Ak v3 nozzle change how easy is it to do?

[Randymanpipe]

I have fitted a shiny new combat union rotary v3 hop chamber with purple prommy in my RPK 

but have had significant fps drop with the original factory nozzle.
 

Like 50-60fps drop so I’m assuming I need to fit the combat union nozzle that comes supplied with the hop unit. 

(I didn’t want to have to open up the gearbox) 

I have limited gearbox experience, is this the sort of thing I can do relatively easily or should I take it to a tech? 
 

iv only really worked on m249 gearbox which is much simpler I believe. 
TIA 

RMP

 

[Skara]

V3 gearboxes are a pleasure to work with, swapping a nozzle is a relatively simple task.

Take pictures of everything you do so you can backtrack when reassembling (or when you don't know where X bit goes), also be aware that the combat union nozzle is *TIGHT* against the cylinder head, doesn't affect performance but might be annoying.

 

[Adolf Hamster]

As with any gearbox keep a good track of shims when taking it apart, then you wont need to re shim.

The hardest part of a v3 (especially one with a qd mainspring) is getting the trigger in, i advise taking care when popping the halves to ensure it stays in the bottom half, hopefully it should stay put and you wont have to mess with it.

Otherwise once its split changing the nozzle is no different to any other box. As @Skara says the cu nozzle should be a little tight on the cylinder head because of the sealing o ring, as long as it still moves ok under spring tension (a little grease around the cylinder head tube on installation helps) then it's a good thing as it'll boost the air seal and hence performance.

 

[Randymanpipe]

Thanks for the advice, 

had a go at getting the gear box out tonight but came to a screeching halt when I realised my v3 gb has an ebb system and  I couldn’t figure out how to disconnect. 
tried to gently prise it off but didn’t want to break it!

any ideas? 
 
 

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[Adolf Hamster]

That white peice slides forwards off the gearbox same way the sheet metal retainer does.

 

[Randymanpipe]

That white peice slides forwards off the gearbox same way the sheet metal retainer does.

Thanks for the help/advice,

I managed to get the gearbox apart last night and have a play around / change the nozzle .

Even with a screwdriver inserted to stop the main spring shooting out it wanted to push up where it enters the piston so disturbed the trigger assembly a bit
 

I was able to grease all the gears while I had it open and get a feel for how the gearbox works/fits. 
 

The gears interestingly  had this weird brown sticky residue on them? 
not lubricating at all!
 

having put it all back together and tested and the fps has gone from 290-320 which is good. 
The rof has gone up a bit too now it’s all lubricated. 
 

Couple of minor issues are I’m not sure I fitted the trigger spring correctly as it feels a bit looser than before and the selector shoots full auto on both semi and auto.

I don’t think I checked the selector tooth alignment on the rear of the gb when re assembling though so hopefully that’s an easy fix. 
 

it’s a cheapy JG so would like to replace a few bits in there moving forward but will probably wait until the gun craps out first. 
 

found a really great v3 disassembly video on  YouTube that was a massive help. 
 

would be happy to open up and tinker again for sure. 
 

one last thing regarding the hop, 

with the cu hop unit and purple prommy rubber/nub with maximum hop on it only just lifts a 0.25 

What mod could I do to get more adjustment in the window? 
 

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[Adolf Hamster]

The gears interestingly  had this weird brown sticky residue on them? 
not lubricating at all!

Ahh yes, the ol' jg earwax "grease"

Couple of minor issues are I’m not sure I fitted the trigger spring correctly as it feels a bit looser than before and the selector shoots full auto on both semi and auto.

Sounds like the selector teeth jumped a couple of positions on reassembly, the joys of getting a v3 box into a reciever. Best method is to lie it on its side so gravity hopefully holds it in place for you.

one last thing regarding the hop, 

with the cu hop unit and purple prommy rubber/nub with maximum hop on it only just lifts a 0.25 

What mod could I do to get more adjustment in the window? 

Whilst i realise it's a contraversial opinion, i'm really not a fan of the prommy purple, it's ok as "standard" rubbers go but not anything special imo.

If you're running a unit as good as the cu then i'd be strongly suggesting the maple leaf macaron+omega nub combo, that'll have no trouble lifting the heavies.

 

[Randymanpipe]

Ahh yes, the ol' jg earwax "grease"

Sounds like the selector teeth jumped a couple of positions on reassembly, the joys of getting a v3 box into a reciever. Best method is to lie it on its side so gravity hopefully holds it in place for you.

Whilst i realise it's a contraversial opinion, i'm really not a fan of the prommy purple, it's ok as "standard" rubbers go but not anything special imo.

If you're running a unit as good as the cu then i'd be strongly suggesting the maple leaf macaron+omega nub combo, that'll have no trouble lifting the heavies.

interesting. 
iv always run purple prommys in my mg builds, never had an issue with them before. 

I’ll order the maple leaf macron with omega nub and compare performance! 
 

many thanks for all the advice ?

 

[Adolf Hamster]

Yeah i've always ran the macaron+omega combo with the combat unions and they've had no issue with regular ammo or even the heavies, bearing in mind my concept of "normal" weights starts at 0.3g ?

 

[Randymanpipe]

“Sounds like the selector teeth jumped a couple of positions on reassembly, the joys of getting a v3 box into a reciever. Best method is to lie it on its side so gravity hopefully holds it in place for you.“

So you were correct about the selector teeth. 
 

I took the gearbox apart again today and noticed the selector teeth were 1 tooth out of line.

Sorting this fixed the full auto in both positions problems but raised another issue.

In semi auto the trigger would not spring back on its own, you had to push it. 
As I suspected I hadn’t re assembled the trigger mech correctly and needed to open the gearbox again ?

God damn that trigger mechanism & trigger spring are fiddly as fk to get right and stay in position whilst closing the gear box ?

I got there in the end but I was starting to get emotional ?

I was considering upgrading loads of the internal parts but now I think I’ll just leave it until something breaks! 

Pic of how I’d fitted the trigger spring wrong ? 

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[Adolf Hamster]

God damn that trigger mechanism & trigger spring are fiddly as fk to get right and stay in position whilst closing the gear box ?

I got there in the end but I was starting to get emotional ?

in my defence, i did warn you

you get used to it eventually, but it is annoying.

on my jg i drilled a tiny hold in one side of the trigger bar and fitted a screw to stop it jumping free, although that risks weakening the pin and it then snapping (which i've had happen)

on a box that isn't too worn they usually stay put once you've got them in properly.

 

[Randymanpipe]

You did indeed,

my heart sank when I opened it the first time and the middle bulged out ?

So I found this amazing v3 gearbox disassembly video on YT which was a massive help, and it pointed out that usually there is a tiny hole in the trigger mech and gb shell but the screw is almost always missing from factory. 
 

As I disconnected the jg ebb it just so happened I had x3 of these tiny screws spare. 
I had to trim it down in length a bit as it stuck through the other side but helped massively hold the plastic housing of the trigger unit it.

The main issue I had was the screwdriver only went about 20mm into the spring guide so the middle of the gun spring would try to burst out around the cylinder pushing everything else up.

after a couple of goes I found a way to hold it all down and get that poxy shell closed ?

Just waiting for the mapleleaf bits to arrive and then field test it in sept. 

If it’s a significant improvement over my bullgear/purple prommys I may update the fleet of mg’s I have with Combat union/mapleleaf hop/rubbers! 
 

 

[Randymanpipe]

Yeah i've always ran the macaron+omega combo with the combat unions and they've had no issue with regular ammo or even the heavies, bearing in mind my concept of "normal" weights starts at 0.3g ?

So the macaron and omega arrived today and I quickly dropped them in at lunch time.

there seems to be loads more adjustment in the hop now and the fps has gone up again too. 

Not sure if it’s because I did the barrel nut up a bit tighter on the CU or the rubber fits better than the prommy? 
 

anyway I can now look to hop .28 or .30s out and touch people.

hopefully the build will pass its first test coming up in a few weeks! 

 

[Adolf Hamster]

Fps creep could be improved sealing, the ml buckings tend to have slightly longer feedlips which are great if they dont cause misfeeding.

There's also the larger contact patch which on paper should be able to spin up with less pressure, although some folks have reported the opposite (i think thats just the silicone based ml buckings).

Tbh, i just view them as the same effect as an rhop but infinitely easier to install properly.

 

[Randymanpipe]

Fps creep could be improved sealing, the ml buckings tend to have slightly longer feedlips which are great if they dont cause misfeeding.

There's also the larger contact patch which on paper should be able to spin up with less pressure, although some folks have reported the opposite (i think thats just the silicone based ml buckings).

Tbh, i just view them as the same effect as an rhop but infinitely easier to install properly.

hey Hamster,

Have had all my gear out prepping for a game next weekend and gave the RPK a quick test fire in the garden. 
 

Something slightly strange is occurring wondered if you had any ideas?

when shooting the majority of the rounds go straight and on target but 1 every 20 or so I’d say seem to come out sideways!  like 90’ left out of the barrel?

 

I got a cleaning rod out and and cleaned the barrel (it was filthy) but it still does it.

Iv removed the flash hider and it’s not so bad but does still come out at a funny old angle now and again?

The omega nub looked nice and square seated when I fitted it in. 
it’s not a massive problem as the majority go on target just every now and then I get a flyer and may hit a friendly stood to my 10-11 o’clock at games! ?

any ideas? 
 

TIA 

Greg

 

[Tactical Pith Helmet]

RPK inner barrels are often a fair bit shorter than the outer.   The slightest misalignment can be amplified by the length.  

If removing the flash hider helped, I'd guess misalignment.   

 

[Adolf Hamster]

RPK inner barrels are often a fair bit shorter than the outer.   The slightest misalignment can be amplified by the length.  

If removing the flash hider helped, I'd guess misalignment.   

Sounds like a strong candidate.

Certainly dramatic fliers left/right are most typically the bb striking something on the way out.

Packing the inner to stop it wobbling in the outer might stop this (if the alignment is right might need packed a specific direction), and generally not a bad idea for accuracy anyway.

 

[Randymanpipe]

Thanks peeps,

So, when I took the outer barrel end off (outer 2 parts) there was the smallest amount of wiggle play with the inner barrel like 0.5mm all round.

I have wedged a tiny rubber O-ring in around the outside of the inner which now holds it rock solid. 

Will test again later and see if that has remedied, if not I'm guessing the next easiest fix would be to buy and fit an inner barrel that actually reaches the end of the outer barrel. Current is about 150mm short! 

 

[Randymanpipe]

Would this effect compression parts though? 
would I need new cylinder etc? 
sorry for all the questions! 

 

[Adolf Hamster]

Would this effect compression parts though? 
would I need new cylinder etc? 
sorry for all the questions! 

150mm potentially you might be wanting a bit more volume.

Test it with it stabilised first then worry about barrel changes