My first try at tuning the .22 Mrod

[mb4859]

Let me set the stage.  I am using my new ProChrono Digital and it didn't miss a shot...
The pellets are H&N target 21.14 gr..  The first string I filled to 3100 psi on the pump.
2900 on the gun and shot down to 1900 psi.
1.  789      21. 836
2.  788      22. 837
3.  806      23. 837
4.  796      24. 842
5.  805      25. 849
6.  809      26. 846
7.  800      27. 839
8.  814      28. 836
9.  809      29. 838
10. 820      30. 836
11. 819      31. 840
12. 822      32. 834
13. 822      33. 826
14. 819      34. 830
15. 823      35. 823
16. 823      36. 822
17. 824      37. 819
18. 826      38. 818
19. 835      39. 803
20. 833      40. 803

[mb4859]

Forgot to list these.
Spring screw in 3 turns CW
Throw in 1/2 CW
 Valve screw out 4-1/2 CCW from closed

[wimpanzee]

Seems to me you could lower the fill pressure, and shoot it down a bit further to finish out the bell curve - still get 20 shots, but with less extreme spread.

[npunk42]

From your first shot to your highest velocity, are the 21gr pellets hitting the bullseye? If so, leave it and have fun. If not, you still have some work to do to find what FPS those pellets like to fly at. Then tune to get more shots in that range.

[mb4859]

I didn't shot these pellets for accuracy, just looking at the fps.  I probably should have.

[wormbobskey]

None of it makes any sense if you can't hit what your aiming at. You shot 20 shots then refilled the rifle, right?

[mb4859]

No I shot all 40 shots on one fill from 2900 to 1900 psi.

[npunk42]

That's the beauty thing about the Marauder, you can tune this way and that, more power, efficiency, whatever. If you get a hankering to tune again, try the A Teams B Tune as described at the other site. It worked well for me, I have just been fine tuning from those results since then.

[HillGSA]

Let me set the stage.  I am using my new ProChrono Digital and it didn't miss a shot...
The pellets are H&N target 21.14 gr..  The first string I filled to 3100 psi on the pump.
2900 on the gun and shot down to 1900 psi.
1.  789      21. 836
2.  788      22. 837
3.  806      23. 837
4.  796      24. 842
5.  805      25. 849
6.  809      26. 846
7.  800      27. 839
8.  814      28. 836
9.  809      29. 838
10. 820      30. 836
11. 819      31. 840
12. 822      32. 834
13. 822      33. 826
14. 819      34. 830
15. 823      35. 823
16. 823      36. 822
17. 824      37. 819
18. 826      38. 818
19. 835      39. 803
20. 833      40. 803

Looks like you are learning a lot about your rifle 


I would fill to the same pressure ( 3100 psi pump gauge ), then adjust the hammer spring ( 1/4" hex wrench ) CW 1/2 turn at a time ( see pic ), until the STARTING velocity is 819 fps. Being sure to refill back to 3100 psi every 2- shots, until the goal is reached. I would do this and not adjust anything else, for now.


Once the shot string is established, then test to see if this combination is accurate   

[wimpanzee]

No I shot all 40 shots on one fill from 2900 to 1900 psi.

I'm an idiot, i only saw the first column of 20...added to the second column, not a bad string at all!

[mb4859]

Tim that's what I was thinking.  I was just waiting for someone to confirm my thoughts.  I'm thinking a little more spring pressure would open the valve a little better on the first few shots.  But will it make the middle shots go higher also?

[mb4859]

Would tightening down on the valve screw bring down shots #25 and #26 or should I not worry about a couple high shots.

[Ribbonstone]

A very good option would be to leave it as it is.

[HillGSA]

Tim that's what I was thinking.  I was just waiting for someone to confirm my thoughts.  I'm thinking a little more spring pressure would open the valve a little better on the first few shots.  But will it make the middle shots go higher also?

Yes, you are correct. More spring pressure will open the valve more/longer and raise the velocity.


You could fill to 3100 psi ( use the gauge on the pump ) try 1- turn CW on the spring, then shoot about 8- shots across the crony and post the results.


61 fps difference between the high and the low is a bit much, unless you are shooting close in. How far away will your farthest shots be ? 25 yards ? 50 yards ? 75 yards ?

[mb4859]

Well when I'm squirrel hunting I'm sure 40 or 50 yards would be a long shot under ideal conditions but I love target shooting out to 75 yards or more.  These guns aren't that much fun stacking pellets in a ragged hole at 20 to 25 yards.  But I can narrow my shot string when I'm long distance shooting at the house.  I'm not sure if I've mentioned it but I'm pumping the gun with a hand pump so I would like it to be efficient.  Tim when I do this will this likely tighten the string or just raise the fps across the board?  Either way I'll try it tomorrow.  Oh yea thanks all of you for your help.  I have really enjoyed shooting this pellet gun. 

[HillGSA]

Well when I'm squirrel hunting I'm sure 40 or 50 yards would be a long shot under ideal conditions but I love target shooting out to 75 yards or more.  These guns aren't that much fun stacking pellets in a ragged hole at 20 to 25 yards.  But I can narrow my shot string when I'm long distance shooting at the house.  I'm not sure if I've mentioned it but I'm pumping the gun with a hand pump so I would like it to be efficient.  Tim when I do this will this likely tighten the string or just raise the fps across the board?  Either way I'll try it tomorrow.  Oh yea thanks all of you for your help.  I have really enjoyed shooting this pellet gun.

Well, looking at your avatar, I can see that you have the Gen 1 Marauder rifle, so unless you or someone else has changed out the transfer port, the one in the rifle should have an id of .125, which when combined with the 21.14 grain pellets, at the velocities posted is probably close to being maxed out, meaning the peak of the shot string should not get much if any higher. Also, the Gen 1 rifles have a less stiff valve spring in them, so the higher pressure end of the spectrum ( 3000-3100 psi ) will be your friend, meaning it will help to close the valve quicker, which should go along with a flatter shot string.

With your stated shooting goals, I believe a velocity difference between the high and the low fps of the entire shot string, should be no more than 40 fps - but that's just my
thoughts 



Anyway, tuning usually takes a bit of time and tweaking to arrive at an acceptable shot string that suits ones needs - but that's part of the fun

[wormbobskey]

Don't mean to hi-jack your post, but just got done running my gen 2-22 Mrod across the chrono and with 14.3 CPHP I'm getting on average 828 FPS. Getting 40 shots from 3000 fill on my pump gauge down to 2000 psi. What can I do to increase FPS? I'd be happy with 30 shots per fill if I could boost FPS and FPE using the same 14.3 gr pellets. Again mb4859, sorry for hi-jacking your post.

[mb4859]

Ok Tim, I cranked the spring down 1 turn after pumping up to 3100 and was shooting too high so I ccw 1/4 turn and was shooting 329 so that is where I left it.  Here is the 2nd string.

1.   829     21.  853
2.   832     22.  851
3.   833     23.  851
4.   835     24.  844
5.   835     25.  849
6.   833     26.  847
7.   840     27.  847
8.   843     28.  841
9.   844     29.  839
10.  846     30.  836
11.  848     31.  832
12.  848     32.  828
13.  850     33.  822
14.  852     34.  820
15.  856     35.  815
16.  854     36.  810
17.  853     37.  807
18.  859     38.  806
19.  851     39.  796
20.  858     40.  795

[mb4859]

On my 1st string I got 28 shots with a 30 spread.
On my 2nd string I got 32 shots with a 30 spread at 10 psi higher average.
This time I shot the dots for accuracy and it seemed I had slightly better grouping at 800 to 820 psi.  I shot the string at 30 yards which is where I have sighted for zero.  It looks like I had about a .5" high to .5" low so a 1" variance in elevation in the full range of psi.  The wind was 10-15 mph so I'm going to try it again before I make any changes.  I think next I want to try a 770 - 800 psi string and see how many shots I get with that setup.  I bought me a better shooting rest yesterday to shoot for accuracy.  I bought the Fieldpod from Academy.  I think I'm going to like it.  It's light weight and very portable and suits my shooting set up.  My wife's tired of me leaving boxes and chairs set up on the front porch for my target practice every day.  I'm going to make a mount for the front of it to mount the chrony to so maybe I won't shoot my chrony.  I'm waiting on my grease to come in I ordered and I'm going to take my gun down and give change O-rings and give it a good lube.  Sometimes it is really hard to cock.  It gets almost all the way back and it seems to lock up.  I want to do some polishing.  I would appreciate any advise on where to start.  And Worm all's good.  We're just all trying to learn.

[wimpanzee]

I smoothed out the bolt on my rifle and pistol with a little graphite powder. I had to remove the hammer to get it all around the tube, but it is much more smoother now, and I rarely get the end-of-pull stickiness that i used to.