So You Want to Build a Browning .50 Machine Gun...
M2 vs. M3
With the price of Browning M2
parts rising, many are looking to the M3 variant of the Browning .50 machine
gun as an alternative. Available M3 parts are generally in better condition and
are much less expensive than M2 parts are today. There appears to be, however,
some confusion about the M3, its differences from the M2, and its suitability
for a heavy barrel, or semi-auto gun. I will do my best to address the subject
here. If I have missed anything that should be mentioned here, or if you
disagree with any points made, please feel free to email me. I already consider
this a collective work, and I would like to be as accurate and representative
as possible.
What
is the Browning M3 .50 Machine Gun?
The M3 is a version of the M2
that was designed to sustain a much higher rate of fire than any M2 variant. It
was originally only configured as an aircraft gun. The M3 is an improved M2.
Why improved? In order to both achieve and withstand the high rate of fire, a
number of weak areas were modified. These are:
Depressors
are relocated from the buffer housing to the side plates. Apparently,
those two depressor tabs, which are unsupported at one end, flap around too
much (and may even break or dislodge) at 1200rpm. The relocation of the
depressors results in a modification of these parts:
·
Left and right side plates – depressors added
·
Buffer housing – depressors removed
·
Barrel extension – channels for depressors cut through
and relocated
Back
plate is modified to withstand greater forces. The buffer
on the M3 back plate is much larger, its diameter being equal to the width of
the back plate. The sides of the back plate that slide onto the side plate also
have an outside shoulder that wraps around the side plate to prevent the side
plates from deforming and releasing the back plate. Small recess cuts on the M3
top plate, bottom plate and side plates accommodate these shoulders. Since the
M3 was only intended for use in mounts (fixed or flexible), no provision exists
for trigger or spade grips on the M3 back plate.
Bolt
is lightened to allow higher rate of fire. Many internals were modified with new
design of the bolt. Basic geometry and dimensions remain similar to the M2
bolt. The top plate bracket has also been modified, though it is very similar
in geometry to the M2 bracket.
Extractor
& extractor cam modified. Generally, modifications here appear to make the
parts more robust. The extractor has a larger curved tab that grabs more of the
round than the M2. The extractor cam is wider and is secured by four rivets vs.
two on the M2 cam. It also has a change in angle that is more severe than the
M2 cam.
Top
cover is modified to grab more of the round than the M2 top cover. In addition
to grabbing the round at the rear, the M3 cover also grabs at the neck in front
of the link. This appears to prevent some unwanted movement at 1200rpm. The
change results in a wider feedway & shuttle.
Otherwise, the M3 cover is dimensionally identical to the M2 top cover.
The M3 Receiver has identical
geometry to the M2 receiver. The trunion is identical
(in later models the provision for a front sight has been removed). The side
plates are identical, except for the riveted components and a slight recess on
the rear edge for the M3 back plate. All of the tapped holes and slots of the
M2 are present on the M3 side plate. The top and bottom plates are identical,
except for the slight recesses in the corners for the back plate.
‘But I want a Heavy Barrel Browning’
Though the M3 was never configured by the
military as a heavy barrel, that doesn’t mean it can’t be. I have been using
the term ‘M3HB’ to describe and M3 receiver dressed up identically to an M2HB.
Yes, the M3 will accept the parts specific to the M2HB: barrel, barrel support
& bushing, back plate (complete with trigger and spade grips), front &
rear sights, and even the retracting slide group.
‘Won’t an M3HB fire too fast?’
Though the
M3 bolt is lighter than the M2, the weight of the heavy barrel acts to slow
down a full-auto M3HB to a rate of fire similar to that of the M2HB. The manner in which the M3 bolt is lightened makes it
easy to add weight to it in order to slow down the rate of fire further. A
semi-auto M3HB would not be affected in any way, of course, since there is no
full-auto.
‘I’ve heard that M3’s are difficult to build as
semi-auto guns’
Slight differences in the M3
did create some issues for semi-builders, but these have been resolved. TNW has
been offering their M3-Basic semi for quite some time now, I believe they would
be willing to build your M3 kit (they require you use their side plate).
Recently, as solution has been solidified for D.I.Y. and third-party builders.
Karma Metal Products (KMP) is now offering an ATF-approved Browning M2
Semi-auto sear kit that works on the M3. The KMP setup does require a
modification to the top plate bracket, but I am now providing the modified
bracket with M3-semi kits. Except for the bracket modification, all of the mods are similar to the M2. The only additional work
involved is placing and riveting the depressor to the right hand side plate (2
locator holes & 2 rivet holes). KMP also offers a beautiful ATF-approved
80% semi-RHSP that will soon be available with the M3 depressor holes
pre-drilled. So, an M3-semi is really no more complicated to build than an
M2-semi today!
If your application requires
authenticity or historical accuracy then an M3-based gun may not be suitable
for you. That aside, consider the M3 alternative for your Browning .50 shooter,
whether aircraft or heavy barrel, full or semi-auto.
To see general M3 kits, visit
gryphos.com/m3kits
To see new M3 kits for
semi-builders, visit gryphos.com/m3semikits
Revision
1.0 8/20/2005
Gryphos,
LLC