Evolution 7: JG M4A1 Gas Blowback Rifle

On September 9, 2010, in Evolution, Featured, by Mike

What price for milsim-level realism? With the Jing Gong/Golden Eagle M4A1 GBBR, the price is very right, and very tempting.  The PinoyAirsoft/GoMilsim team couldn’t resist hopping on the Gas Blowback Rifle wagon.  Lucky they took some videocameras along for the ride!

Technical Notes:

Internals and Externals

Jing Gong/Golden Eagle has just about produced a direct clone of the Western Arms M4A1 GBBR system, give or take some tolerances here and there. The differences in the materials used and quality control does knock overall quality down a notch, but overall fit and finish still compare favorably to the original Western Arms unit and its clone contemporaries such as the AGM.

Deviations from the mold are on the whole for the better. The system is built to be run on green gas, so everything from recoil spring to hopup is geared for that, so much so that the JG GBBR can hardly cycle on 134A gas. The inner barrel installed is M4A1 length unlike on the WA, and the extra 4 inches or so of barrel length lend the JG more power out of the box, around 1.8J average versus the 1J of the WA, strictly tempered for Japan regulations. The quality of the barrel itself is nothing special and the fit of the hopup will not produce any surprising accuracy with 8cm groupings, so you are getting what you pay for in that regard.  The nozzle is made of brass so this part has not had any breakage typical of other M4 GBBRs. The bolt head is otherwise plastic while the carrier is itself metal.  JG chose to stick with the non-negative pressure design on this so inherits the harder blowback but less gas-saving characteristics as well. On the magazine, the screws and some details such as the pins and gas port rubber on the magazine are different, but on the whole the differences seem to have improved the strength of the unit.

The finish on the JG M4A1 plastic body won’t fool anyone up close.  The true-to-real proportions of all the components and the etched Colt trademarks are great, but ultimately the finish on the plastic is a dead giveaway.  Spraying over with a dash of camo paint could certainly help, but unless lightweight weapons are your priority, it’s only a matter of time before you’re craving a metal body upgrade. The plastic receivers themselves are strong enough to withstand most use, until you take a hammer to it and try to extract some pins, but to be fair these parts are plastic.

Inconsistencies come up in some small but frustrating ways.

Outside, the etching on the barrel is in the wrong place. The front collar and delta ring are different enough from AEG proportions to prevent drop-in replacement of the plastic M4A1 handguards with A&K RIS or RAS handguards. The plastic parts inside and out don’t have the same level of consistency from unit to unit; our own review unit had a stuck hopup, which on examination was caused by excess plastic on the hopup dial that wasn’t cut cleanly enough. Plastic also features on the bolt head. The metal parts are not all steel. Some alloy typical of clone airsoft guns was used for the external as well as important internal parts such as the trigger and hammer. The proportions of the bolt carrier assembly are said to be slightly smaller than on the other clone copies such as AGMs, so that an AGM bolt will not drop into the JG receiver.

All in all though it’s hard to be completely frustrated with everything wrong with it, as the overall fit of the parts plus the reliable magazine still produces a gun that runs well out of the box.

Reliability

The reliability of a GBBR system is determined not only by the quality of the gun, but also of the magazine.  So to start with, the JG M4 GBBR magazine is a solid unit on green gas.  We experienced no leaking with our unit and misfeeds were rare, only showing up when the magazine is near empty of gas. We only had one unit to test long term, as unfortunately the JG mags are difficult to come by locally.  In comparison to EbayBanned-sourced mags (2 out of 5 that we picked up worked, while the rest had leaks or outright broken-from-factory parts), the JG mag is just about perfect.

The gun’s long-term reliability is not so good if skirmished as-is.  At over 500 rounds, the bolt catch starts to malfunction so that the gun continues to shoot even when all BBs are emptied.  At over a few thousand rounds the auto fire mode starts malfunctioning as well, outright unable to cycle after the first stroke and dumping all gas out of the mag in the process.  By the time this long-term review was done, more than 4000 rounds through the gun, the bolt catch is no longer able to hold the bolt back even when manually pressed down. Examining the bolt catch after all of this action shows the failure point is on the soft plastic patch on the otherwise metal bolt catch, which will have worn down to nearly nothing after constant use. We believe the plastics aren’t totally up to task for regular use, but not only is this ultimately the price paid, but the combination of plastic hopup, bolt head and bolt catch is also a holdover from the original WA design that hasn’t quite worked well endurance wise.

As with many GBBs and not just with the JG M4A1 in particular, and  in contrast especially to an AEG, the GBBR systems in general take much more effort, regular care and inspection to prevent these sorts of failure.  A more deliberate preventive maintenance regimen besides the occasional spray of silicon oil and gun cleaner might have kept the review gun running longer, but we do not believe it would have run much longer on completely stock parts.

Owning and Playing

The price is a big factor in considering owning the JG M4A1 GBBR. At around $100 USD (5,000 PHP), it’s only twice the price of two M4 GBBR magazines from one of the bigger brands.  At the time it launched a year ago, JG had the most affordable M4 GBBR on the market, and it was worth getting for the magazine alone.  On to magazines, the JG works well with AGM and other clone mags, but surprisingly has trouble with one King Arms M4 GBBR mag that we tried.  Costs don’t get much lower than this in GBBR terms, until the inevitable breakdown of plastic parts used in the firing and recoil system of the gun itself.

Playing with the WA GBBR blowback system versus with an AEG is mostly about getting the recoil and having more realism in operating the gun.

One real performance benefit of the GBBR trigger mechanism is it gives the trigger pull a true lag-less mechanical response compared to an unoptimized AEG electrical trigger system. This should mean just slightly more immediate “effect on your target” and less time to target and “lead”, but it’s a welcome bit of improvement. Another side benefit, less money spent on BBs. We only slightly say that in jest.

Otherwise to run a GBBR is really to run with more handicaps:  power output goes down much more when running green gas in colder weather versus when running an AEG, ammunition is very limited not just because the gas magazines can carry only 50 rounds, but also because magazines are so expensive to purchase and maintain, and every mag you carry feels like a full magazine even empty.

Verdict

With all the minuses laid out with green gas powered systems, it’s hard to consider it a practical choice to run a JG M4A1 GBBR versus the AEG systems that were built exactly to address many of those minuses.  But ultimately going with any GBBR system is going to be an emotional choice overriding the obvious handicaps.  Once you have tried a Gas blowback gas-in-mag system such as the JG M4A1 GBBR, the milsim freak in you is going to crave the realism, the feel of the mechanical trigger, the recoil and the crack of the bolt as it fires, even the more complicated reload with the working bolt catch.  The JG M4A1 GBBR is a low-investment way to have a taste of playing with a more realistic airsoft rifle.  All in all good fun while it lasts!


Transcript:
Airsoft is a sport of movement and skill, sometimes it’s a military simulation where scenarios and equipment are replicated to detail.
For an AEG wielder there is one detail that is mostly missing … a piece to complete the picture … recoil.

Gas blowback systems have been around for pistols a long time but rifle style systems are starting to gain numbers. Tonight we examine JG’s entry with the M4A1 GBBR.

The package comes with the replica M4A1, one STANAG style 50 round magazine, a pistol-style BB loader with adapter for top loading, some token BBs and a rebranded Western Arms Magna GBBR manual.

FPS on green gas was between 419 and 440 adjusted for .2grams or about 1.8Joules. Unlike the earlier Western Arms design this unit uses a 363 millimeter inner barrel. Grouping at 15 yards is about 8 centimeters, decent for a field gun.

Takedown is very similar to the real steel version. Push down the rear receiver pin from the left side. Flip the gun and pull until the pin locks. The pin is held by an even smaller retaining pin to prevent loss. Break the gun open by pulling from the top. This exposes the trigger mechanism on the lower receiver. Sliding back the charging handle removes the bolt. The bolt is comprised of a metal body, plastic head and brass nozzle. Don’t worry, there’s no firing pin unlike the real thing.

The upper receiver is held by the front pin which can be pushed down for removal. This piece takes some effort. The stock tube houses the recoil buffer which connects to the bolt.
It’s very much like the real steel design. Press the retaining clamp on the lower receiver to release. Then pull out the buffer along with the recoil spring. The recoil buffer is a plastic part which can be replaced after market. This recoil spring feels softer than the PDW’s that we’re also reviewing, it might explain why kickback is softer on this unit. The sliding lever on the stock allows complete removal.
Pull on the delta ring to remove top and bottom hand guards. This area can be augmented with a RAS kit.

The triangle sight has two pins that can be undone like in an AEG. You need to remove this to get to the gas tube. An armorer’s wrench is needed to undo the delta collar and barrel nut.
To remove the carry handle, simply twist the two thumbscrews, this exposes rails where you can attach a scope.

To put it all back together, just follow these instructions in reverse maybe you’ll get so good at it you can field strip blindfolded.

So is this gun good? Is it milsim?
Well, the gun is made in China, so it’s not made to be perfect. You just need to know what to expect. The bolt catch wears down after a few hundred shots. Even faster when you use full auto.
After two months this unit would fail to lock the bolt when the magazine went empty. Automatic mode broke at about 9 months. Not that you’d want to use it in automatic a lot. At 50 rounds per magazine you’re better off using single fire anyway. Changing magazines gives it a milsim feel. And having multiple mags hanging on your chest helps simulate the weight, if you can find them.
Other magazine makes like King Arms don’t line up correctly. If you can find the JG mags, grab them. They’re there most reliable part of this gun.

There are compatibility issues aside from quality control when it comes to WA-clone magazines. After market parts have to be approached with caution. Though this is one of if not the cheapest GBBR you can find, you get what you pay for. Expect to lay down more cash as parts wear down.

For updates and additional notes please visit our website at pinoyairsoft.org

That’s it for this evolution. Until next time.

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3,980 Responses to Evolution 7: JG M4A1 Gas Blowback Rifle

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  24. J-az-2 says:

    The King Arms bolt didn’t do any good :P It fit into the gun, but it was unable to cycle any BBs. This is a lesson to me; never buy things without looking into them.

    I ended up just buying a $7 WA Steel bolt catch after the original JG one wore down (after around 400 shots), and, after learning how to remove the JG bolt catch, it’s been working just fine for now.