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.

3.  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 b.  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.
c.  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.
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

1.  Failure to feed properly

a.  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.
b.  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.

2.  Failure to chamber the round

a.  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.

3.  Cartridge “stove pipes” during ejection

a.  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.
b.  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.

4.  Misfires

a.  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.
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).
b.  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.

5.  Pistol fires full automatic

a.  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.
b.  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.
c.  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.
d.  If the problem is traced to the disconnector, simply replace it. Polish it before installation to remove and burrs.
e.  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.

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