44.5 fpe 32 shots unregulated .25 Mrod

[Ozarkairgunner]

Okay this will be a slightly longer post than usual for me and I plan on putting up some graphics later, but for now I hope just a shot strings will work for y'all. I have a Gen 1 .25 Benjamin Marauder that I wanted to get the most usable shot I could out of it without having to dump much cash into it (I'm cheap). I was a little worried about it at first, expecially when I had first started this folks were saying not to regulate a  .25 and that they were only getting 16-24 decent shots. By decent I assume most people meant something in the 40-50fpe range, that's what I was aiming for anyway. So after I bought my Mrod, and a few others lol, this past spring I just shot it like it was while I did some more research on the SSG, other tuning processes, and waiting for my crony to come in. Once the crony had arrived I was still shooting the benj domes, simply because that was the only .25 pellet I could buy at the store and what I had available. I won't list the shot strings from that but after a few tweets with hammer spring preload and the valve metering screw I was able to get 32 shots for 3k down to 1900psi, I have to say I had a major power curve with slight over 50fps extreme spread, but at the time I was hand pumping and I wanted the most shots I could get. So I settled for that for a few months, that is until this past weekend anyway. Since my first attempt at a tune I've had some time to play with a few other projects, picked up a 30min CF tank and fill assembly, and find some better pellets for my rifle. I've now narrowed it down to 2 depending on what I'm doing, Predator Polymag seems to be great hunting pellets and I get amazing accuracy out of them but I believe the heavy JSB MK2 33.9 slightly out preformed the polymags and with the added weight and higher BC I decided they would be my pellet to tune with. So first I shot a string with the rifle as it was to get a solid baseline and use the same pellets throughout the tuning process, first string with no mods other than tune runs as follows: (all strings start at 3k off of tank and go down to around 1900psi and #s listed are in fps using JSB 33.9 pellets)
1. 692       9. 701       17. 728         25. 721
2. 692     10. 711       18. 731         26. 721
3. 696     11. 711       19. 728         27. 722
4. 701     12. 722       20. 729         28. 715
5. 694     13. 712       21. 734         29. 706
6. 692     14. 719       22. 728         30. 702
7. 700     15.722        23. 726          31. 695
8. 711     16. 727       24. 721          32. 693
That's an average for 711fps/ 38fpe.
Okay next step was to build and assemble my SSG. Again I plan on posting pics later, sorry guys but I hope you can follow this. Again I'm cheap so I make what I can, my SSG is very simple and straightforward, not the best but it does its job wonderfully. I used the same cold rolled 3/16" steel rod that I used making an SSG for my Disco and an HPA 2240 conversion I did. I cut a section around 4" to give me some room to play with and tapped one end for a 10-32 nut. After a quick check I found that I wouldn't need to trim the edges off the nut as I had done for the Disco and 2240 hammers. What I did end up needing to do was take a flat washer and trim it down to fit inside the hammer placed on the top of the 10-32 nut giving the spring a solid flat to rest on top of. I should note that I did not modify my hammer at all and the hammer stroke fully in snug against the hammer so as the end of the 3/16" rod was slightly tapered down to fit inside the hex head and keep things centered. Also using the 3/16 rod there is no need and drilling through the spring preload screw and the rod passes through with ease. The preload was set flush to the inside of the end cap towards the hammer, sorry I don't have the # of turns and so on. Hope that made sense to everyone. So once I had all that together it was time to run another string and see if any changes had occurred, and they had, before I adjusted anything else. Shot strings with SSG installed and no other changes is as follows.
1. 739      9. 753     17. 744      25. 744
2. 752    10. 749     18. 747      26. 735
3. 741    11. 746     19. 752       27. 747
4. 746    12. 749      20. 748      28. 747
5. 746    13. 751      21. 746      29. 739
6. 747    14. 760      22. 754      30. 736
7. 747    15. 751      23. 757      31. 728
8. 740    16. 750      24. 749      32. 735
Needless to say I was happy from the start that it worked this well already but I felt like I could squeeze a bit more out of it. So after a few minor adjustments to the SSG gap and preload and opening the valve metering screw a bit more and I hit my wall between shot count and power. My final string looks like this for the moment.
1. 754      9. 768      17. 786       25. 772
2. 753    10. 778      18. 782       26. 767
3. 753    11. 777      19. 770       27. 775
4. 765    12. 773      20. 774       28. 766
5. 756    13. 776      21. 782       29. 765
6. 768    14. 778      22. 768       30. 755
7. 761    15. 776      23. 781        31. 755
8. 771     16. 782     24. 770        32. 755
This gives me a final average of 769fps/44.5fpe with the heavy pellets. I did shoot a few polymags thru the crony just to get a basic idea and it looks like they'll be averaging in the ballpark of 840ish fps. Well I suppose that's about it for now, please let me know what y'all think and if you have any suggestions or questions I'll be more than happy to listen and or try to answer what I can. Also I do have the new Huma regulator with the gauge port ordered and on the way, should be here this weekend I think, and hopefully I'll be able to get a few more shots out and a flatter shot strings. Enjoy and look forward to some feedback.

[Dairyboy]

That's very impressive great work!!

[45Bravo]

Cool.

[Tater]

Very nice job C.J., great shot string.

[rsterne]

If you are using a stock MRod reservoir, and filling to 3000 psi, we can calculate your efficiency.... You are getting 32 shots averaging 44.5 FPE = 1424 FPE.... The reservoir is 215 cc (13.1 CI) and your pressure drop is (3000-1900) / 1.45 = 75.9 bar, for a total volume of (13.1 x 75.9) = 994 CI.... The efficiency is therefore (1424 / 994) = 1.43 FPE/CI.... I would say that is great efficiency at that FPE level.... Congratulations....

Bob

[oldpro]

Not bad not bad at all! Good work.

[Ozarkairgunner]

Thank you for all the kind words, I wish I could take full credit for all this but I know that part of it was lucky in having a good rifle to build off of and the weath of knowledge from people on the forum that helped me get to where I'm at on here. Bob, you make the #s look easy, wish I knew all the formulas to get there, also what graphing charts are y'all using so I can download them as well?

[45Bravo]

We are fortunate to have Bob, I am glad he enjoys crunching numbers..

Math?
Not my thing.

I just shoot it, does it get more shots than before, at the same speed?

Then I'm good..

He is a great resource, we give him the numbers, he boils it down into the data we need.

Thanks again Bob..

[Ozarkairgunner]

Yes he is, with any luck maybe I'll be able to meet him one day and convince him to sit down and school me on a few things, I feel like I could get it if explained. Just when I start reading it on here it can get tricky because of wording, and I'm not the world's best at trying to explain or ask the parts I don't understand. Also, it's always cool to meet other ag shooters, expecially someone as knowledgeable as Bob, or even you Ian lol.

[n2omike]

Amazing numbers!  Your SSG seems to work VERY well! 

Mine is a stock .25 that I have resisted tearing apart so far...  Kind of waiting for it to screw up, where I have to take it apart, anyway.  lol  Gun is deadly consistent and accurate through 3 mags.  Starts to drop a little bit if you push the 4th.  Plenty of power to absolutely destroy birds. 

Anyway...  Might be handy for those wanting to practically tune their stock guns.

Settings: Hp = 5T, Ht = 3.5T, V = 4T

JSB Kings on a 3.2K fill

Tried this, and got a nice shot string at around 800fps!  3200 to 1800 psi

783
788
790
791
793
792
791
794   8
788
793
792
801
801
800
795
795   16
794
789
787
794
790
787
E
781   24
771
771
768
757
758
747
744
734   32

Straight out of the box...   it shot a tad bit faster, but couldn't even get 2 mags before it fell off the cliff.
Starting 3100 psi, ending 2000 psi.

1.  835
2.  840
3.  841
4.  838
5.  839
6.  828
7.  833
8.  830
9.  821
10. 820
11. 814
12. 809
13. 804
14. 798
15. 795
16. 780

[Ozarkairgunner]

Very nice

[n2omike]

Okay next step was to build and assemble my SSG. Again I plan on posting pics later, sorry guys but I hope you can follow this. Again I'm cheap so I make what I can, my SSG is very simple and straightforward, not the best but it does its job wonderfully. I used the same cold rolled 3/16" steel rod that I used making an SSG for my Disco......

As for your SSG...

Did you make a longer one that sticks out the back, or did you try to cram it all inside?

I have some theories...   Curious what you did...

Thanks!

[Jesse]

Nice!

[Ozarkairgunner]

This was my first attempt at the SSG on my Mrod, I plan on redoing it fairly soon, I will shorten the shaft a bit and not tap as far down. I gave myself plenty of wiggle room on this one to find all my measuring points to make one a bit more aesthetically pleasing as well as functional. In addition I will most likely back the set nuts up to allow for an additional washer at the back cushioned with a fat O-ring. One thing I will note that I thought was pretty cool, this also seemed to really reduce the "ping" noise that you would hear in the air reservoir. The next time I open it up to put in my regulator I will be getting more precise measurements of everything for those that are interested.

[jward681]

CJ excellent work and return on your time building the SSG! Looking forward to seeing what the HUMA adds to the equation for you.

With many of the recent build posts lately on 22xx's, QBs, Mrods and so on y'all have made it nearly impossible to decide what to do for my next rifle....dang you GTA!!! 

John

[screwwork]

Excellent  job on the tuning the Mrod and custom SSG CJ, do happen to know what the spring spec's are for the spring you used?
Thanks Randy

[Geoff]

some very nice strings there.  I may look into a 25cal at some point, though unless I start hunting I cannot justify one.

[Ozarkairgunner]

Thanks guys, as for the specs I plan on posting them hopefully this weekend when I take the gun apart to put in my regulator in. I'll write everything down in the event I have any problems I'll go right back to where I'm at now.