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M16A1 Parts Kit Build:

Update 11/11/13: We get several calls/emails per week about this rifle or people looking for these parts kits. Unfortunately, other than the occassional parts kit on GunBroker, these kits have been sold out for a couple of years now, and the current owner of this rifle has no interest in parting with it.

The M16A1 with triangular handguards is an iconic rifle, so when we came across a deal on Sarco for a USGI Colt M16A1 kit (with new barrel), out came the credit card. The kit came with everything to build the rifle, except the lower. For a retro grey A1 style lower, there is only one game in town - Nodak Spud. Out comes the credit card again...

The parts in the kit were in mostly excellent to like new condition, far better than the M16A2 kit we built. The kit does come with some full auto fire control group components, which you don't want to use in a semi-auto build. The trigger, selector and hammer from the kit all need modifying. The disconnector had already been modified, and unlike our M16A2 kit, the bolt carrier was left unmolested.

The first step is to modify the hammer, trigger and selector to semi-auto/SP1 specs (we've outlined what needs doing in our M16A2 Parts Kit Build). Once that is done, it's time to assemble the lower, just as you would any other AR-15 (Picture below was taken before the parts were modified):

M16A1 Parts Kit Build

Detailed instructions for assembling an AR-15 lower can be found in numerous places, so we won't detail them here. The picture below shows the assembled lower (you can see the hammer has been modified before installing):

M16A1 Parts Kit Build

Now comes the hard part. The parts kit came with a virgin barrel, so we have to mount the Front Sight Block (FSB) and Parkerize the barrel, tasks which require more equipment than most people will have access to:

M16A1 Parts Kit Build

The FSB has been used previously so already has holes drilled. It is far simpler to install a new, undrilled FSB into a virgin barrel: lining up pre-drilled holes in the FSB and drilling the barrel to match exactly is not simple. There are several methods that can be used, including using screws, however we are going to attempt to install the FSB using the taper pins that came with the kit. To do this we will need a mill, #31 drill bit, 1/8" end mill, a 2/0 taper reamer, plenty of cutting oil, and even more patience.

Of course, spending a couple of hours knocking together a jig first doesn't do any harm either, especially if you want the FSB straight:

M16A1 Parts Kit Build

The jig helps align the FSB, it helps prevent the FSB slipping while drilling, and it gives you a flat surface to level against your table.

We start with an 1/8" end mill - if you start with a drill bit, the curve of the barrel will push the bit into the bottom of the FSB.

M16A1 Parts Kit Build

Then switch to a #31 drill bit and drill all the way through. Go slow, use plenty of cutting fluid, and the result should be nice and straight.

M16A1 Parts Kit Build

Then move to a 2/0 Taper Reamer. We start in the mill on a very low speed with plenty of cutting oil, and finish by hand. You want the taper pins to stick out by about 2/10th's of an inch before hammering - don't go too deep.

M16A1 Parts Kit Build

Now the slots are cut in the barrel, it's time to Parkerize it. First we degrease with Acetone, then onto the blasting cabinet to thoroughly etch the surface. Plug all holes, you don't want to etch the bore. We used silicon plugs in the barrel/chamber, and a toothpick with some tape in the gas port.

M16A1 Parts Kit Build

Let it bubble in the Park Tank at 190°F for about 10 minutes:

M16A1 Parts Kit Build

Complete the Park process, and it is time to put it all back to together. You can see in the picture below, we were pretty much spot on coming out the other side of the FSB with the drill bit and reamer (the dark parts are shadows from the flash, there are no discernible gaps).

M16A1 Parts Kit Build

Continue reassembly as you would any AR upper. Use a proper block to support the upper receiver, and torque on the barrel nut. I like to start with the torque wrench set to 30 ft/lbs, tighten until it clicks. Then set the wrench to 80 ft/lbs, and slowly tighten until the holes line up - if all goes well the holes line up before it clicks at 80 ft/lbs. Install gas tube and flash hider. For some reason this kit didn't come with either a crush washer or a peel washer, but instead it had a split washer, so lining up the flash hider how you want it isn't an option. This is a cheap fix later if you absolutely must have the flash hider lined up a certain way.

M16A1 Parts Kit Build

Put on the hand guards, add a sling, and you are done:

M16A1 Parts Kit Build

There is very little wear on this kit - a few rub marks on the furniture and upper, but the bolt is like new. For a $500 parts kit, plus $150 lower and $10 sling, you get a very iconic looking rifle made with mostly Colt parts, which is pretty tough to beat.


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