 |  | | | |  | |  |  | Benjiman NP Trail XL 1500 - gas ram upgrade |  | |  |  | |
 Posted: Tue May 08, 2012 5:06 pm |
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| mikemon |
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| Joined: 08 May 2012 |
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Hi to all forum members,,,
I currently own two air rifles and am addicted to the air rifles sport...yes sir I am....
I am curious to know if anyone has tried to upgrade the NP in the Benji NP trail XL 1500 to a more forceful piston, like per say 90-100lbs rated gas piston? Also, does anyone know what is the current NP in this Benji rated in its full stoke pounds? 35,40, or 50lbs?
I believe that since it takes a 40lb cocking effort to cock the benji, then the NP is a 40lb gas piston - but I may be wrong. 
My purpose of wishing to upgrade the Benji XL piston is to push a heavier pellet mostly reserved for PCP's air guns, those having a 2500-3000 psi resivoir.
My theory is as follows: If the gas piston has a full stroke force of "40lbs" which = (let say) 1800psi in the chamber @ 0.03ms = pushing a 7.6gr pellet @ 1200fps. Then changing the gas piston to a 60,90 or 100lbs piston at the same full stroke of 0.03ms, would create a higher psi in the same chamber which allows shooting a heavier custom pellet (20gr .177) @ 1000-1200fps and achiving a longer max affective range for the weight of pellet. But I may be wrong again in my theory. 
Please, if there's any member who could share their insight, and have some info or answers to the above. I would be greatly thankful
I have already made some modification to my Benji NP Trail XL 1500 that has shown its benefits, ie...made additional slanted ports to the shroud's end cap, added 4 vent holes to rear of the shroud, resurfaced the barrel's crown, lapped the barrel's rifling, modified and polished snare and trigger, polished compression chamber, changed piston seal. After the mentioned mods the rifles shots are incredible shooting a 10.5gr Crosman premier pellet. |
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| Posted: Tue May 08, 2012 9:40 pm |
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| AirGunEric |
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I don't think your "40 lbs.' calculation works- the cocking force is based on leverage- so in fact the gas strut pressure is greater than 40lbs.
I will also throw out that as with any "spring" powered gun- the limiting factor is usually not the power source- i.e. the spring or gas strut- but the size of the tube (how much air can be moved). As the Trail NP XL lives little room for increasing the stroke length, and you can't make the tube bore any larger without serious work (i.e. custom tube)- you could try a more powerful strut (perhaps one you can vary the pressure in)- but I suspect you will end up with little gain in power but alot more recoil/firing cycle disruption. |
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| Posted: Tue May 08, 2012 11:54 pm |
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| Slavia |
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| Joined: 31 Mar 2008 |
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| Quote: |
| I don't think your "40 lbs.' calculation works- the cocking force is based on leverage- so in fact the gas strut pressure is greater than 40lbs. |
I calculated it once with my G1 (there are spring force calculators on the net). You type in wire size, length at rest, O.D., number of turns, etc. and the calculator gives you the force at various amounts of compression. If I remember right that spring exerts about 70 pounds of force uncocked (with preload), and about 250 pounds cocked. The cocking effort is much less due to leverage, just as Eric said. It's like the jack on a car - a 2,000 pound vehicle doesn't require 2,000 pounds of force on the jack handle.
| Quote: |
| I will also throw out that as with any "spring" powered gun- the limiting factor is usually not the power source- i.e. the spring or gas strut- but the size of the tube (how much air can be moved). As the Trail NP XL lives little room for increasing the stroke length, and you can't make the tube bore any larger without serious work (i.e. custom tube)- you could try a more powerful strut (perhaps one you can vary the pressure in)- but I suspect you will end up with little gain in power but alot more recoil/firing cycle disruption. |
The advantages of a gas strut are that it can be left cocked without taking a "set" like a steel coil, and it works linearly, unlike a coil spring that wants to twist. That eliminates buzz, twang, and torque. Other than that it is like any other spring. Increasing the spring force will give a small gain in power and risks a large increase in "roughness." |
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| Posted: Wed May 09, 2012 7:53 am |
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| mikemon |
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| Joined: 08 May 2012 |
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| AirGunEric wrote: |
| I don't think your "40 lbs.' calculation works- the cocking force is based on leverage- so in fact the gas strut pressure is greater than 40lbs. |
Thank you for your quick response...  My "40lbs" used was just an example to word my question and form my theory. I really dont know what's the Benji NP Trail XL piston force forward nor extended rest pounds. That is my question, does anyone know or know of a site where I may attain the info? I have searched the internet but have not found anything close....  Lol |
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