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U.S. Army Marksmanship Training Unit Standards &
Procedures - Rebuild the .45 M1911A1 Pistol to USAMTU
Specifications -
1. Testing
The pistol will be set up and held in a recoiling type test cradle or
machine rest such as the Heg Rest, Ransom Rest or equivalent.
2. Ammo
Test ammunition shall be caliber .45 Match hardball (full metal jacket)
or
wadcutter as appropriate. Average extreme spread for three consecutive
groups of ten rounds each are not to exceed 2.5 inches with no group
larger than 3 inches for wadcutter pistols and 3 inches average for
hard
ball. No hardball group may exceed 3.5 inches.
3. Fitting the slide to the receiver
a. Select a slide which fits as closely
as possible on the
receiver, having a minimum of horizontal
or vertical movement
on the receiver.
b. Relieve the outer edges of the rails
on the receiver to remove
all phosphate finish from the bearing
surfaces.
c. The slide is now ready for initial
fitting to the receiver.
d. Place the slide (with the muzzle
end upright) into a smooth
jawed vise approximately 3 inches from
the muzzle end
(meaning the three inches of the slide
aft of the muzzle are
above the vise jaws). The top of the
slide should be extended
out from the left side of the vise so
that the vise is gripping near
the slide's rails.
e. Gently squeeze in steps of 1 inch
at a time, for the complete
length of the slide. Take extreme care
not to squeeze
excessively. The desired fit is a snug
fit and yet the slide
should be capable of being moved on
the receiver by hand.
Note that the slide may be squeezed
much harder at the rear of
the slide without crushing (because
this area is the beefed up
section of the slide!).
f. After the squeezing is completed,
apply lapping compound
(GK-7A or any 300-400 grit compound)
to the slide. Slip the
slide onto the receiver while the receiver
is correctly held and
supported in the vise. Work the slide
back and forth until the
slide moves freely without binding on
the receiver's rails. Wash
out the compound with solvent (or Gun
Scrubber, etc.), replace
the slide on the receiver and check
for movement by placing the
slide into the firing position. The
movement check is made by
grasping the muzzle end of the slide
in one hand and the
receiver in the other hand. Then move
each part in opposite
directions and check for any HORIZONTAL
movement.
g. If any horizontal movement is detected,
repeat steps 3a
through 3f as many times as necessary
until there is no
perceptible horizontal movement.
h. After all horizontal movement is
eliminated, the slide is then
ready for vertical fitting. With the
slide in the firing position (also
called the "battery" position), grasp
the muzzle end of the slide
and determine the amount of vertical
movement.
i. Remove the slide and insert a parallel
bar for swaging the
receiver rails. Normally a bar 0.1170
inches thick is a good one
to start with. A set of ten bars is
needed, graduating from
0.1100 inches thick to 0.1200 inches,
5 inches long and 3/4
inches wide.
j. Using a 4 ounce ball peen hammer,
swage the receiver's
rails. The recommended technique for
swaging is to hold the
bar snugly and straight against the
channel surface of the
receiver and then use a highly polished
hammer which has had
the edges of the head broken lightly.
Use an overlapping stroke
with the hammer face being held as nearly
parallel to the rail's
surface as possible. The rails must
be swaged as smoothly
and as evenly as possible.
k. When both rails are indicating an
even fit on the parallel bar,
again relieve the edges of the rails
to remove any high spots.
Use GK-7A for lapping the slide to the
receiver.
l. After lapping, recheck for VERTICAL
movement. If any vertical
movement still exists, repeat the swaging
with the next smaller
(thinner) parallel bar. Continue the
swaging process until no
perceptible vertical movement is noted.
m. Lap the slide and receiver until
the slide will move under its
own weight when the receiver is tilted
and also no loose play
(either horizontal or vertical) is noted.
n. Polish all work surfaces to remove
all hammer strike marks
or file marks or other blemishes.
o. Check the fit most carefully as this
fit is the foundation of the
entire operation. Repeat any of the
earlier steps if a perfect fit is
not achieved.
4. Fitting the barrel to the barrel bushing
a. Get an arbor that will hold
an oversized bushing and set up
the arbor between centers on a
lathe. Turn to achieve a good
fit. The nominal outside diameter
is 0.7020 inches. While
turning the bushing, be careful
not to deform the retaining lug.
b. Measure the barrel diameter
at the muzzle end. Install a
precision reamer in the lathe
and ream the inside of the
bushing to the exact size of the
muzzle end of the barrel. This
should be 0.5790 inches.
c. With a high speed hand grinder,
grind a slight radius in the
bushing to allow the barrel to
swivel slightly. This permits the
barrel to enter the locking lugs
of the slide without any binding.
Take extreme care when grinding
the inside radius so you do
not remove any metal from the
center of the bushing as this is
an important fit (actually, it
is the most important fit!) and must
be precision ground. The barrel
must slide back and forth in the
bushing without any horizontal
or vertical play.
d. The bushing should be a press
fit and should require the use
of a barrel bushing wrench to
install or remove it from the slide.
5. Fitting an oversized barrel to the slide.
a. Insert a new oversized barrel into
the slide and move it as far
to the rear of the slide as possible.
Observe the amount of steel
to be removed from the barrel's tang
in order to achieve the
desired fit of the barrel hood and lugs
into the battery position
(firing position) of the slide. A layout
die is recommended to fit
the tang squarely to the slide.
b. The tang must be cut in a manner
to maintain the original
90ø angles in order to match
the slide locking recess. This is to
insure that the barrel tang will enter
the locking recess of the
slide without binding the tang or locking
lugs as the barrel locks
up into the firing position.
c. When the tang is fitted to the recess
in the slide, start to
remove metal from the flat surface of
the tang in order to fit the
hood and lugs into the slide. Care must
be taken not to remove
too much metal. This fit should be as
tight as possible in order
to assure that a good fit will occur
when the slide and barrel are
in the firing position. A layout die
is recommended to fit the
tang squarely to the slide.
d. After the fitting has been made,
use an alignment gauge 8
inches x 0.4375 inches with a 3/32 inches
x « inches tip
inserted with the small tip to the rear
of the slide in order to
check alignment of the barrel with the
firing pin. If the barrel is
perfectly aligned, the small end of
the tip will enter the firing pin
aperture center and assure a center
strike of the firing pin on
the cartridge primer. If the barrel
locks in the slide too high for
the gauge tip to enter the firing pin
aperture, it will be necessary
to weld an appropriate thickness of
metal into the slide above
the barrel in order to get the proper
alignment of the firing pin
and barrel.
e. With a new barrel and bushing fit
into the slide, place the
slide with the barrel installed onto
the receiver, making certain
that the locking lugs on the bottom
of the barrel fit into the
recesses of the receiver without binding
on any side. If there is
rubbing on either side, make the necessary
adjustments to
assure a loose fit in the locking log
recesses. At this point
there must be a snug fit in the barrel
tang and hood. A snug fit
should also exist between the barrel
bushing and slide as well
as the barrel bushing and barrel.
f. Use a lug cutter, such as is available
from Brownell's, to cut
the locking lugs. The lugs must ride
smoothly onto the slide
stop pin, with the slide stop pin holding
the barrel snugly
against the top of the slide when the
barrel and slide are in the
firing position. After a tight fit has
been achieved, polish the
locking lugs with a high speed grinder
and suitable rubberized
abrasive tips. A Dremel tool works adequately.
Take extreme
care during the polishing to not polish
on one side more than on
the other. The lugs must be kept perfectly
level. Frequent
checks should be made using Dykem Blue
on the lugs to
assure perfect fit on the slide stop
pin. Continue polishing until
lockup is smooth but snug and resting
equally on both sides of
the lugs. At this point if the barrel
hood and tang are too tight,
remove a small amount of metal from
the tang with a very light
cut in order to permit a smooth lockup.
It is good practice to
use lapping compound to get a perfect
fit.
g. After this fit is obtained, check
the feed ramp on the barrel to
be certain that the feed ramp on the
barrel is forward of the feed
ramp on the frame by approximately 1/32
inches. This will
insure that the nose of the cartridge
will not hang up as the
cartridge is loaded into the chamber
from the magazine. Keep
the angle on the barrel feed ramp the
same as the ramp on the
receiver (approximately 33ø).
The barrel feed ramp includes
approximately « the lower diameter
of barrel ground on the
lower half of chamber end. The feed
ramp on the barrel must
not overhang the ramp on the receiver.
However, the feed ramp
on the barrel may be set forward of
the feed ramp on the
receiver as much as 3/32 inches. The
two feed ramps may be
checked by locking the slide to the
rear and looking through the
ejection port.
6. Fitting the trigger
a. There are two types of triggers
used on the U.S. Army's
National Match .45 pistols: the
standard Colt steel trigger and
the aluminum National Match trigger
found on the Gold Cup.
Each trigger comes in two different
length (long and short). The
aluminum long trigger is slightly
shorter than the long Colt
trigger.
b. Using a number 36 drill, drill
a hole in the trigger for the set
screw. This hole will be tapped
with a 6-32 tap. After tapping
the hole, install a 6-32 x «
inches Allen head set screw for the
trigger stop screw. After completing
this operation, check the
trigger in the trigger opening
of the receiver. Since most
triggers are oversized in their
width dimension, it is necessary
to remove metal from each side
of the trigger until the trigger
will fit into the receiver without
horizontal or vertical movement.
When this fit is achieved, the
next step is the trigger job, which
includes fitting the sear and
hammer.
7. Sear and hammer fitting
a. It is critically important that all
original angles be maintained
on the hammer and sear. The hammer hooks
are then cut
down to 0.0200 inches by using a thickness
gauge. Placing the
thickness gauge squarely on the hammer,
file the hammer
hooks down to 0.0200 inches using a
smooth mill file.
b. Check the sear and hammer for proper
engagement and
proper angles using a hammer and sear
mating fixture.
c. Polish the sides of the new National
Match sear so they are
smooth. Be sure the sear's sides are
free of burrs or rough tool
marks. Also polish the disconnector
and trigger yoke (bow) to
assure smooth operation when the pistol
is reassembled and
the moving parts are under normal working
pressure.
d. The half cock notch is cut on each
side of the hammer an
even amount, so as to leave the hammer
notch 0.1250 inches
wide and then the depth of the sides
of the half cock notch are
cut down to the base of the hammer using
a smooth mill file.
This leaves the full half cock notch
to catch the sear in the
event the hammer falls. This provides
complete safety on the
same principle as is produced in the
Colt factory for the .45
Gold Cup.
8. Trigger pull
a. Assemble the hammer, sear, disconnector
and sear spring.
Check for the desired break and weight
of trigger pull. The
trigger pull may be lightened by honing
a slight radius on the
point of the sear. To make a heavier
pull, increase the
engagement of the sear by increasing
the angle on the point of
the sear.
b. After proper operation and trigger
pull have been obtained,
adjust the trigger stop to have approximately
1/8 inches travel
after the break. This is necessary to
obtain the tolerances
needed for the disconnector to work
after each shot is fired.
c. Insure that the weight of the trigger
pull is within the limits
prescribed by N.R.A. rules and regulations
and still maintain
the required safety factors. The weight
of trigger pull varies with
each type of pistol used. Minimum recommended
weights are
as follows:
i. .45 ACP 230 FMJ (ball) 4 lbs. minimum
ii. .45 ACP wadcutter 3« lbs.
minimum
iii. .38 Super 2« lbs. minimum
9. Sights
Sights used on .45 and .38 Super target pistols are the micrometer
adjustable style. The Bo-Mar sight system is recommended due to its
durability and precise movement. The point of impact may be moved as
little as ¬ inches on the target. Install the sights according
to the
manufacturer's instructions and make certain the N.R.A. specifications
are meet for competition pistols. Rules vary from time to time and
the
latest copy of the N.R.A. rules should be consulted.
10. Common malfunctions
a. Failure to feed properly
i. In most cases the cartridge will
nose upward against the top
of the barrel hood and chamber. This
can be caused by the
feed ramp on the barrel having less
than the necessary angle or
the feed ramp on the barrel overhanging
the feed ramp on the
receiver. To correction this problem,
grind the feed ramp on the
barrel to a more forward angle and make
sure the barrel does
not overhang the feed ramp on the receiver.
Polish all surfaces
in order to remove all tool marks.
ii. Very frequently the magazine follower
is bent to an improper
angle or else the lips of the magazine
may be too tight. This
prevents the magazine from releasing
the cartridge in time to
allow the round to enter the chamber.
If the cartridge noses UP,
bend the follower DOWN. The correct
angle should be 70ø to
75ø.
b. Failure to chamber the round
This is characterized by the slide stopping
1/8 inches to 1/4
inches out of the full closed, battery
position. Correct this
problem by relieving the tension on
the extractor and/or
rounding off the bottom of the extractor
to permit the extractor
to cam itself onto the base of the cartridge
with greater ease.
c. Cartridge "stove pipes" during ejection
i. This malfunction is usually caused
by the recoil spring being
too strong (stiff) and not permitting
the slide to go fully
rearward, having the slide go fully
rearward but coming forward
too fast or because the ejector does
not have a good square
face. The recoil spring used for firing
230 grain hardball (full
metal jacket; FMJ) rounds normally has
29 to 33 coils. If you
find it necessary to cut down the recoil
spring, cut off only one
coil (some prefer « coil) at a
time until the problem is corrected.
ii. If the ejector is found to be round
or worn, file the ejector's
face square and maintain the original
angles. Sometimes it is
necessary to install a new ejector when
the pistol is firing .45
wadcutters or .38 Super. This is because
there are inadequate
recoil forces to move the slide completely
to the rear,
permitting the cartridge case to exit
the pistol in time.
d. Misfires
i. First examine the detent made by
the firing pin on the primer
of the misfired cartridge. If the primer
is not dented enough
there could be a broken firing pin,
burred firing pin or the firing
pin could be binding in the firing pin
retainer plate. Carefully
check all of these points.
ii. It is possible to have a weak mainspring
or the mainspring
could be hanging up in the mainspring
housing (due to a burr
on the spring or in the housing itself).
iii. Excessive headspace can cause misfires.
Normal
headspace is 0.0080 inches to 0.0120
inches and should
NEVER exceed 0.0120 inches. If the shooter
is using his own
reloads, examine his cases for proper
length.
e. Pistol fires full automatic
i. This can be caused by several things:
improperly adjusted
trigger stop (too close), too light
a trigger pull, disconnector too
short due to excessive wear or polishing
or the center leaf of
the sear spring is simply too weak.
ii. If the problem is traced to an improperly
positioned trigger
stop, readjust the trigger stop to permit
not less than 1/8
inches travel after the break.
iii. Make sure the trigger pull is not
less than the appropriate
value specified in item 8c. Increase
the trigger pull weight by
increasing the engagement of the sear
and hammer.
iv. If the problem is traced to the
disconnector, simply replace
it. Polish it before installation to
remove and burrs.
v. If the center leaf of the sear spring
has lost its temper and
will not longer hold its set, replace
the sear spring with a new
one.
11. Differences between .45 ACP and .38 Super pistols
a. While the pistols are generally built in the same manner, some
differences do exist. The .38 Super has a recoil spring composed of
softer 0.0330 spring wire.
b. The .38 Super extractor is specially designed and fitted to have
less
tension gripping the cartridge case.
c. The .38 Super extractor claw is deepened and shaped differently
in
order to cam onto the cartridge case.
d. The trigger pull on the .38 Super is set to 2« pounds.
e. Gold Cup type magazines are used in the .38 Super.
