[ardrummer292]

Hey guys, new member here. I joined specifically to get in touch with @1tonne about transplanting a V2.5 gearbox into a JG/GE SR25. It seems I can't PM until I've made a post or two, so here I am.

Edited to add
Pasting my PM here so I don't lose it, since it seems I can't send it without hitting a minimum post count. Maybe someone can help answer my questions?

I'm doing some pre-DMR build research, scouring the depths of Google for any information I can before spending my hard-earned money. My search took me to your very intriguing post here:

CYMA Sr25 vs JG/ Golden Eagle SR25

I want to get one of the 7.62mm and then turn it into an Electric Sniper rifle that fires 3.33 joules. So far with a normal M4 I can only make it shoot 2.94joules but I would hope that with the extra length in the cylinder, that I can get that little bit extra out of it. Well you might be able...

www.airsoftsniperforum.com

From what I understand, your plan was to use a JG SR25 receiver (which uses the odd JG/GE "elongated V2" gearbox) and fit a Retro Arms V2.5 gearbox inside. Did you ever go through with this? How awful was the fitting process?

I'm not planning on building a DMR off the JG/GE SR25, considering the superior SR25 options out there. Airsoft HK417s are a different story. VFC's 417 has a terrible weak gearbox shell, and the only fix (the Retro Arms reinforced shell) has been discontinued. The TM NGRS 417 has too many moving parts for comfort, especially considering the added recoil feature will make maintenance a nightmare. That leaves the relatively unknown S&T HK417 as my only real option, which appears to use this JG/GE-spec SR25 gearbox. I doubt I can trust the gearbox shell to hold together for a 2+ joule build, which is why I'm investigating a reinforced V2.5 gearbox transplant.

I hope this message finds you well, and I look forward to any input you can provide!

Austin

Edited again to provide more details about myself per forum rules

Name: Austin

Callsign: don't have one

Experience:
Started playing airsoft in 2004, so 18 years now (sheesh)
Been to quite a few national events, both as a participant and as admin/support staff
Active duty military for 4 years + 4 reserve, did a fair bit of cool training while I was in

Collection: entirely UKSF-centric
L119A2 10.0" (based off VFC Avalon, SOPMOD variant)
Transitional "L119A1.5" CQB (based off Krytac CRB)
TF Black-era L119A1 CQB (based off Krytac SPR)
L119A1 SFW (based off Krytac SPR)
Diemaco C7 (based off G&P AR15 A2 with Krytac gearbox)
L110A2 Minimi (based off CA M249)
MP5A5 (based off the Avalon model)
TM P226 E2
Cyma Glock 17 (based off CM030 AEP)
Elite Force Glock 19 Gen 3 NBB
Hoping to add an L2A1 SACTARASS (based off an S&T HK417), which is what brings me here

Kit:
Again, entirely UKSF-centric. Direct action and reconnaissance equipment covering operations from 2000 to 2020.

Other hobbies:
Playing drums, surfing, spending too much money on my truck, and working embarrassing amounts of overtime to fund all of the above

Location: Virginia Beach, VA

 

[1tonne]

Hi Ardrummer

Yes I did end up putting a Retro Arms GB into a JG Reciever.
There is a bit of modding that need to be done but overall, it can work.
The main mod is inside the Retro Arms GB. Retro Arms in all of their wisdom stuffed up the front end of the GB. So where the tappet plate sits against. They made it thicker so that it would be stronger. The issue with making it thicker is that the tappet plate is then seated further back and this then means that the air nozzle will not fit in the hopup chamber. So you need to get a mini die grinder and grind the inside of it to the front end to be the original thickness. When doing this, take note of and grooves that the tappet plate fit into and try and copy it. This will take you about 2 hours to do.
Then once you have put it together, you may also need to file the inside of the mag well of the receiver at the front so it will feed properly.

So there is a bit of work to be done but it can work. My rifle is shooting 3.3 joules and the GB even though I have made it thinner, it is still holding up just fine.

 

[ardrummer292]

Hi Ardrummer

Yes I did end up putting a Retro Arms GB into a JG Reciever.
There is a bit of modding that need to be done but overall, it can work.
The main mod is inside the Retro Arms GB. Retro Arms in all of their wisdom stuffed up the front end of the GB. So where the tappet plate sits against. They made it thicker so that it would be stronger. The issue with making it thicker is that the tappet plate is then seated further back and this then means that the air nozzle will not fit in the hopup chamber. So you need to get a mini die grinder and grind the inside of it to the front end to be the original thickness. When doing this, take note of and grooves that the tappet plate fit into and try and copy it. This will take you about 2 hours to do.
Then once you have put it together, you may also need to file the inside of the mag well of the receiver at the front so it will feed properly.

So there is a bit of work to be done but it can work. My rifle is shooting 3.3 joules and the GB even though I have made it thinner, it is still holding up just fine.

This is gold, thank you! I do have a couple follow-on questions.

Overall, it sounds like the V2.5 gearbox is nearly a drop-in fit for E1/JG/GE SR25s. I’m surprised that’s all that goes into it. If the only non-Retro Arms specific consideration is a bit of filing in the magwell, that’s honestly incredible. I figured there would be some awful process involving selector switch locations, selector plates, motor angle, or something like that. Makes you wonder why they didn’t go with the V2.5 gearbox right out of the gate due to greater performance potential.

As for the RA V2.5 gearbox itself, do you know if the shell thickness issue was addressed in later production runs? Alternately, is there some other V2.5 gearbox with a quick change spring that doesn’t have this design flaw? As another option, would it be possible to use a slightly longer air nozzle and put a sleeve on the sector gear nub to bypass the need for potentially high-risk modifications?

 

[1tonne]

There is another quick change spring version but it still has the same issue at the front with the front wall being too thick. Also note that it is an easy thing to fix if you are careful and think it through. But time consuming as you have to be very careful. (But it is definitely doable.)
Sheed who is on here, purchased the quick change version and he had the exact same issues.
I did contact Retro Arms and told them about the issue but they did not respond and so I would say that they have not changed the design.

Using a longer air nozzle does not work because the air nozzle will not be pulled back as far since the tappet plate does not retract as far as the normal GB. It will only retract enough once you have altered the front of the GB

 

[1tonne]

Here is a replacement stock JG GB
18airsoft

 

[ardrummer292]

There is another quick change spring version but it still has the same issue at the front with the front wall being too thick. Also note that it is an easy thing to fix if you are careful and think it through. But time consuming as you have to be very careful. (But it is definitely doable.)
Sheed who is on here, purchased the quick change version and he had the exact same issues.
I did contact Retro Arms and told them about the issue but they did not respond and so I would say that they have not changed the design.

Using a longer air nozzle does not work because the air nozzle will not be pulled back as far since the tappet plate does not retract as far as the normal GB. It will only retract enough once you have altered the front of the GB

Copy all, thanks for another in-depth answer. Looks like I have some power tool shopping to do. Is there an illustrated guide out there that shows the process and end result of this modification?

In the meantime, I have some additional research to do. I’m entirely unfamiliar with V2.5 gearboxes and their components, so I need to identify and source everything needed for this conversion.

 

[1tonne]

Luckily, I often take picks.

 

[ardrummer292]

Luckily, I often take picks. View attachment 19947
View attachment 19946

Thank you! Do you have a recommended mini die grinder bit for this task, both type and size? I have a Dremel, which looks similar enough to my google results for "mini die grinder" to do the job.

Just out of curiosity, what would happen if this gearbox was run in the stock configuration without any modification? Poor airseal, inconsistent feeding, something else?

 

[1tonne]

Your dremil will be fine. Sorry, I cannot remember which bits I used.

If run in stock condition the air nozzle will not go far enough forward and so it would have a bad air seal. Then if you got a longer air nozzle, it still would not work. Since the tappet plate is already back further than normal, it will not retract enough to let a bb through. So unfortunately, the front needs to be dremiled.

 

[ardrummer292]

Your dremil will be fine. Sorry, I cannot remember which bits I used.

If run in stock condition the air nozzle will not go far enough forward and so it would have a bad air seal. Then if you got a longer air nozzle, it still would not work. Since the tappet plate is already back further than normal, it will not retract enough to let a bb through. So unfortunately, the front needs to be dremiled.

Understood. From my own experience, I know that excellent airseal is crucial when trying to minimize joule loss with heavier ammo. As such, this mod is squarely in the "need" category rather than the optional "want" list. I'll have to figure out a way to pull off this gearbox modification without hacking the crap out of the shell in the process.