MAIN INDEX SALES INDEX GUNSMITHING TOOLS AND JIGS SHOTGUNS AND ACCESSORIES RIFLES, MAGS PARTS AND ACCESSORIES HANDGUNS, PARTS MAGS AND ACCESSORIES COMMO GEAR NIGHT VISION, LASERS AND BINOCULARS SCOPES, SIGHTS, AND WEAPON LIGHTS TACTICAL NYLON, FIELD GEAR BACKPACKS BUTTPACKS AND STRAPS MEDIC KITS KNIVES, POCKET TOOLS AND MEDIEVAL WEAPONS VESTS AND LOAD BEARING GEAR BODY ARMOR AND HELMETS
AR15 Type Receiver Modifications
This is a short page with instructions on a relatively benign modifications to the AR receiver that will benefit owners and gunsmiths. The first is a fairly simple alteration that is set up to prevent the loss of small parts that often come up missing when a stock is removed from the rifle. This modification is basically a retention system for the rear takedown pin detent and spring assembly. If you do not have this modification, the spring and detent can be lost when the stock is removed for maintenance or storage and transport in a small space. It is also common for gun dealers and small vendors to sell AR lowers with the internal parts installed, and performing this upgrade makes it easier to sell the lowers as mostly assembled with less risk of losing parts between the time the lower parts are installed and the time a stock is installed later on.
This picture
shows a standard factory AR type lower (these from RIA). The parts shown
below the receiver on the right are the ones that you can reduce the risk of
losing when the stock is removed. Thus leaving you only to worry
about the buffer retainer and spring. The receiver on the left shows
the small screw being used to the spring, and in turn the detent and takedown
pin, in place. If any of these parts get lost, the gun can be
rendered useless. That is a real problem considering there are
times a survivor may have to remove the stock for storage or
transport.
Most of the
tools you will need are shown here. Basically a tap in size ********, a
tap handle, a Dremel or similar tool with a cutting disk and a pair of pliers
with a wire cutter. You will also need your handy small screwdriver
and it would help to have some tap fluid and touch up gun blue. Have
one small fine thread screw on hand, it will not matter much whether it is a
slotted, phillips, or hex head screw since you will be cutting the head
off. The screw threads should match the tap.
Install the
takedown pin as usual, complete with the detent and detent
spring. The detent springs that come with the various part
sets are often different lengths and even slightly different wire diameter,
which will alter the number of coils. Either way, run the spring in
until it stops and see how much is sticking out the back. Normally
you would push it all in and it would be held in by the stock. In
this case, check the length that is sticking out the back and cut off about
1/8" more than that much with the wire cutters. This should
result in the spring being about 1/8" short of the opening when you
put it back in. Pull the spring and detent out and remove the
takedown pin.
Using a little
bit of tap fluid on the tap, feed it in until just before the tap handle starts
running up on the back of the pistol grip. Back it out slowly and
carefully. Note that the tap will try to "wander" a bit
when you first put it in, but it will straighten out as it goes
deeper.
Once you get
the tap back out, use a pipe cleaner to clean the metal flakes and chips out of
the hole. Give it a few shots of spray cleaner/lubricant to get any
other crap or gunk out of there.
You are finished with modification to the lower, now for modifying the bolt to become a plug for the detent spring hole. Just put the screw in and turn it to where you still have the head, plus a little under 1/4" of threads sticking out the back. It should have at least 1/8" of thread inside the lower, with just little bit of tension up against the detent spring.
Fire up the
dremel (or similar moto-tool) with a thin ceramic cutting disk
installed. Cut the head off the screw and flatten out the part that
remains. Then cut a single slot in the part that is still sticking
out. You will then be able to use a small screwdriver to turn the
new headless screw until it is flush with the back of the lower reciever.
This will put more tension on the spring and thus the detent and takedown
pin. It it seems that you are cinching the coils up too tight and
the pin will not budge, back the screw out, remove the spring, and cut a few
coils off of it. If the screw/plug is long enough, you may grind some
length off of it, but you need it to be around 1/4" long to make sure it
holds under pressure.
You can use a
little bit of touch up gun blue on the screw to make it look professional, then
run it all the way in flush with the back of the lower. You are now
done with this simple modification and have very little risk of losing these
parts again during storage or maintenance.
BACK to Gunsmithing the AR-15 type rifles.
Related links: