G&G GR25 upgrade advice

[Azman1978]

Afternoon all.

Right gun in question is a G&G gr25. Standard v2 gearbox with elongated hop unit and cylinder head nozzle. 

Done so far:

Mosfet fitted (nano) and fully rewired to deans connectors. 

Prommy 590mm 6.03.

New g&g green bucking.

M125 spring

Shs high torque motor.

Polished the cylinder

Rebuilt and fully shimmed the gearbox. 

All good but only getting 245fps on .2g bbs at the mo. Probably a miss match on the barrell length so looking for a bore up set with no luck due to the cylinder head design. Any advice? Or how would others do it? 

P.s  gun pulls the spring with ease and no noise from the gb. No air seems to leak up the mag bb port when firing. Cant think where else to go. Oo what grease do you guys use in the cylinder?

Thanks in advance. Really want this fixed as it was an awesome gun just needed a tad more range. Hoping to get to the 80m mark. 

 

[sp00n]

Quick test, (with gun fully unloaded) invert gun, put some tissue over the magwell, fire gun

if tissue moves I would have a look at the spacer/adjuster on outside at the rear of the gearbox

 

[Azman1978]

Tissue does not move.

 

[Hangtight]

If you have a shorter barrel to hand, try that. At the moment you have over 50% too much barrel for a full cylinder using 0.3g BBs.

 

[Azman1978]

Will revert back to the original and give that a go tomorrow. Post back shortly. Thanks

 

[Azman1978]

Barrel changed to original. 300 fps. Got to be an air leak somewhere. 

 

[Hangtight]

A silicon grease will be fine for the cylinder.

Try the paper test again but with a finger over the end of the barrel.

Are you doing your fps checks with the hop wound off?

After that check the cylinder/cylinder head/piston seal.

How long is the stock barrel? And have you checked your chrono against another? Been got by that one before!

 

[Azman1978]

Think i have nailed it to the piston seal. Did the paper test no movement. Stripped down to gb and taken apart. Cylinder head seal is fantastic. Finger over end and blowing in the other with no leak. Piston seems very loose. Putting finger over end if nozzlr when together yhe piston still fires so must be air going round piston head seal. Original barrell length 509mm. New fitter is 590mm

 

[Azman1978]

Chrono is good as getting 335 fps on my delta recon. 

 

[Hangtight]

Try a 363mm barrel with a full cylinder firing 0.32g BBs. You may find you actually need to come down to a 120 spring once you get the efficiency up by getting the cylinder/barrel ratio right.

 

[Sitting Duck]

A std v2 full barrel is really for a 455mm barrel

YES - I know the G&G SR25 is 509mm & think some others like a G3 long mofo

as well as a a few others come with 509mm barrels but it really is pushing it for volume

If pushing the volume ratio then even correcting AoE can screw you up

If OP has corrected AoE he might need to consider only "half correcting AoE"

(improving it slightly but still need as much volume on that stretched volume limit)

As for bore up kits I personally wouldn't really bother coz if you do the maths it don't boost it that much

The std cylinder is about 23.8mm inside and an inch or 25.4mm = a wall of about 0.8mm

Can't make the outside much wider or the box won't close & the walls not too thin either

So when you take all into consideration percentage wise it doesn't boost the volume much at all

The AoE throws or reduces the stroke more than a bore kit will replace imho

So you have to work with what you got which is likely to be:

101% perfect seals - G&G piston heads are not great - bordering crap imho

the o-ring nearly always is a bit crap, try some other o-rings to get compression as close to perfect

(sealing straight away etc... to attain compression straight away or as near as damn it)

All other seals you say you have checked etc....

As been mentioned it is your volume to barrel and not a great deal you can do about the volume

just keep stroke as much as possible - half correct AoE or certainly not full or over correct AoE

get the piston seal perfect & try a shorter barrel to match the full std cylinder - max 455mm

I know some G&G SR25's shoot well but imho they must be tweaked to perfection, zero leaks

tbb barrels still no more than 509 if not 455mm - or they converted to HPA

The volume & maths & crap are pushing it all way out of the usual tolerances

It is why other longer AEG's like other SR25's use the longer v2.5

or SVD or G&G/AA L85's etc... and use a longer piston cylinder gearbox for 509+ barrels

Think G&G created the SR25 just for looks without really thinking it through and decided to wing it with a v2 box

Long waffle - but get compression/seals beyond perfect coz you need all the help you can get

Only half correct AoE at the most as you are struggling

Try a shorter barrel than chuck money into a bore up kit which imho won't boost volume much in the end

 

[Azman1978]

Only bummer is cant change the cylinder head unless i manufacture one. Ordered a ss cylinder and new piston. Going to play with this a bit to get it right. Will probably gasket seal the cylinder head in place. If that does not work i may be looking for a 2.5 gb shell and swapping some internals over lol but at least i will have some bits for when the nuprol gb goes. Will keep posted when the stuff arrives and i have finished with the v2 gb.

Ah also ordered a double o ring piston head (shs) to give that a wurl for compression seals.  

 

[Azman1978]

Kk folks. Update. New cylinder, piston and piston head installed. Compression is excellent. No air leak including with air nozzle on ( already has o ring in the air nozzle). Put back together and did a few test fires. First 10 shots 345 fps (0.2g) average ( with the longer promy barrell). Thought i would change to the oe barrell to see if that made a difference. It did. Dropped the fps down to 287. Ok. Swapped back to the promy barrell and then was getting 245fps again..... what the hell is going on???? Any ideas. Possibly the hop unit not sealing well enough. Using green g&g bucking.  Help. Want to get to a game jn the next few weeks. 

 

[Lozart]

My initial reaction is that it's a problem with the way you're reassembling the barrel into the hop unit.

 

[Samurai]

Check if the nozzle is in the centre of the barrel. Fire the gun so the nozzle is halfway back, not blocking completely the BB's path. Remove the battery and mag, get a flashlight and shine it in the magwell, where the BBs go up. Look down the barrel and you'll see if the nozzle is centre or not.

 

[Azman1978]

Dont seem to be able to feel a seal when mating the hop to the gearbox.. starting to feel this one may be past me. Replaced all sealing parts acept the cylinder head as no replacement units available. This is doing my swede in. 

 

[Azman1978]

Samurai. Cant do what you have suggested. The gr25 has a hop unit that mates fully to the gb.

 

[Azman1978]

Sorry was in dim wit land for a moment there. Right. Just done the paper in the magwell test and no movement other than gun vibration. Did what samurai suggested and the nozzles looks fairly central ( looking down 509 barrell) 

 

[Hangtight]

What happens if you try the paper test with a finger over the end of the barrel?

 

[Azman1978]

Still fires. No movement of paper.