Calling all 25 cal marauder REGULATED guns

[rsterne]

You hear shorty and I using the terms "plateau", "knee" and "downslope", so for those who don't know what we mean, I'll explain.... For a given pressure, as you increase hammer strike (usually preload) you tend to get more velocity.... However, that doesn't keep on forever, eventually no matter how hard you hit the valve you won't get any more power.... If you plot out velocity vs. preload, you get a curve like this....



Note that past about 4 turns of preload the velocity "plateaus", ie it doesn't keep increasing, but the efficiency keeps dropping and the gun becomes an "air-hog".... When the preload is less than at 5 turns, the velocity is decreasing, ie it is on a "downslope", and the less preload the lower the velocity.... Between 4 and 5 turns is what we call the "knee" of the curve.... In that region you are getting nearly all of the velocity possible, but you will notice that the efficiency is still increasing.... It makes sense that is a good place to tune the gun, and it is.... There is another set of characteristics that tie in with this, shown in the graph below.... This doesn't represent any particular PCP, it's "generic", and the FPE/CI numbers I will use below are "invented" to fit the description....



The PCP represented is regulated at 1500 psi.... It shows what typically happens to the velocity as the pressure decreases from a full tank (3000 psi) down to, and beyond, the 1500 psi setpoint.... What isn't shown is the shot count.... On the plateau (blue line) you might only be getting 0.8 FPE/CI, and get, let's say 20 shots.... When tuned on the knee (orange line) the efficiency will be much higher, maybe 1.2 FPE/CI, plus you can shoot a bit below the setpoint, so you might get 32-36 shots.... If you tune on the downslope (the grey line), your efficiency might be 1.6 FPE/CI, and you might get 50 shots above 1500 psi (at much lower FPE), but then the velocity will start increasing, just as if the gun wasn't regulated (because it isn't any more).... Think of it as an unregulated PCP tuned for 1200 psi, but where the top part of the curve is constant velocity (because of the constant pressure delivered by the regulator)....

I hope this helps you understand the terminology, and also what happens when you tune for different parts of the envelope.... I hope shorty didn't mind the diversion, just trying to help....

Bob

[shorty]

Don't mind one bit Bob. I kind of thought at first you were looking for reg sizing to calculate efficiency because it's pretty un heard of for 1.7+ efficiency on a 25 PCP.

Anyway,
Not sure if we are gonna get anymore regulated 25 cal marauder shot tunes or not but, I want to lay this out there if this or any other posts of regulating your 25 cal Mrod has you on the fence.

Cost:
My gun was was 399 with the gander mountain sale a couple months ago.The reg cost 120. I did the work myself and yes I do have a lathe. BUT, from what we have learned, I think this might work too.
Gen 2 marauder or Armada, 5 dollar drill bit at .161"/.165" (to drill out the exit port and barrel - or aftermarket valve 100/150 bucks), a matching transfer port sleeve, a short stiff spring or SSG (homemade or bought 70 bucks or so) and the Huma reg for 120.

For a 4040 tune (I really like that term) a reg set point between 1900/2100 psi.

1 or 2 hrs of work depending on if you make the stuff yourself or purchase all drop in parts.

Not sure what a tuner such as Motorhead would charge (and this should be discussed only between you and him or who-ever) but, from this and a few other posts, it seems like you should expect nothing less than a 4040 tune from one of the pros when getting your 25 cal Mrod regulated.

I gotta tell you though,
There's nothing like a 4040 tune or a 24/50 tune using this 25 Mrod. I truly hated filling after every 16 to 28 shots to keep it under 4% ES. Too me, this is how a PCP should respond. It was worth the 120 bucks to get 50%+ more shots with a low ES. Let's face it, 35 FPE to 50 FPE is a great power level for the available pellet weights in 25 cal.

[Ozarkairgunner]

I'll be sure to let you know how mine turns out once the reg makes it in and I have some time to work it over, hopefully this weekend maybe.
Also I want to point out I got my Huma reg from the Netherlands and it only cost me $109 shipped, not much of a difference, but might be cheaper or more depending on where you have it shipped to.

[shorty]

Sounds good. Can't wait to hear.

Hey Dairyboy,
Did you get it squared away yet?

[Dairyboy]

Lol getting there should have the hammer situation figured out tonight and hopefully run a string tomorrow. Dang responsibilities keep getting in the way of my toys

[Ozarkairgunner]

Okay guys, maybe you can clarify this for me. With the newer huma reg that has the gauge block built in there doesn't seem to be much wiggle room for pleume, without drilling it out and modifying it anyway, and I don't plan on it. But with this design is the gauge assembly itself enough to hold the regulator where it needs to be or will I need to plan on pinning it?

[FuzzyGrub]

Okay guys, maybe you can clarify this for me. With the newer huma reg that has the gauge block built in there doesn't seem to be much wiggle room for pleume, without drilling it out and modifying it anyway, and I don't plan on it. But with this design is the gauge assembly itself enough to hold the regulator where it needs to be or will I need to plan on pinning it?

If you are meaning that you will use the other style huma, to get a larger plenum, that seals against the gauge block, you do not need to pin it.  The gauge block is butted up against the valve.  With that style, you will want to hog out the gauge block or buy one like Tim Hill's. 

[Ozarkairgunner]

No, I bought the newer one. I should remove the original gauge block completely and this reg has the gauge port made in.

[FuzzyGrub]

No, I bought the newer one. I should remove the original gauge block completely and this reg has the gauge port made in.

That just butts up against the valve.  No pins needed.   

[Ozarkairgunner]

Awesome, thanks, I didn't know if there was any gap anywhere

[shorty]

Yo Dillion,
Where's that 25 cal regulated shot string. Just busting chops!!!!!

I have been waiting for it so that I can post this pic. For holloween we went to the agriculture center cause they had something going on there and this old school carrige was there.
All I could think about was you. Do you run Moooo cows or meat cows? 

[FuzzyGrub]

So we have some excellent examples using an aftermarket performance valve, and a heavily modified oem using a lathe.  So, I'm working on the DIY version.  ie valve mods that can be done by most DIYers with a drill press.  So I modified my stock valve today.  See changes below:

Mrod 25 cal Valve

Part                  Original   Modified   % Increase Inlet Diameter   0.2500   0.2813    Inlet Area   0.0491   0.0621   26.5625           Valve Body Diameter   0.4219   0.5000    Valve Body Area           0.1398   0.1963   40.4664           Stem Diameter           0.1250   0.1250    Stem Area                   0.0123   0.0123   0.0000           Pocket Diameter           0.2000   0.2250    Pocket Area           0.0314   0.0398    Pocket Area - Stem   0.0191   0.0275   43.5897           Exhaust Diameter   0.1400   0.1650    Exhaust Area           0.0154   0.0214   38.9031           TP Diameter           0.1400   0.1600    TP Area                   0.0154   0.0201   30.6122           Barrel Port Diameter   0.1400   0.1600    Barrel Port Area           0.0154   0.0201   30.6122 Now, I consider the pocket, exhaust, TP, and barrel port the key flow mods.  The rest just add some slight plenum increase.          Of note: Normally, I'd go with more inlet cap mod and a light conical spring, with a LW hammer.  I only have the oem hammer for now, so will wait on the spring associated mods. I have to finish the DIY SGG and re-assemble, but should have results sometime this weekend.

[Dairyboy]

Yo Dillion,
Where's that 25 cal regulated shot string. Just busting chops!!!!!

I have been waiting for it so that I can post this pic. For holloween we went to the agriculture center cause they had something going on there and this old school carrige was there.
All I could think about was you. Do you run Moooo cows or meat cows? 

Lol should be ready for testing tomorrow during my lunch break! Been working last 12 days straight and won't get a day off until next Sunday. Normally do all my tuning on Sundays which are my normal day offs but since I haven't had one been tough finding time for any of it.

That is a really cool Dairy cart there. I guess we would raise what you call moo cows. 

[Dairyboy]

So today I finally decided to pull the whole gun apart and figure out why I can't figure it out. So this regulator is the first kind without a pressure gauge. I have a hogged out one I will be installing. Also the regulator was set at 2400psi...way too high for what I wanted. So now backed it down to 1900ish goin back together and hopefully will work this time

[FuzzyGrub]

My first string showed that I was at the power I want (865fps) but not the shot count.  Only got about 16 shots before going off reg.   Reg is set at 2.2Kpsi.   Turned out I was way up on the plateu, some adjustment and shortening the 3" spring by 1/4" got me closer to the knee, at 850fps.   I'm at 26 shots before going off reg, then it is a steady decline. 

Shot   FPS   3.2K Fill   25.4g Kings
1   852      
2   853      
3   855      
4   857      
5   854      
6   853      
7   855      
8   857      
9   855      
10   853      
11   851      
12   853      
13   854      
14   854      
15   855      
16   852      
17   850      
18   852      
19   850      
20   850      
21   849      
22   849      
23   851      
24   853      
25   853      
26   850      
27   847      
28   846      
29   843      
30   838      
31   836      
32   835      


Still a far cry from PBguns results.  I need to go to a lighter hammer, and will open exhaust and TP some more to 0.170". 

[Dairyboy]

Finally got the gun back together and only had time for a few shots. Gauge is showing 1950~ psi and with a Hill valve and a light valve spring and a hill gauge port .162 TP, .187 barrel port and 22" TJs with Rocker1 LW hammer (28grams) on a WAR SSG with not much spring tension I'm getting 875fps avg that was only about 8 shots for what I had time to test and couldn't run full string. The shot cycle is super short and snappy I'm very happy with it

[PBguns]

My first string showed that I was at the power I want (865fps) but not the shot count.  Only got about 16 shots before going off reg.   Reg is set at 2.2Kpsi.   Turned out I was way up on the plateu, some adjustment and shortening the 3" spring by 1/4" got me closer to the knee, at 850fps.   I'm at 26 shots before going off reg, then it is a steady decline. 

Shot   FPS   3.2K Fill   25.4g Kings
1   852      
2   853      
3   855      
4   857      
5   854      
6   853      
7   855      
8   857      
9   855      
10   853      
11   851      
12   853      
13   854      
14   854      
15   855      
16   852      
17   850      
18   852      
19   850      
20   850      
21   849      
22   849      
23   851      
24   853      
25   853      
26   850      
27   847      
28   846      
29   843      
30   838      
31   836      
32   835      


Still a far cry from PBguns results.  I need to go to a lighter hammer, and will open exhaust and TP some more to 0.170". 

I think you'r headed straight towards the tune your after! Nice to see it come together.

[Dairyboy]

48 shots from 865-830 fps. 40 shots on regulation around 853fps avg with 25.39 JSB kings. I'm done tuning!

[Sfttailrdr46]

Nicely done 

[PBguns]

48 shots from 865-830 fps. 40 shots on regulation around 853fps avg with 25.39 JSB kings. I'm done tuning!

Welcome to the club! Good work! So how many in the 40/40 (no res) club now is it 3?