Gauging and Services

Recently, someone asked me why Small Arms Repair Technicians service weapons. I answered with a laundry list of reasons. The first reason that always comes to mind, due to being in the military, is safety. Gauging is the main way to ensure that no dangerous issues are seen. Then came the main reason, and the one that gets me up in the morning each day to go to work. That reason is to keep that weapon fully mission capable, or in my terms, keep it functioning to the best of its ability.

In doing that we are not only helping the weapon but the Soldier. Before I continue, in case you’re wondering: Yes, the Army spelled this as "gaging" and "gages" since forever ago, however, the recentlypublished M16/M4 Unit and Direct Support Maintenance Manual (Army Technical Manual 9-1005- 319-23&P) has since changed the spelling to "gauging" and "gauges." Annual gauging is done to prevent catastrophic failures. This is your usual headspace, barrel erosion, barrel straightness, and other gauges.

There are two tolerances that we look at for most gauges and that is the warning and reject specifications. If a weapon passes the warning line but does not pass the reject, that weapon is good to train with in the States but not to deploy. If it fails both the warning and reject, it is immediately dead-lined and cannot be fired until repaired. While gauging is as simple as putting an object into another object, specifications can change a lot due to type of equipment and ammunition.

For instance, M240-series machine guns have different gas port erosion gauges depending on if it’s a short or long barrel. Also, the Army has adopted the new ammunition M855A1. With new ammunition comes new wear limits. As with anything, it’s important to stay on top of information when dealing with a strict entity such as the military. Services are where a well experienced firearms maintainer makes their money. Within the Army there are two manuals used to go over inspections on weapons.

There is a -10 and a -23&P. The -10 is the Operator’s Manual, meaning that the operator of the weapon has access to the manual and should be inspecting according to that manual’s inspection list before and after putting the equipment into operation. The -23&Pis the Unit and Direct Support Maintenance Manual, directing the higher echelons of maintenance and includes National Stock Numbers (NSNs) for parts.

The -10 Operator’s Manual is a very short, basic inspection that hits some of the more common deficiencies found on that type of weapon. The -23&P Unit and Direct Support Maintenance Manual goes much more in depth. While going step by step from Far

M4/M16 Bore Erosion, M4/M16 Barrel Straightness, M2A1 Firing Pin Hole, M2A1 Oil Buffer Rod, M2A1 Headspace, M2A1 Master Headspace, M4/M16 Firing Pin Hole, M4/M16 Firing Pin Protrusion, M4/M16 Headspace, M240 Firing Pin Protrusion, M240 Headspace, M2A1 Firing Pin Protrusion, M240 Bore Erosion, M240 Throat and Muzzle Erosion, Trigger Pull, M249 Barrel Erosion, M249 Headspace, Spring Lengths and Specs Tool, Mk-19 Bore Constriction, M2A1 Bore and Throat Erosion, M249 Firing Pin Protrusion. 56 ruptured cartridge removed with a 7.62 Ruptured Cartridge Extractor Tool from a M249 barrel during a gauging and services trip.

The Headspace Gauge failing to seat inside the barrel is a clear indicator of a ruptured cartridge. a manual is nice, it will never replace someone with experience and knowledge to see the little but important things or things outside the maintenance scope. Knowledge on maintenance is important, however, knowledge on how the operator is employing that weapon is just as important. For instance, often we will have optics and accessories mounted on the weapons when we are gauging and servicing.

Ultimately our end goal is to give that customer, or Soldier, the best product and experience we can while still making sure that they are falling in line with Army guidance and treating the weapon properly. Part of delivering that product and experience is working with them and their attachments. We often make sure that an attachment is mounted properly and to note where it is mounted if we have to remove or not remove it.

One example, many Soldiers will tie down their M68 Close Combat Optic (CCO) with para-cord and wrap it under the gas tube. As the weapon gets hot the gas tube heats up, melting the cord. So now you not only have to replace the gas tube due to damage but will probably have to retie down the optic as well. Also seen with the CCO, if mounted on the M4 we will see CCO mounts without the correct spacer on the mount.

While that is not necessarily our maintenance area, it is part of the weapon system and due to our knowledge and experience we are able to help the Soldier out with Far

Soldiers often remove the castle nuts and endplates to install their own endplate with a quick detach mount. The wear on the castle nut spanner spacings is an indicator that a Soldier may have removed the nut with their own wrench. the whole system including accessories, mounting systems, etc. Providing the higher-than-operator level inspections each year is so important.

Being able to get eyes on every weapon within the state each year shows us where we may need to focus on outputting more information or where we can feel comfortable and confident with certain units. Not only that, servicing the weapon each year actually helps the government save money and time. Think about this in civilian terms. Just like a car, guns have a preventative maintenance schedule.

Glocks, for instance, have suggested round counts for replacement of each individual piece to ensure zero catastrophic failures. This can be due to wear, bending, or cracking. The Army doesn’t necessarily keep those round counts so we are there to inspect and replace when we see those same issues arise from wear, bending, and cracking. If we replace these parts before catastrophic failure or before apart affects another it can save us money on ordering parts and time on working on the weapon.

As I stated in my previous article, we have seen a massive positive correlation between annual inspections and a lower amount of deficiencies found in the years after. To give you and idea how this works, I’ll use a Colt-manufactured M4 with Knight’s Armament Company M4 Rail Adapter System, B5 SOPMOD stock, and Ma Te c h Back-Up Iron Sight as an example with a maintenance and functioning checklist that allows operators to fully inspect their weapon while not disassembling anything beyond -10 (operator) level.

Clear the weapon using proper safety procedures. Inspect the externals of the weapon from front to rear. On the upper receiver assembly, start with the compensator. Twist it for movement as it should not move. Verify the three ports of the compensator are on top and centered. With the front sight base, inspect it for any bends or wear. Twist for movement, it should not move. With the barrel, inspect the inside for abnormal obstructions. Twist for movement, it should not move.

With the Rail Adapter System, inspect for burrs and cracking. Verify the screw and retaining clip are installed. On the upper receiver, function the ejection port cover for proper opening and closing. Verify the retaining clip is installed on the ejection port rod. The sight needs to be verified that it is tight and in the correct slot on the rail. Function the aperture for proper tension and the windage and elevation knobs, listening for clicks and seeing movement.

With the lower receiver assembly, verify the end plate is installed and staked to the castle nut. Twist the castle nut for movement, it should not move. Function the buttstock for movement and retention. Inspect it for cracks, verifying the sling swivel is installed. Twisting the sling swivel should not move. Field strip the weapon. With the bolt carrier group verify gas tube alignment and that the forward assistance functions the carrier.

Verify the extractor spring and buffer are present in the bolt and not bent or broken. Inspect the bolt’s locking lugs for cracks or breaks and the firing pin tip for breaks. Check that the gas rings are present and perform a gas ring wear test. Inspect the bolt for pitting, wear, and abnormal obstructions. Function the ejector with a punch, verifying movement and that no crunching noises are heard, and that the ejector is flush with rim of bolt. With the carrier, inspect for wear, cracks, and pitting.

Check the carrier key for proper staking and inspect for dents. Pull on the carrier key, it should not move. Inspect the firing pin retaining pin for wear and bends. Check the visible internal structures of fire control group, looking for wear. Verify the springs in the lower receiver are installed correctly. Inspect the recoil spring for bends or damage and that it is of proper length. Reassemble. Lubricate all lubrication holes and perform a proper function check including with an empty magazine.

The main gauging checks performed by a Tech include headspace, firing pin protrusion, firing pin hole, barrel erosion, barrel straightness, receiver pin holes, and trigger pull weight. None of this detail will surprise a working gunsmith but a Tech’s job is to make sure Soldier’s weapons are receiving the preventative maintenance they need to be reliable for training and combat. AG