-count/

https://hardairmagazine.com/ham-columns/more-test-results-for-benjamin-marauder-and-armada-tune-kit/

https://hardairmagazine.com/ham-columns/theory-of-operation-for-the-benjamin-marauder-tune-kit/

Have fun

 

[BlackICE]

You're getting a puff of air in your face you have a leak somewhere. Probably the valve stem. Marauder valve stems don't have any seals on them they're counting on a very close fit to limit the air leakage. However steel rubbing on aluminum is not a great bearing surface with many shots I would suspect though it leaks more and more air.

 

[Yo]

Very interesting... Yo!

 

[hardairmag]

Thanks both for your comments!

BlackICE, current thinking on the source of the air puff in the face is that it's actually NOT due to a leak. All seven guns I tested during this development showed similar behavior and none of them is a leaker.

I agree that there's very likely to be some air leakage around the valve stem. This would apply at any PCP air rifle, of course.

However, it's most likely that the major cause of the air puff is hammer bounce. The Marauder hammer has a strong tendency to bounce back on firing. In fact this phenomenon has been used by the current Crosman design team in developing the blowback action in the new SAM (Semi Auto Marauder).

It's likely that the strength of the hammer bounce, together with the relative tightness of the hammer fit inside the HPA tube, is the cause of the puff. Air sucks into the rear of the tube as the hammer flies forward on firing and is then pushed back out by the bounce (or more likely multiple bounces).

So - in fact - my "tube plug" idea probably is actually functioning as a type of hammer de-bounce device.

At least, that's the thinking. Without the benefit of some pretty expensive high speed photography, it's difficult to prove this, however.

One thing's for certain. Whatever the real cause, benefits have been found from my idea on every Marauder unregulated I've tested so far!

Stephen Archer

Hard Air Magazine

 

[profsrgary]

I have my Mrod Gen 2 set to shoot 14.3 grain pellets at 820 to 845 fps. NO air in the face at all 50 shots between 1600 1nd 2450 psi. Hammer tension 1.5 turns cw and and a stroke set at 3 turns cw. This set up shoots deadly accurate. With the factory settings I had a slight amount of air in the face at times and pellet velocity about 20 fps faster but this set up works great for me but probably not as well if I up the pellet weight and fill pressure. Thanks for your post though as I may up pellet weight or velocity some time and give your suggestion a try.

 

[FuzzyGrub]

To me, this just highlights how bad the stock tunes are. Bad tunes can have more hammer bounce. Plugging the back just forces any air in/out the hammer pin slot and the trigger sear slot. 

IMO: Put the $20 toward a chrony and spend the time learning how to tune it. Don't want to tune? Buy a regulated gun at the power you need.

 

[Guest]

Nice study. Thanks for the great information.

 

[JamesD.]

In Crosman’s prototype valves there was an internal O-ring gland cut to fit around valve stem in the valve body. Those gave a ton of shots.

I’m gonna try your plug; but I also want to add a .22 23.75” LW Poly and a no choke barrel for slugs as this short barrel & bull pup thing isn’t what everyone wants. 


I still say a Marauder is a great platform for reasonable power and even lightweight slugs. 
Thanks for the research.

 

[Superlag]

Edit: Just read about your theory about hammer bounce back being the cause of the puff of air. That makes sense. I limited tuning to a certain number of combinations of spring tension and hammer throw and picked the lowest standard deviation combination so that might have minimized my hammer bounce back and thus eliminated the possible puff of air one could have experienced.

I've never gotten a puffs of air in the face with my .22 Gen 2 MRod, that sounds like a defect, but did tune mine to shoot 18.13 JSBs at 880fps. Have a post on here about my results and tuning methods. Here are my final numbers, as the stock tune, as said above by many, is no where near as good as it can get.

 

[rickgomez2003]

I will have to test mine before i upgrade everything in my Marauder.