Repairing HWABS - MGC M4A1 Receiver Lug

I know that I'm not alone in suffering from the Upper Receiver Locating Lug of my MGC M4 snapping off.
Since posting a Wanted Ad for a spare receiver I've received numerous messages from members complaining of the same Break.
Elsewhere here in the Forums' pages there are questions about repairing HWABS. Until now, it's been an impossible task BUT, at last, here's a very neat and tidy solution to the M4A1 problem  

First off, here's the broken Lug:



Fortunately, the break itself is clean and contained within a relatively small area. I have seen some that are much worse with far more receiver damage.

I'd been in contact with a Youtube poster, Peter Simmens, about the High Performance cartridges he made for his MGC M4 . My receiver broke while testing his cartridges but it's clear that this break is an inherent fault with HWABS MGC M4s and other AR-15 based models, NOT due to the cartridge  

Cartridge Video:-


Peter told me that he had experienced the same breakage and managed to repair it with Epoxy Resin reinforced with a metal back plate and metal strap. 
He very kindly offered to repair mine and I'm very happy with the results  

The Epoxy Resin is UHU PLUS Endfest 300 (available in various sized packs on E-Bay)


The metal back plate with strap can be seen alongside and also here


The back plate is cut to fit the Receiver and makes use of a moulded hole that passes vertically through the Lug and Receiver as can be seen in the photos. A peg is fixed to the plate which is drilled and tapped to accept the metal strap retaining screw.



Thoroughly de-grease the Receiver, Lug and Metal back plate. Apply the Epoxy Resin as directed by the instructions and assemble. Wrap the metal strap tightly around the lug and fix in place wit the screw.
The Receiver was then put into a pre heated oven at 150 deg for 5 minutes to cure the Resin.
The idea of placing a plastic part lie this inside an Oven was nerve wracking I admit, but the repaired receiver was unaffected by the heat. Obviously great care is needed not to leave it in the oven for too long  

The finished repair:-





As can be seen in the last photo above, any resin that squeezes from the mating surfaces needs to be removed and the back plate must remain flush with the Receiver to it fouling the Bolt Carrier as it travels with the Receiver and Buffer Tube.

I assembled the M4 yesterday. The Upper and Lower Receivers fit together perfectly and the Bolt Carrier travels as it should. Next step will be to Test Fire the model ....

I will follow this post up asap with details of a new Buffer made by Peter. The Buffer has a Socket Head screw set in its' centre which locates into a bored hole machined into a replacement metal plug that fits in the rear of the Bolt Carrier. 


New Buffer (Left) Bolt Carrier (Right) - Note Socket Head Screw in Buffer
 






Replacement Bolt Carrier End Plug (Left) Original (Right)














This arrangement stabilizes both Bolt Carrier and Buffer keeping them perfectly aligned and centred together as they travel along the Receiver. This stabilizing effect should reduce stress on the Lug.
The only disadvantage to this is that the Receivers cannot be opened just by removing the Take Down Pin. The end cap has to be taken off the Buffer Tube, Recoil Spring pulled out followed by the Buffer.
Then the Take Down Pin can be removed and Receivers opened as normal. A small price to pay if it reduces stress on the Lug  

Interestingly, Tanio Koba's M4A1 Carbine has a very similar stabilizer. He has a nipple protruding from the rear of the Carrier 






which locates and centres into a female recess in the centre of the Buffer. 




The advantage with Tanio Koba's method is that Receivers are opened normally.


My very grateful thanks go to Peter Simmens, Thank You Very Much

This is good news Cerwyn

Wow! Good news indeed!

Do you have any contact information for Peter Simmens, other than his YouTube channel? I have a slight feeling that he is german, so a direct contact would be a bit easier, methinks

Has he mentioned whether be plans to offer a 'repair kit' with the metal parts? Might turn into a gold mine for him and a blessing for a lot of modelgun fans...