Fix Broken M4/M16 receiver tabs for good.

[Killbucket]

Got an M4? Are your rear tabs broken? @#$%^!!!....
I'm going to rescue this receiver upper that I botched up. First, here's a CAD drawing, and a jpg for the CAD-deprived. Make sure you print it at 300dpi, and the pattern will be full-size. I made mine from .090" ABS sheet. Stock ones are .075" thick, but there is a bit of room for slightly thicker material.
http://www.air-sharp.com/M4 repair tabs.dwg

The gun I'm going to resurrect with this repair is brand-new. I bought it so I could send the upper to Ka-Bar, who was very understanding about his showing up broken in shipment. (It's boxed, goes out tomorrow morning) so I'm going to repair this other upper that I have and make a whole gun out of the donor.
The upper you see little bit of was an early experiment. I had applied epoxy directly to the upper, and carved it to shape. Unfortunately, it made the assembly so stiff the tab snapped off the first time I went to snap it on. The lower assembly here is waiting for a strip and repaint, so I wasn't worried about it, and could focus on the repair.
But I digress. Your gun is busticated, and you aren't the first with the ailment, or the last.
First off, look for a replacement SRC upper. (Jungletoy used to have them, but now they have a new shopcart, and their search no longer brings one up). I paid $19.00 for one there earlier this year, so I know they are out there. Digressing again, but the point is, replace is better than repair. But let's suppose you live under an overpass, and you gun is broken. I don't know how you'd be reading this under a bridge, but I've seen the homeless with laptops...
I cut the parts out, and as you can deduce from the sequence of photos, one got welded in. The new part is located using the stock rear take-down pin, and the gun clamped shut after gluing. The squeeze bottle changes everything when using these glues. The included brush (fuzzy ball type) is only good for laminating large surfaces, (or use as an improvised torch when you're fifteen, and it's 1977, and you aren't properly supervised!)
The most important thing here is complete drying time. Oatey HD Grey adhesive (really, they should send me a x-mas card this year) will dry overnight, and hold the new part securely in place. I won't be standing on it, but the gun will stay together now.



Now here we are TWO DAYS later (Always have many projects going at once, it's easier to leave stuff alone to dry properly!)

Ugly, but effective. It is just as solid as it was before. Note in the top pic, the fillet of grey glue between the new tab and the body. I put a second application of glue on yesterday morning. This was to make sure this area was filled in well. If you look close at a GOOD tab, you'll see the same fillet.
Bear in mind, this doesn't have to be pretty, just strong. You could hack the parts out with wire cutters!

[Goodl2ussian]

sweet guide! thank you

[Renegade)]

Very neat, but when I snapped off the last of my back pins, I just ground both clean and now I can extract my upper by simply removing the front pin and sliding it off, makes getting at the barrel for cleaning, unjamming(never happened) and hopeup maintenance alot, ALOT easier.. and the mech and charging handle hold it all firm with the front lock pin.

[Styrak]

It doesn't want to flip up all the time? I would think that's very unsecure?

[Renegade)]

Originally Posted by Styrak

It doesn't want to flip up all the time? I would think that's very unsecure?

nope, The way V2, M16's fit into the upper is they slide in, the mech doesnt come straight down over top of them, so its very secure.. For a regular M4 without what ive done, ud have to take the entire gun appart, remove the lower, THEN slide out the upper to get at everything.

There is no movement at all.