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To reach your fps output goal it shouldn’t take much for aeg. I just recommend hpa. Opinion based though. You could do a lot more to it, in terms of upgrades. I believe you can run m4 hop units in it, but only certain ones because there is less room inside. So you can’t run units that have high tops with the larger adjuster wheel configurations. However if your hopup unit is metal I would just leave it and get an upgraded bucking and nub. Maybe a tightbore inner barrel too
 

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Discussion Starter · #5 ·
To reach your fps output goal it shouldn’t take much for aeg. I just recommend hpa. Opinion based though. You could do a lot more to it, in terms of upgrades. I believe you can run m4 hop units in it, but only certain ones because there is less room inside. So you can’t run units that have high tops with the larger adjuster wheel configurations. However if your hopup unit is metal I would just leave it and get an upgraded bucking and nub. Maybe a tightbore inner barrel too
do i need specific parts for the for the gearbox sins is not v2?
 

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Hi and welcome @Defender
How many ft/sec is now? JG SR25's are ~400ft/sec. Did you range test shoot it with various bb weights? You might not need that few more ft/sec output. You might just need to improve rifle's shooting quality (what @Blind Sniper suggested, better bucking, inner barrel etc).

i don't know what parts i have to use to achieve 450fps
In short you need a slightly harder spring & this starts the "domino" effect by installing a harder spring as you increase the stress to internals parts...That means time and money.

Do you play in Attica fields?
 

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HPA engine, F2, N7, Kythera, Mancraft, Fusion Engine.....
Decent hop chamber, aluminum SHS/ZCI is nice
Lap the original barrel, or lap a cheap 6.01
R-hop and a G&G blue or green bucking, or a Maple Leaf 2021/G&G blue bucking
Shim things here and there
Add a foam suppressor like a Novritsch one, unless you feel like cutting some foam yourself
And shoot BBs .36g+
 

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Thank you all about your recommendations but i think i am going to keep it just because it was 130€ and its my first dmr
I had a Matrix SR25 that used the same design gearbox your JG has. I used it for about a year and a half as a 1.8J DMR, and I had a consistent 235 foot range with it, using .36g bb’s. Its not a bad gearbox but it has the same limitations as any other 15 or 16 tooth piston gearbox has. So it’s doable, but it wont have any mechanical advantages over any other full cylinder standard gearbox AEG for air

The JG/Golden Eagle/Echo1/Matrix SR25’s use an oddball gearbox. It has the external dimensions of a V2.5 but have internals of a standard V2. The difference is that the cylinder head on these models are very long (the gearboxes are occasionally called “extended cylinder V2’s).

i have heard of people working to adapt an A&K style V2.5 gearbox to replace the JG SR25 gearbox but I don't have any information, first hand.

Upgrading an extended cylinder V2 is basically the same as upgrading any other V2 as the cylinder head is pretty much the only non-V2 part (with possibly the exception of the tappet plate), so just treat it like a standard V2. Typical air seal work and a M135-M140 spring should get the gearbox shooting 450 fps with .20’s but also chrono with whatever the field, and or what weights you use. The good news is that the gearbox usually comes with its cylinder head that is double o-ring, so you wont have to hunt down an upgrade part for that.

I would also bring the inner barrel length to about 363mm or so for better cylinder to barrel volume ratio. Its going to have the same air volume issues as any 15 & 16 tooth piston AEG will have with heaver bb’s (vs a V2.5 with a 19 tooth piston). The 509mm outer barrel is a detriment for any long range AEG, I run a 407mm in my V2.5 CA M110 and I still want to bring that in some for better volume for heavy BB’s.

I would recommend at least a good flat hop bucking and nub setup, the hop up unit is standard M4 (presuming this is a metal upper and lower receiver model),a quality M4/M16 hop-up would work well with it.

Good luck on your project!
 

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@1tonne performed this modification, and I'm planning to do something similar myself (Retro Arms V2.5 into a S&T HK417).
is it work? I see JG sr25 now pretty common now.
S&T is nice, just not great external.
 

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I haven't received the S&T HK417 yet, so I'm not sure. I'm going to try to transplant a bunch of parts from a VFC HK417 over to boost the durability, but I don't know if that's possible either.
On youtube had clip reviewed it, basicly it's not compatible with vfc
 

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On youtube had clip reviewed it, basicly it's not compatible with vfc
Do you have a link to that video? I’m trying to swap a VFC upper receiver and buffer tube over, nothing else.

Edited to add
I want a metal upper for increased durability. I plan on retaining the S&T outer barrel to ensure that the hopup interface at the chamber end remains correct.
 

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Do you have a link to that video? I’m trying to swap a VFC upper receiver and buffer tube over, nothing else.

Edited to add
I want a metal upper for increased durability. I plan on retaining the S&T outer barrel to ensure that the hopup interface at the chamber end remains correct.
russia but you can turn on cc transalte
 
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Man, this is gonna be one hell of a project. That upper receiver and outer barrel flex has got to go.

I really wanted a HK417 with a proper V2.5 gearbox, and this was the only one that would accept the transplant, so off we go I guess. Wish me luck.
anything news bro :D ?
 
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