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GHK G5/M4

#1 User is offline   aotsukisho 

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Posted 02 October 2019 - 11:36 PM

Got a preowned GHK G5 as my first venture into GBBRs. A friend of ours got a GBBR FN SCAR-H a few weeks back - I did not care for GBBRs nor did I even like SCARs of either variety, but seeing it in person and hearing it shoot is pretty much the best way to convince someone else to buy a gas rifle. (Gas pistols don't count cause AEPs do not perform well.)

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Here's the G5 out of the box. Came with the 12" Carbine kit installed, along with a few mags and spare parts. There was an AR stock adapter included which was nice, since the G5 folding stock was broken.

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I was looking for a rifle to run with Magpul furniture for a long time, and I think this is the one. I replaced the MOE-K slim grip with a regular MOE one which was more comfortable, and traded the AFG for a RVG since I realized I like those better

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Here is the carbine as it is, ready to go.
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#2 User is offline   aotsukisho 

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Posted 04 October 2019 - 02:13 AM

Did some experimenting and found that the GHK G5 magazine internals can fit into the GHK STANAG magazine internals and vice versa.

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Here's the magazines how they arrived. These two in particular were reported leaky by the seller.

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Removing baseplates from both mags. The STANAG baseplate end needs to be lifted and slid off, while the polymer G5 mag needs a lot more effort to sliding it off. Be careful too as the BB spring and follower assembly will probably shoot out of it if the bottom plate comes off entirely.

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Removed 'guts' of magazine from their respective shells. The STANAG mag had a (missing) screw at the bottom to hold it in, the G5 mag has a pin hidden by the baseplate when it is installed.

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Completely disassembled. Note how the two gas chambers are near identical, save for the STANAG mag one having a part extend out below the gas route in order to capture the screw holding the BB follower assembly together.

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Holding the STANAG BB follower assembly up to the G5 mag gas chamber, it mates up properly with the curves and alignment braces even though it's missing that part that the screw goes through to secure it.

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They both fit back into the other's outer shell. The floating BB follower assembly plus G5 gas chamber assembly in the STANAG shell, and the STANAG gas chamber with its extra wing for the follower assembly in the G5 shell with its independent BB follower compartment.

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I don't know if that floating BB follower assembly will cause feed or spacing issues under more strenuous usage, but for testing purposes both mags cycled the gun and fed properly. The pin for the G5 mag did not quite line up with the hole in the STANAG gas chamber, however it was by such a slight margin I am assuming it was due to wear and tear on the mags over their lifetime. I believe the pin for the G5 mag was also bent in the original gas chamber so the hole might have deformed as well. The bolt catch worked properly, although sometimes it did catch open one BB too early but that may be due to the fact that the bolt catch lever is slightly bent downwards.

Either way, the G5 shot successfully on full auto with both of those swapped guts mags. Things are looking good to convert all my mags over to the newest GMAG standard from GHK.
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#3 User is offline   aotsukisho 

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Posted 18 March 2020 - 01:18 AM

Cleaned all eight of my GHK mags as some of them were sticking while feeding, symptomatic of having dirt and grime in the channel due to the oils present

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Cracked open the magazines, remove the bottom plate and unscrew the single retaining screw

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Unscrew the two-piece bb channel from the tank, and remove the feed spring and follower

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Some springs are shorter than others, and most of them are tinged brown and need cleaning. Kind of hard to see due to whitebalance in the photo

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After some whisking through hot soapy water: springs, followers, and channels are cleaned. I will definitely look into jewelry type sonic cleaning devices to save time in the future

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Reassembling the tanks and channels, slide them back in

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Screw and baseplate reattached, mags are good to go

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Mags are now refreshed. Some of the gas route packings seem to be worse for wear, but all of them cycle properly in my GHK M4 so they are fine for now.

Basic maintenance like this is quicker to do in batches, this whole process took around an hour and a half I think.
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#4 User is offline   aotsukisho 

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Posted 20 March 2020 - 04:46 PM

Another magazine repair job that I did recently. This one I got for super cheap as it was damaged, listing showed that it had cracked feed lips and a broken empty mag cutoff lever. When I tested it out of the package, it also would not hold gas as its main valve was leaking. Fortunately I had some parts on hand to maintain my 8 STANAG mags so I could do a complete rebuild on this one.

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First things first removed the main valve. No matter how hard I tightened it down it still leaked the same amount.

Also found out that a WEtech valve key fits better in GHK valves than a GHK valve key. lol

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Pulling out the main gas tank, visual inspection shows that the rear part of the empty mag cutoff snapped off. I wonder what happened to this magazine.

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Removed the broken part, here it is compared to a new one

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Completely disassembled the main valve. Since the metal parts rarely go bad, decided to try swapping out all the o-rings first. The grey one is located inside the plunger tube, and is by far the one in the best condition.

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Reassembled the valve with the help of my vice to hold the plunger down so I can get the E-clip back on.

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This is how the empty cutoff lever is supposed to look like. Will be removing it temporarily to work on the feed lips and gas route packing next.

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Top set is new, bottom set is the one removed from the mag. The replacement set is a v2 mag spec, so I have to dremel off those wings below the feed lips. The white stuff on the gas route packing comes off when you rub it so I don't think it's anything serious.

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Got the new components installed, now to reassemble the mag. I didn't bother cleaning the bb channel, follower, or spring; those components were working just fine.

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Magazine is good to go, shown next to the components replaced. Normally I'd reuse the gas route packing but this one looks to be in fairly rough shape as well.

Tested the mag on full auto in my M4 and it's able to dump its entire contents so this repair was successful. I forgot how long it takes to fill up a GHK mag that's been atmosphere vented, could hear propane moving for over ten seconds.

Parts used to rebuild:
GAS-VA-ORN (O-ring set) - $3
G5-GMAG-04 (AR mag feed lips/gas route packing) - $3
G5-GMAG-05 (empty cutoff lever) - $3
Total was around $10 to completely rebuild everything important on the magazine. The gas tank is indestructible, and the polymer mag shell is tough enough to handle anything.
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#5 User is offline   aotsukisho 

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Posted 16 April 2020 - 11:56 AM

Finishing up chronicling all the progress I've made to where the M4 is now. I have it set up currently as a civilan PDW style SBR with Strike Industries furniture.

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Checking what modifications need to be done with a cheap charging handle I got from our local gun shop. GHK on the left, real steel on the right. I had already started sanding before taking the photo, hence why the aluminum is bare

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Dremel was a lot faster, and this is by no means a cosmetic part so I just left it like that

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Installing the Strike Industries Viper PDW stock

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Installed properly

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Also got a G&P outer barrel for WA system AR-15s, as I did not need the full length of the GHK 14.5" Government profile one.

GHK uses a modified WA system so it makes sense that the outer barrel needed modification. See the key at the bottom of the barrel, the G&P one needs to be widened

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A couple minutes with a dremel and the slot has been widened

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GHK uses AEG-spec metric barrel nut thread, which is incompatible with real steel barrel nuts using the imperial 1-1/4x18tpi threading. I used a die to recut the threads slightly so the SI barrel nut can be used. WD-40 makes for great thread cutting oil, but don't forget to clean it off afterwards as it may eat your O-rings

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Also took the time to replace the star chamber, as the one in the gun was quite worn down and getting pretty ugly.

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Got the SI rail onto the gun, and the Krytac rail next to it for comparison

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Looks good in my opinion, I know reading comments online that SI is not everyone's cup of tea but I enjoy their aesthetics a lot. I'm not sure if I can replace the magazine catch with SI's, as GHK uses an AEG style mag catch.

Other parts on the list to be swapped out to SI parts is the Vortex SparcAR riser and charging handle. I know that there are licensed airsoft -14mm CCW SI flash hiders, but I can't find them anywhere so we shall see.

I might have to swap out the barrel to a better and shorter one, as this one is shooting quite hot and with a lot of variation. I did a chrono test on the mountain (70°F-ish, high elevation) and saw the FPS on a fresh mag go from 450fps down to 370 with 0.25g...I normally use 0.32g but I forgot to bring my speedloader that day. The suppressor hides the end of the 363mm barrel, but a shorter one will allow me to use a normal flash hider in the future.
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#6 User is offline   aotsukisho 

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Posted 08 May 2020 - 05:15 PM

Picked up two more mags in need of repair, previous owner claims misfeeding which is characteristic symptom of cracked feed lips.

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Here's the mags, they look ok from the outside

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However both of them have that hairline crack down the center

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Pull them out of the shells

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Applying pressure spreads the cracks to be more visible. Both of these were already cracked all the way through so they will need to be replaced

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These mags were also GHK v1 so I needed to dremel the v2 feed lip wings off before installing them

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Sitting properly after the 10 minute job

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Procedure successful, ready to test. I charged the mags with propane and one of them needed a slight tightening of the gas tank screw at the bottom, along with a main valve o-ring change. Other than that, these should be good to go.

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Finally up to ten GHK STANAG mags, so I can run the M4 and G5 simultaneously with a full 4+1 loadout.
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#7 User is offline   aotsukisho 

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Posted 13 May 2020 - 04:50 PM

Short time travel, this was the process I went through in order to rebuild a lower receiver so I could have an all-black G5.

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Quick photo of the G5 slightly customized after I received it before I started major modifications

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If you replace the pistol grip with one that has a backstrap, you need to sand off the upper end of the tail

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Now it fits flawlessly

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Previous owner attempted to do the "epoxy mod"...unsuccessfully. This is just a bunch of silicone sealant, not rigid whatsoever. I guess it does have the benefit of absorbing shock though

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New lower receiver from Samoon ready to begin modification

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So nowhere I looked hat valid photos for this 'epoxy mod' so I had to piece it together from description. From what I can tell, you need to fill down the L shape from the rear of the receiver down near where the trigger group goes in order to reinforce it against cracking after repeated hits of the bolt.

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Filled in using JB Weld. Need to smooth off those surfaces as they interface with the upper receiver and rear of the bolt assembly.

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Starting construction of the trigger group. Unfortunately, no drop-in triggers here

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First goes the trigger itself

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Auto-sear sticking up

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Brass sleeve for the mag release. Very good

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Using a clamp to hold the valve knocker/firing pin in place while attached to its spring, as recommended by Samoon

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Also says to use a pipe of some sort to hold a spring...

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Thankfully that's over with. Hammer installed

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Function checked and ready to go

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Completed lower receiver ready to be swapped out

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Disassembly. I had also gotten another upper in tan/FDE so I could have two G5s

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Building/swapping the front units, with charging handle and front sight assemblies being swapped due to being tan. Also, the chamber has a proprietary interface with the outer barrel.

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Now there are two G5s, black rifle and tan PDW.

I ended up selling the tan G5 with all of the polymer GMAGs I have, so now I only have the black rifle configuration (and M4) with STANAGs. That is the one all further updates will be for.
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