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PostPosted: Sat Jan 14, 2017 2:13 pm 
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Location: Likely outdoors, SW Ontario
Howdy,

Wondering if there is a mod to the Benji Legacy NP .22 innards that will gain me 40-70 fps? (akin to Benji Trail NP or Steel Eagle I imagine)

Mine shoots 427fps using RWS Superdome 14.5 grains.

For that matter, wondering if there is a member living in the Stratford Ontario (London/Kitchener) area comfortable cleaning, tuning, and doing such a mod?

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PostPosted: Sat Jan 14, 2017 4:57 pm 
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The gun is easily capable of breaking 500, even 700, so it's up to you how much power you want.
If you just want to get closer to the legal limit then I'd imagine a good tune should do the trick. If you want to get right on the edge of the limit I suppose it'll require a little mod since I assume as-is the guns are made to ensure they never break the limit as-is. I'm the type that would push the limit, so I'd tune it, then start altering it to increase power until it's perfect.
I would do that by shortening the piston, but you would have to plan it out a bit after knowing exactly what piston and spring you have now.


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PostPosted: Sat Jan 14, 2017 10:50 pm 
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Chevota wrote:
...I would do that by shortening the piston, but you would have to plan it out a bit after knowing exactly what piston and spring you have now.


Thanks for the reply, is shortening the piston a modification, or is it buying a shorter piston?

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PostPosted: Sun Jan 15, 2017 8:39 am 
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Location: Dryden,Ontario
I just "tuned" a Steel Eagle np2.My gun had a weaker spring and a hole drilled in piston.welded hole, sanded seal ,put full power spring in.Was hard to shoot.Put weaker spring back in and very smooth now and more power than oem.Just guessing but around 600fps maybe.Un scientific testing was out of box 50% penetration on 1" board @35'.full power spring and other mods,100% penetration @35".Current setup with other mods and weaker spring about 75% penetration.Hope this helps.I have a PAL so was not worried about going over the 495 fps threshold.


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PostPosted: Sun Jan 15, 2017 8:55 am 
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Plink-Panther wrote:
Chevota wrote:
...I would do that by shortening the piston, but you would have to plan it out a bit after knowing exactly what piston and spring you have now.


Thanks for the reply, is shortening the piston a modification, or is it buying a shorter piston?

It seems like Crosman/Benjamin used differrent methods to de-tune.The only way to be sure is to take it apart.I chose to weld up hole in piston but others have had good results with JB weld.How far does barrel go when cocking?Only 90 degrees or so prob have long piston.If barrel goes past 90 degrees and comes close to trigger guard prob has a hole in piston.I just went through this and there are so many variables that pulling apart is the only way to tell.


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PostPosted: Sun Jan 15, 2017 5:55 pm 
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Here's a pix of that cocking angle Sid mentioned, provided by another member.
The lower is a full power gun, the upper is a 500fps .22. A 500 in 177 would be ~90 degrees. These angles are estimates as the guns can vary, but gives you an idea on which piston you have. They also use holes and lighter springs as mentioned so you could have a combination of things.
Making a piston shorter can be done by buying one $$, or cutting yours. If you want to stay <500 then you'd have to cut yours because the bought one will be too much power. There are exceptions if other things are used, like a lighter spring, but with your gun you could dial it in by cutting the piston. You'd really need to open it up and find out what exactly it has, then I/we could form a plan. I could guesstimate but odds are it'll take a couple tries. Plus you'd have to be sure you're legal, so if you get 499fps with your pellets, will it be illegal because one JA made some light pellets and those exceed 500.... I'm not sure how the law works up there so that's on you.
But bottom line is you can dial the power to anything you want up to >3x the power you have now.
So with 14.5gr and 427fps you net 5.87ftlbs power. A 9.5gr will likely come out >530fps so if the law includes any commercially available pellet then you might already be illegal... Hopefully there is a weight or ftlb limit so you know where the line is. For example they allow to you to exceed 500 in 177 as long and xxftlbs in not exceeded, which solves the light pellet problem. In .22 I thought it was simply 500fps, but that's unfair with all the light pellets out now.


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PostPosted: Sun Jan 15, 2017 6:03 pm 
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Very Grateful to Sid & Chevota for the efforts of writing and sharing your experience. Much appreciated folks 8)

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PostPosted: Mon Jan 16, 2017 8:14 pm 
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My knowledge is very limited.I have only gotten into this airgun thing about a month ago.I pretty much learned everything here and e-mails to Chevota.So i can only comment on what I have done.If you have some mechanical ability they are pretty simple machines with tight tolerances.i never had one apart either but take your time and you should be ok.If in doubt take lots of pics before and during disassembly so you have something to go by.Exploded diagram and parts list at crosman.com if you want to see inside before you try.good luck.


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PostPosted: Mon Jan 16, 2017 8:19 pm 
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Thanks again Sid,

Actually just decided today that this rifle will be up for sale in a few weeks so I will let someone else tinker :wink:

Thanks for everyone's help ~

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PostPosted: Sat Feb 25, 2017 3:54 pm 
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Location: Sidney Bc, Canada
Hey.. sorry, this post is a little unrelated but is still also kind of related. I recently put a new spring in my optimus, the full strength spring, I figure it's still shooting under 1000fps due to the lack of crack. The cocking degree is around 90 degree, The piston was not ported in the top, I'm assuming it's probably the 170mm (longer piston) what is the length I would need to cut it down to? I think I heard 150mm was the full strength piston made for the optimus.. Anyone have any information?


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PostPosted: Wed Mar 01, 2017 7:48 pm 
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I thought I had given that you? Maybe someone else... Anyway, see the below pix which should answer your questions:
 


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PostPosted: Sat Mar 04, 2017 9:41 pm 
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I cut the 170mm piston on a new crosman Shockwave NP .22

Went from 430 fps to 580 fps. Not sure if the gas ram is the full power version. I've got an aftermarket gas ram coming in the mail, I'll likely try swapping it just to see.

It shoots very smoothly and accurately right now, I won't be disappointed if this is where I keep it.

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