Marauder 25 tuning help

The Benjamin Marauder air rifle can be tuned. You can adjust the trigger and the rifles velocities for different fill pressures.

Marauder 25 tuning help

Postby mann » Tue May 16, 2017 2:24 pm

First mrod tune with new mds hammer 17 lbs spring . Ports enlarged to .154 about lighter valve spring and opened the front of the valve .040 shortened the 17 lb spring about 1/2 inch using 25.39 pellets tried the spring full length and tried to get to 900 fps plus I could get to about 880 but first shot was the highest and the rest were decending with the shorter spring and the hammer spring screw all the way out of threads as far as it would go found at a fill pressure of 2500 I got 818 to 832 back to 820 for 16 shots using 500 psi with the VMS screw all the way open I still have another 17 lb spring that isnt shortened yet at this tune at 3000 psi I get valve lock I think first shot is 788 to 831 on shot 24 which is the highest velocity any suggestions would be great thanks
mann
 
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Re: Marauder 25 tuning help

Postby mann » Tue May 16, 2017 3:38 pm

I forgot that I want to shoot the jsb heavies mk2 and just tried the 25.39 thinking if I could get them up to about 950 with a good string I would be able to shoot the heavies at 850 maybe but couldn't get them up that high with a decent tune I tried using the original hammer with the longer spring 17 lb and still just got a decending tune probably adjusting wrong vms wide open hammer spring for fps and ht for flattening​ out the string. This didn't work I tried with the mds hammer and it was the same thing . What I'm getting at will the heavies mk2 change the duration of the valve opening thanks again for any help
mann
 
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Re: Marauder 25 tuning help

Postby 22synrodn » Tue May 16, 2017 8:37 pm

Make sure the VMS did not get turned back in when reinstalling the set screw which is common and easy to do.

Fill to 2600psi and set your max FPS using the hammer spring. Leave the HT at zero and keep refilling the gun after a few shots to stay at 2600psi until you have your peak velocity set. Once set, fill to 3000psi and shoot a string. The higher pressure at the beginning of the string will cause the velocity to start lower than the peak set then rise to the peak and then fall back down to the starting velocity to complete the string. If not, I would be using my fill gauge instead of the gun gauge.
22 Synrod Unregulated. Tuned w/JSB 18.13gr:
31 Shots @ 30.43 FPE, ES 1.60%, 3000 - 2025psi


25 Synrod Regulated. Tuned w/JSB 33.95gr:
29 Shots @ 49.59 FPE, ES 1.96%, 3150 - 1840psi
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22synrodn
 
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Re: Marauder 25 tuning help

Postby mann » Wed May 17, 2017 3:05 pm

I tried what you suggested and must be doing something wrong I had the mds hammer in place regular length 17 lb spring got to 900 with a 2800 fill I think that is where I went wrong pulled the valve out installed the original spring reinstalled the valve took out the mds hammer installed the original hammer so I have original valve spring in place and original hammer with 17 lb spring and ports opened to .154 with this I started tuning at 2600 got 893 with 4 hs 1 ht vms at 3 tried a 2900 fill and it is still decending shot curve fist being the fastest I'm going to try again tomorrow at 3000 have to get my tank refilled don't know what to adjust to change the shot curve do I add more to the hammer throw is that what would lower the fill pressure I have a feeling that if I fill to 3200 that will slow the first shot down any help would be great
mann
 
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Re: Marauder 25 tuning help

Postby 22synrodn » Wed May 17, 2017 8:09 pm

Makes no sense closing the VMS when you are trying for 900 fps which by the way is too fast IMO. You can try and center the peak more towards 2700 psi for the higher velocity goals to get a bell curve on a 3000 psi fill. I would use the factory weight hammer and 17 lb spring to reduce cocking effort. It takes practice and trial and error to get it ideal and adhering to the psi fill closely when setting the peak of the bell curve.
22 Synrod Unregulated. Tuned w/JSB 18.13gr:
31 Shots @ 30.43 FPE, ES 1.60%, 3000 - 2025psi


25 Synrod Regulated. Tuned w/JSB 33.95gr:
29 Shots @ 49.59 FPE, ES 1.96%, 3150 - 1840psi
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22synrodn
 
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Re: Marauder 25 tuning help

Postby mann » Wed May 17, 2017 8:29 pm

I put the factory hammer back in and backed off the tension on the spring adjusted the ht and was able to get a shot string starting at 817 went to 834 end at 818 2800 psi fill ended at 2100 psi I will play with it some more to see if I can improve on it some yet for 16 shots . I think my Chrono was wrong before because I had bstaley tune in it and according to my Chrono it was running at 930 for 16 shots with a spread of 20 and I can't get close to that with a heavy spring and ports opened up with the VMS wide open waiting on the heavies mk2 to get here I suppose I will have to start over with those but I least I'll have a tune for the lighter 25.39 which I have alot off any ideas on how to make it more efficient? Thanks for your help
mann
 
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Joined: Tue Feb 17, 2015 12:28 am

Re: Marauder 25 tuning help

Postby mann » Thu May 18, 2017 10:58 pm

I wanted to do more tuning but I ran out of air and my shoebox went down ordered the parts for it and decided to build a internal ssg like 22synrod did drilled out the hammer polished the bolt put a nylon washer on the front of the bolt slid on my polished hammer found a nylon spacer that fits inside the hammer tightly to keep it straight installed cut down 17 lb spring installed it in the gun now waiting for pellets and shoebox parts I hope the ssg works well for the 25 it was easy enough to do I think for the gap adjuster I will use a longer bolt and a nut to lock the bolt in place what are people's​ thoughts on the ssg in the 25
mann
 
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Re: Marauder 25 tuning help

Postby 22synrodn » Mon May 22, 2017 5:17 am

The DIY SSG will work great in a .25 cal. That is a great idea going with a longer gap adjuster and putting a nut on it to lock it down.
22 Synrod Unregulated. Tuned w/JSB 18.13gr:
31 Shots @ 30.43 FPE, ES 1.60%, 3000 - 2025psi


25 Synrod Regulated. Tuned w/JSB 33.95gr:
29 Shots @ 49.59 FPE, ES 1.96%, 3150 - 1840psi
User avatar
22synrodn
 
Posts: 985
Joined: Sat Jan 10, 2015 4:33 pm


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