Benjamin Marauder .22 Modding & Tunning Results

[rjorge]

After modding my father in laws Gen 1 Marauder, the best shot string I got was 30 shots within 4% and 25 within 2% @ 848 fps average with 18 gr JSBs from 3000 to 2250 psi. Although that string had an efficiency of 1.15 FPE/Ci, I knew I could extend the shot string with a regulator while having a better ES as well. I instructed him to get a Huma regulator for a .25 cal, as I knew I needed 25-30 cc of total plenum volume in order to achieve my goal of 40 shots @ 30 FPE.

Turns out the Huma regulator plenum volume is 15cc, which is the same as the Hatsan .25 cal regulator btw. Now all I needed to do was to make sure I got at least another 10-15 cc from the valve and gauge block volumes.

Since I had already changed all the ports to .166", valve throat at .215", and bored the valve and gauge block for easier flow into the valve, I decided to revisit the valve to squeeze a little more efficiency and better flow. I began by boring the valve while keeping in mind the front breech screws. I resurfaced the valve throat with an end mill and polished it with 1000-1500-Polishing compound in order to get a nice sealing surface for the new peek poppet seal; I made it with a 45 degree/.012" sealing surface. It sealed on the first try at under 1000 psi. The spring holder is pressed in. I also removed material from the end of the valve and shortened the gauge block by using a smaller o-ring and eliminating the other o-ring groove. A new transfer port was made out of SS as well. A will be making a new degassing tool with 1/2-20 threads instead.









Since the valve would no longer bear the force from the regulator pressing against the gauge block, I made a spacer to eliminate the gap between the gauge threads and tube. After some calculations, the steel screw and spacer can easily handle the force from the regulator.



Another goal was to eliminate hammer bounce as much as possible. One way to accomplish this is to use a stiff spring, in this case 17 lbs./in, and a gap between the end of the spring and the hammer. I left a gap of .050", this allows the hammer to fully stop after the initial hit against the valve instead of compressing the spring and reopening the valve multiple times. I also removed some material from the hammer, as 79 gr is a bit much for only 30 FPE. I had to keep a close eye on the balance of hammer weight and no spring preload, since I could easily over/undershoot my 880 fps goal with 18 gr JSBs. I modified the end cap containing the spring preload adjustment by threading it 1/2-20 all the way through. This is to move the preload screw further back and allow the spring to have no tension at 0 preload. A set screw was added to lock the preload in place.









The total plenum volume was measured: 9 cc from the valve + 7 cc from gauge block & volume between it and the valve + 15 cc from the regulator, which equals to 31 cubic centimeters. The total volume between the regulator and the end of fill probe block is 188.7 cc, so I only lost 26.3 cc due to the regulator.

I set the regulator at 110 BAR and filled the cylinder to 3000 psi. I set the spring preload at 0, which allows the spring to move back and forth ~ .05". The first shot was 900 fps! Since no 2 shot strings are alike, I won't spend the time typing all 44 shots. I still have to notch the screw that slows the air flow into the regulator to improve recharging times, but the ES was right around 10 fps. I did not wait long between shots.

So 44 shots averaging 902 fps from 3000 psi to roughly 1500 psi = 1.2 FPE/Ci, which in my opinion is great given the short Marauder barrel. I may lighten the hammer a hair to decrease the velocity to 880 and possibly get 5 magazines.

I have shot many sub 1/2" groups at 50 yards with this Marauder, so I know accuracy could only get better! It's barrel is somewhat pellet picky though, it's best groups only comes from 18 gr JSBs.

I believe in giving credit where is due, where I first learned:
Peek poppet: SeanMP
Spring gap as anti hammer debounce: lloyd-ss and rsterne
Optimum regulated plenum sizes: rsterne
Optimum port sizes: rsterne
Lighter hammer approach: Motorhead
 
Thank you for sharing the information with us all!
I probably missed a couple that I will add as I think about it!

[Motorhead]

Some very unique mods going on there ... well done !

FYI ... still have a couple @26 gram LW hammers for regulated m-rods ... PM if interested.

[moorepower]

What are you using for a valve spring?

[rjorge]

Thank you, Scott. I'm thinking a hammer weight around 45 g would bring the velocity down to 880. I wish I had the time to do the same thing you did to arrive at the 28 g, where you slowly increased the hammer weight to find the velocity plateou @ 0 preload with the stock spring.

What are you using for a valve spring?

The hammer spring is from McMaster Carr, part # 1986K19. The valve poppet spring is one I had lying around, not sure on the specs. It is lighter than the stock spring though.

[Motorhead]

Thank you, Scott. I'm thinking a hammer weight around 45 g would bring the velocity down to 880. I wish I had the time to do the same thing you did to arrive at the 28 g, where you slowly increased the hammer weight to find the velocity plateou @ 0 preload with the stock spring.

What are you using for a valve spring?

The hammer spring is from McMaster Carr, part # 1986K19. The valve poppet spring is one I had lying around, not sure on the specs. It is lighter than the stock spring though.

The research has already been done ... at 1.8 to 2k working pressure on poppets of +/- .300/.350" diameters and a light poppet spring ( Given ample transfer size *you have  )  weight from 25 to 35 grams is all required.
More weight generally just increases dwell time and uses more air.

Make a hammer 30 grams give or take and you will make the power you seek IMO w/o issue.

*** As reference my own .22 m-rod can muster 32 ft lbs on a 26 gram hammer on .165" transfer, stock hammer spring at full stroke travel.   While getting 40 + 10 off reg shots at 30 ft lbs power.

The BAM 50 in .25 cal makes 50 ft lbs on a 30 gram hammer on .200 transfer.

The RAW TM with a .22 barrel makes 32 ft lbs on a 22 gram hammer on .165 transfer ( Tho heavy hammer spring )

Try it ... you may be enlightened 

[FuzzyGrub]

WOW, excellent work!  You got allot out of that valve.  I'm just starting a 22 mrod reg project and haven't seen the extent of the mods you have done, before.   Thx for sharing.

[cilami]

After reading this thread, I would like to ask what performance level could be achieved doing these, or similar, mods/tunning to a regulated Prod? I recently got a HUMA regulator for my Prod. For example, would it be possible to get 16 shots at 22 fpe within 1-2% ES?

There is a shot string, posted at the HUMA website, of 31 shots @ 18.8 fpe, for a total of 582.8 fpe. That seems to be huge for a Prod! So far I have not been able to duplicate that... but keep trying hard. See here:

http://huma-air.com/wp-content/uploads/2015/06/shotstring-Prod-124-bar.pdf

[npunk42]

Good work. That machine shop is not wasted on you.

[rjorge]

Scott, I see some major differences between your Mrod and this one. The stock Mrod at full stroke (adjustment screw backed all the way) has around 3/8" or more of preload on the spring, on "my" Mrod the stock spring adds 0" of preload to the spring. To give you an idea, the stock spring @ 0 preload (.05" of negative preload) with the 49g hammer shot 18 gr JSBs at 365 fps! We are trying to achieve the same thing, but with different approaches. Light hammer + preload = heavier hammer + less preload. I believe both can achieve exactly the same lift and dwell, but hammer bounce behaves differently. I achieved 902 fps avg for 44 shots @ 1.21 FPE/Ci while you achieved 870 fps avg for 51 shots @ 1.05 FPE/Ci (based on Bobs calculations), so I would say that I could achieve the same number of shots at the same velocity by either further decreasing the preload, reducing the hammer weight slightly or using a slightly lighter spring. I will try to decrease the preload first, since it is the easiest approach.

cilami, I'm not sure of the specs on the prod. I would start with a 20-22 cc plenum while maximizing the unregulated cylinder volume.

Thanks FuzzyGrub & npunk42! I'm hoping to upgrade my lathe soon, the spindle bore is tiny on these Sherlines!

[Motorhead]

Indeed the efficiency numbers seem to be biased in your way ...
That said "LOCK TIME" which is very important for competitive shooter go's to the lighter & faster hammer configuration. As is shot cycle vibration far less with a light hammer/striker.

BOTH ways may indeed function similar getting pellet down range with consistency, but take into account the other peripheral cause & effects happening they become very different indeed.

It's all fun stuff and more so as other approaches get explored 

keep up the good work 

[rjorge]

That said "LOCK TIME" which is very important for competitive shooter go's to the lighter & faster hammer configuration. As is shot cycle vibration far less with a light hammer/striker.

I agree with you on this one, I'd say the lock time on my set up is pushing close to 10 ms.

Yes, It's all fun stuff and more so as other approaches get explored  For me, this is what has kept this hobby going longer than any other!

[RayK]

Nice work!  You're ready to turn pro and start RJorge Airgun Tuning Service.

Ray

[Motorhead]

Here a FUN project for you ....



Hammer design that allows Stroke changing WITH OUT it changing spring preload.
Inner barrel which is also the spring cup moves independent of the outside sleeve which gets held by trigger sear.
* sadly I only made one and it was quite the challenge getting the threading fit right to it would be adjustable, but snug enough to not move under use.  * The rifle this was in got sold while i forgot "THIS" hammer was in place ... Big mistake on my part !!   Was really killer hammer that exceeded my expectations.


See: http://www.gatewaytoairguns.org/GTA/index.php?topic=39439.0

** Years later, it occurs to me the Core/ spring cup could be Aluminum, Steel or Brass for weighting differences while keeping the self lubricating MDS nylon outer sleeve.