Reworking Guarder metal armalite bodies: solution to fitment issues

[MadMax]

I brought in a number of Guarder manufactured armalite receivers. I had heard that there were fitment issues.

They put toghether a pretty nice looking, well photographed assembly procedure, but they don't elaborate on step 19 very well:

http://www.intrudershop.com/show_pro...?idproduct=767
http://www.intrudershop.com/mmc/images/AR-32(B)/AR-32(B)A4.jpg

In a typical move of indifference, Guarder launched receivers which don't go together very easily. They don't allow enough space for the hop up module and the mechbox in the upper rec'r so there's a ridiculous amount of interference with the rear of the mechbox and the top of the lower receiver. It appears that in Guarder's mind, a judicious blow with a plastic mallet is an acceptable way to bash their receivers together.

I can't expect my customers to bash their receivers together. Disassembly would have to apply similar violence in reverse so the Guarder solution is not a good one.

Instead, I have worked out a simple rework to receivers which I'll be doing to my inventory to save my customers tunking headaches. If you have your own unreworked Guarder receiver, read on. This post might help you. While I do most of my mods with a milling machine, similar modification can be acheived with a round file or simple hand tools.


The problem:

When assembling the upper and lower receiver together, the user first slides in the hop up followed by the mechbox into the upper rec'r. The hop up is then rested against the lower rec'r but not fully pushed into the mag well. Only the lower stub sits in the rec'r at this point. This allows the hop up to be pushed forward to allow more space for the rear of the mechbox so it can clear the wraparound on the lower rec'r. Unfortunately the 1 peice hop up can't move forward far enough so the rear of the mechbox gets stuck against the wraparound on the lower rec'r.



The binding is pretty severe. I wouldn't be surprised if force (as guarder suggests) could damage the hop up or the lower rec'r.




Lower rec'r milled at the front:



I mill away a small area at the front of the mag well to provide a bit more clearance to the bottom tube of the 1 peice hop up. The extra bit of space lets the mechbox sit a touch forward in the upper rec'r.

EDIT:

I find cutting a notch straight through also works fine as the front lug on the upper receiver covers up a through cut notch between the lower receiver lugs just fine. It's easier to assemble once a through notch is cut as you can slide the down pipe on the hop up assembly right through the notch. I was being conservative with the shallow milling on the inside of the mag well when I first made this post. You can go straight through with a hacksaw pretty easily.


Heavy chamfer on rear wraparound:



I heavily chamfred the inside edge of the rear wraparound to give a little bit more clearance for the rear of the mechbox and reduce binding (chamfred edge is less jammy than a sharp corner).


Chamfred eyelets on upper rec'r:



I remove the sharp edge on the upper rec'r eyelets. The sharp edge has a habit of digging into bushings protruding out the sides of a mechbox. The chamfred edge can ride over bushings or at least provide a bit of undercut to help you slip a small screwdriver under the eyelet to lift them over a bushing. I also find that a razor blade works well for this.


File down corner on mechbox:



This is a mod that has to be done by the user as I don't have access to their mechbox. It's important to apply masking tape over the openings to your mechbox to keep filings out of your gears. It's not a hard thing to do and it'll protect your investment. It doesn't take long to file off enough metal to make for adequate clearance for your mechbox. I coloured the area which wasn't filed with a permanent marker to keep things clear. All you need to do is take down the upper rear corner a bit. Do not file down the raised patch at the back or you may affect the placement of the mechbox when you tighten the rear stock screw.



With the added clearances made in the receiver cutout, chamfer on the wraparound and the filing on the mechbox, you can get mechbox clearance without any forcing. This makes subsequent takedown possible and prevents damage to the hop up.

Luckily the rework is not too difficult. I can do them to my whole inventory before shipping them out. It shouldn't take more than a few minutes to file down the mechbox corner. None of the rework is visible to the outside once the rec'r is closed up.