JG metal upper receiver with rear tabs

[Jackarutu]

To identify the weapon that is the subject of what I wish to discuss here-in has a few different names. Some call it the M4 R.I.S and other called it the M4 S system (DPMS M4 Carbine S.I.R., DPMS M4 S-System, KWA KM4S-TACTICAL). These arrive in North America under many different distribution paths such as Cyber gun, Palco Sports, KWA . .etc.

I don’t know for 100% but I believe all of these weapons are manufactured by either JG in china or one of JG’s families of sub contractors. In other words no matter what the distribution source I believe that if not all then most of the parts used to assemble these weapons have a single source and all come from the same tooling.

Throughout the years 2005-2008 these weapons came with upper and lower receivers made of ABS. And as such just as with any other M4 using ABS uppers the rear tabs would on occasional break off during use and cause the upper receiver to need replacing. And replacement is available.

Then in 2009 these same weapons started showing up with cast metal upper receivers. However, instead of designing them to slide together using the single pin method as used in other M4 weapons, JG elected to continue to use the rear tabs to hold the upper in position to the lower with the rear pin.

Now as most of you know when closing up the top receiver of an ABS type when the tabs moves past the notch in the rear of the version 2 gearbox the ABS will stretch and recover as you press slightly on them so they realign with the inside of the lower receiver (because as the tabs slide past the gearbox they tend to stretch wide and would go to the outside of the lower receiver if not guided with a slight pressure to force them to go inside).

With these newer metal uppers there is no such thing as stretching them because one can just be looking at the metal tabs and they fall off. Many of these metal ones I have opened brand new from the seller already have at least one broken tab. I’m not sure if they break when installed at the factory assemble point or during shipment or when opened by a value added wholesaler.

The next thing I noticed about these metal uppers is when opening them after they start to swing open they become stuck just as the tabs start to clear the back of the gear box so I have learned that unlike working with the ABS receiver I take out the front pin also and lift and pull forward to open them.

I conferred with another of the gun docs here on Airsoft Canada but I think I didn’t make myself very clear to him because his response was to avoid levering on the tabs.

Anyone who is familiar with the M4/M16 receiver already knows that the width of the rear of the gear box is a tight fit to get it past the upper receiver and while I would not call it levering on the tabs it does require a certain amount of force to swing it free.

My experience with this problem is the result of having worked day after day on this type weapon. Working on the ABS type is no problem at all but in my opinion working with the metal uppers is a pain in the back side and a solution for how to handle broken tabs needs to arise from our community.

To the best of my knowledge at this time replacement upper metal receivers (unlike the ABS forerunners) are not available.

Anyway after this long explanation of the problem I know Airsoft Canada has many machinists that are very talented because we have all seen their work. So here’s the question. Can a fix be made so one can grind off the broken tabs and add some type of a boss to the rear of the receiver so it can be made to function as the single pin metal M4/M16 receivers do?

Perhaps a repair kit using that epoxy used in tool and die work to glue some bosses on the rear of the receiver.

Any suggestions?

[HKGhost]

There are several threads on how to fix/replace the tabs on ASC. Most I've seen are just to solvent weld on a new tab. After looking at all those, I find it not to to be a great fix but a temporary solution. I did how ever found another solution that look like a better fix and more solid. I will be doing it this way if my tabs ever break. Here's the link: http://www.airsoftforum.com/board/lo...p/t173259.html. Hope this will help anyone that need to fix a broken tab.

Tom

[Jackarutu]

HKGhost,

Nice fix for the ABS upper but I'm not sure it would translate very well as a repair for the metal upper. I guess it would depend on finding an adhesive that would bond pvc to a metal surface.

[HKGhost]

Use JB Weld. It should hold strong if you prep the area very well. Sand and roughen the area to be bonded and you should have a solid bond.

Originally Posted by Jackarutu

HKGhost,

Nice fix for the ABS upper but I'm not sure it would translate very well as a repair for the metal upper. I guess it would depend on finding an adhesive that would bond pvc to a metal surface.

[Con Murder]

This is by far the best sollution I have seen for the tab problem. I had to search this down after a simple barrel swap turned into the end of cheap chinese meatal tabs! And after hearing that JB weld lasted 50k holding his motor, well I'm putting the gorilla glue on the shelf and getting some JB weld for this.