by vulrath » Tue Aug 16, 2011 10:18 am
Okay, in this thread I'll be chronicling my (mis)adventures as I build my M4 challenge kit. If you are thinking about buying this kit, be forewarned: this kit is EVIL to those like me who are plagued with sudden inexplicable bouts of loss of fine muscle control in the fingers. That said, it's not impossible - I believe there are only two parts that have eluded my ability to assemble - the hammer, which on mine the tolerances on the outer buffer parts are off and when assembled binds the hammer from turning freely, and the E-clip that holds the nozzle to the bolt carrier, which fell off into my shoe and disappeared (yeah, I couldn't believe it either).
Before you begin, I'd suggest working on a fold-out table placed on top of a bedsheet laid out over the ground to avoid losing parts when dropped. I didn't, and now I'm paying for it.
So far, I've needed pliers, roll pin punches (I got around that - I'll explain), files, allen wrenches, and a phillips head screwdriver. I found it useful to have a nylon paintbrush for use as a punch when I don't want to mar the finish on larger pieces, and a hobby knife.
I got around having to use the punches by using a pair of visegrips with the teeth wrapped in a couple of layers of electrical tape. Open the jaws wide enough to fit around both the part and pin when closed using the bolt at the bottom, then open, tighten the bolt 1/4-1/2 turn, close. Wash, rinse, repeat. I learned that method doing my real AR15 lower (amusingly, the tape on the wrench I used is the exact same stuff I used when I assembled that). This method is also detailed further on AR15.com (where I originally learned about this method).
The first thing I did after I unwrapped the body was to find something to pound out the takedown pins holding the upper and lower receivers together. I'm not sure if they were anodized poorly or what, but the finish on both the pins and the body pieces was such that they bound pretty furiously. After I managed to get them apart, I took some of my favorite RS grease - MILCOMM TW25B - and applied some sparingly to the length of the pins, and in the channel for the retaining detents (if you do this, make sure you spread the stuff out with your finger, and easy does it - its lubricating properties are amazing). Push the pins in and out a couple of times to distribute the grease and to make sure you got enough.
Assembling the lower is pretty close to an AR15, so I'm going to glaze over installing the trigger, except I'm going to stress that you DO NOT FORGET THE DISCONNECT SPRING (I'm not sure it is called that on the M4, but I know it as the RS part). You will fire full auto on semi, and only sporadically at that as the recoil will bounce that part up and down, causing it to catch randomly. You can find a plethora of videos detailing how to assemble the real steel, which is really bloody close to the WA.
I still haven't installed my hammer, as I've elected to buy a new one that should be arriving in a few days, so I'm going to skip that, but I will say that if you use the stock one, the correct order for assembly is outer bushing->inner bushing->retaining washer->inner bushing->outer bushing. I tried pressing the inner bushings in with a wood vise - it is a royal pain to disassemble once they're in. I also had serious problems with getting the retaining washer to move appropriately to allow the retaining pin to fit through it (turns out there is a small cavity on other hammer bushings intended to alleviate this problem - when I go home tonight I'm going to experiment with countersinking one of the inner bushings on mine).
I skipped ahead and went on to install the selector and the auto sear. I found it easiest to install the auto sear, then the body retainer (really, the whole thing was a fustercluck, because I had started with the selector installed already, and the body block already in; I had to partially disassemble the block to get everything in correctly). I used a hobby knife to tension the spring from the side the selector does not go in from, then passed the selector partially through. Because of my unique situation, I had to stop to reinstall the selector spring and detent, then I pushed the selector all the way in.
If you have everything installed, congratulations! Do a function check, then move on to installing the bolt. Evike provided an updated diagram of the improved bolt, so that's how the assemblies go in, but we'll get to that in a moment. Put the roll pin halfway into the small piece (part_-_) and hook the long spring around it. Finish pressing the pin in using your visegrips, then tie a piece of thread to the other end of the spring. Thread it through part _-_, then tension it so that you can pass the roll pin through the loop in the center of the part (this is how I did it; you may have a different method that works just as well). Put your o-rings on. Assemble your nozzle as per the updated diagram.
Oil up your o-rings, and assemble the bolt carrier as per the instructions. BE CAREFUL WITH THE E-CLIP. It fell into my shoe, and I have yet to find it hours later (as such I need to find a replacement).
This is as far as I've gotten. I'll update this post once I get home to get part numbers, and I'll reply with photos as they're all on my camera at home and with more information as I continue to build. Hope what I have helps.