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M16A2 Parts Kit Build:

For a while Sarco had their USGI Colt M16A2 part kits on sale for $425, about the same time Nodak Spud had McKay lowers on sale for $75. $500 plus a little shipping for a mostly Colt M16A2 clone sounded too good to pass up.

What came in the kit is everything you need to complete a basic rifle, less the lower receiver. The barrel is new, US production, with the Front Sight Block already installed (so the hardest part of the build is already done for you).

While the kit shiped without the auto-sear, it does ship with other full auto fire control parts, including the trigger, disconnecter, selector and hammer. These should be addressed first, since using full-auto fire control components in an AR-15 build is generally considered a bad idea. These parts need modifying to what is known as SP1 specifications. First is the disconnector:

M16A2 Parts Kit Build

The red arrow in the picture above points to the 'tail' on a full auto disconnector. This tail is depressed when the selector is turned to the 'auto' position, preventing it from catching the hammer as the rifle cycles. The disconnector on the right has had the tail ground off, so now even if a full auto selector is rotated to the 'auto' position, it still won't touch the disconnector.

The picture below shows the newly modified disconnector, along with the hammer, selector and trigger that still need some work. The red arrows point to the work that needs to be done. The back of the trigger needs welding up (maybe the last 1/8" of the groove - basically enough that won't interfere with the modified disconnector moving, but will prevent a full auto disconnector with the tail from fitting). The selector itself has a small fin (that depresses the disconnector) that needs grinding off, and the hammer has a lug on the back that interacts with the auto sear (not shown, not included in the kit either), so that needs to go too.

M16A2 Parts Kit Build

The picture below shows a modified hammer on the left, with the lug ground off with an angle grinder. The hammer on the right is yet to be modified:

M16A2 Parts Kit Build

This next image shows the modification to the selector. The red arrow pointing to the selector on the left shows where the fin used to be before being attacked with an angle grinder. The selector on the right still has its fin intact:

M16A2 Parts Kit Build

Once these modifications are completed and installed in the lower, the selector will be able to rotate to the 'Auto' position, but the rifle will function in semi-auto mode only, exactly as it does on the 'Semi' position.

The final part is closing the gap at the back the trigger. The triggers are very heavy/gritty when installed, this is easily resolved by polishing the surface that slides against the hammer (shown below). 5 minutes polishing this surface makes a world of difference:

M16A2 Parts Kit Build

These fire control group modifications take about 15 minutes. If you are not 100% comfortable making these modifications, it's easy to dispose of these and cheap to purchase a new semi-auto fire control group.

Now we can complete building the lower. We won't detail all the steps here, because it is identical to building any other AR-15 lower, and that process is widely and well documented elsewhere.

M16A2 Parts Kit Build

Building the upper is a little more involved, and requires some specialized tools (including an AR-15 Armorers Wrench, Torque Wrench, Vice and Upper Receiver Action Block). Again the process is well documented on various other sites so we won't go into detail here.

Our first problem with the kit materialized when we tried to install the furniture. The stock was in rough shape, but with some elbow grease, cleaners, and a Dremmel it cleaned up ok. The Colt handguards were a different story. One of the handguards had a tab missing, and a second tab snapped off trying to install it:

M16A2 Parts Kit Build

Having the handguards slide around is less than optimal, so we binned them. Fortunately we had a brand new set of Armalite handguards from a different project laying around (Our M16A4 Clone). They fit perfectly and looked almost identical.

The second concern was with the bolt carrier. Someone had gone at the bolt carrier with a mill and ground it to something resembling SP1 specs (so it couldn't possibly work with a full auto sear). There was no finish on the milled area, so it was rusting. The bolt carrier at the bottom of the picture below is the one that came with the kit. We ended up replacing it with one bought from GunBroker, shown at the top of the picture with the bolt from the kit installed:

M16A2 Parts Kit Build

Buying the bolt carrier blew the $500 target budget, but we still ended up with a sub $600 rifle, made mostly of USGI Colt parts (all except lower, barrel and handguards). The final result:

M16A2 Parts Kit Build

Overall the parts were in pretty good condition, with the exception of the furniture and the mutilated bolt carrier. There were are few scratches and marks here and there, especially on the flash hider, but overall less than $600 and a couple of hours work for the above rifle is hard to complain about. If we'd have stuck with the rusty bolt carrier the price would have been on budget. It shoots great too, it's rapidly become one of our favorite, and most used rifles.

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