The first time I assembled an AR-10 from parts and
subassemblies, I didn't have a lot of AR-10 specific documentation
and part and assembly descriptions didn't provide all of the
information required to make informed assembly decisions. When
closing up, the A2 extension tube went on, as did the buffer
retainer, buffer spring and buffer that were supplied as parts
within an A2 completion kit. The Magpul stock went on without a
hitch, the gun was looking pretty good, but it failed the mechanical
ops check. The bolt carrier would not lock open, nor would it travel
full open and pick up a round from the gun's magazine.
Never good signs.
A rookie mistake and it was then that I discovered an
AR-15 .223 Remington type buffer is approximately 5 7/8" (5.875")
long and weighs 5.2 ounces, while an AR-10 .308 Winchester type
buffer is 5 3/16" (5.188") long and weighs 5.4 ounces... and I was
not going to be able to put a 5.875" peg into a 5.188" hole. I had
AR-15 buffers in the shop, no standard AR-10 buffers could be found
in stock anywhere and, even if they were available, I didn't want days to shoot the new rifle. so
I decided to take a crack at making an AR-10 from the AR-15 part, or
at least end up with a heck of a paperweight.
The inner workings of a buffer, or... What the
heck is all this stuff?
The purpose of the buffer is to dampen the motion of
the bolt carrier and to compress the recoil spring and load it for
return. Knocking out the roll pin from the buffer liberates the
plastic tip, the anodized aluminum spacer, five tungsten weights and
the poly pads that separate each. The buffer itself is anodized
aluminum with a main tube O.D. of 0.686" with an I.D. of 0.569". The
weights and spacer have an O.D. of 0.547", The spacer has an I.D. of
0.310", the weights are solid, as are the between weight pads.
Why tungsten and not lead? Because men are no longer men and,
somehow, the idea of using lead and growing a third ear or letting a
few surplus brain cells wander off is enough to put them in a
tizzy... a 1937 Tizzy. A convertible I believe. Wasn't there a
window in this room?
After pulling the plastic end cap and emptying out
the contents, approximately 0.687" needs to be.. whacked from the
end of the tube. I say "approximately, because a little more won't
hurt, however, a little less could lead to cycling problems. This
buffer was chopped with a hacksaw, then face finished on a lathe.
What can I say, when you have a lathe, you have to use it, or people
ask why it's so clean... and then they'll snort, as though no one has
ever asked the question before. The buffer was reassembled after that
initial cut to show the resulting issues that need to be addressed after
buffer length reduction. As an
example, with the end cut off the buffer tube, the once recessed spacer can be seen peeking out
of the end.
The spacer needs to be trimmed back. Then there is the issue of the buffer
beginning life at five and two tenths ounces, two tenths shy of the
AR-10 part, then losing another tenth when it is trimmed to the
then losing another tenth when the spacer is proportionally trimmed
back. Ultimately, four tenth
ounces more weight must be packed into a smaller space.
Use whatever tools are available...
The first time I attempted this modification, I
chucked the spacer into the lathe, removed material and filled the
open space in the buffer tube with lead until I got to the correct
weight. As a bullet caster, I have lead at the shop
and some friends in local construction occasionally drop off old
lead flashing collected during demolition. At 0.050" thick, half
inch slugs were cut out with a shim punch, each adding one tenth
ounce of weight to the buffer assembly until the spacer was reduced
to one half inch and the sum of all parts equaled five and four
tenths ounces. The was lead dead soft so
wouldn't bounce around much in the assembly when the gun was fired
and it was quiet in operation.
The final step was to center and cross drill the end
of the buffer with a 0.120" drill to accommodate the plastic tip's
locating roll pin and to clean up any remaining burrs. The finished
length was 5.150" overall, weight was five and four tenths ounces
and it ops checked and fired without a problem.
This was, of course, actually the beginning of a
series of projects. The first unit took four hours, much of which
was head scratching. No, thinking, not psoriasis. The next took
forty five minutes at a reasonable pace, but with a little more
experience and knowledge. Several buffers have been constructed with
varying weights and spring combinations to suit certain types of
light and heavy handloads. Some with different fill substances have
done a better job of dampening harmonics and recoil.
In subsequent efforts, I've taken both buffer tube and spacer down
to correct dimensions with a belt sander, I've used .45 caliber
bullets in place of tungsten and lead slugs and I have poured molten
lead alloy directly into the tube for a tight fit in place of other
multi part weights. All part of what makes working on firearms
interesting and the source of ongoing education.