MK19 Mod 3: US Ordnance Runs the Gauntlet

MK19 Mod 3: US Ordnance Runs the Gauntlet


By Dan Shea

Since 2016, U.S. Ordnance has been the sole supplier of the US Model MK19 Mod 3 and Mod 4 machine guns to U.S. military and OGA end users. In 2022, they were issued the NSN as sole supplier, with an IDIQ contract of up to $50 million. As we go to press, they are in first article testing on the contract, and we were allowed to participate in the testing, phase I. (Phase II will be reported on in the first issue of SADJ 2024, it’s an extensive live firing test).

MK19 Mod 3


  • Caliber: 40x53mm
  • Weight:  77.6 lb. (35.2kg) empty
  • Length: 43.1 in. (1090mm)
  • Width: 9.46 in. (240.4mm)
  • Barrel Length: 16.25 in. (413mm) (Removable)
  • Muzzle Velocity: 750-790 fps (230-240 m/s)
  • Effective Firing Range: 1,500m (1,600 yards)
  • Maximum Firing Range: 2,212m (2,419 yards)
  • Feed system: either 32 or 48 grenade belts in metal can, M16A2 link.

Since U.S. Ordnance received the NSN and contract, there are now over 186 parts inspections that must be accomplished. Each one must meet the military standards for production. There is also a protocol testing called for in MIL-G-70790 (AR), the Military Specification for Gun, Machine, 40mm MK19 Mod 3, which must be strictly adhered to and passed with government inspectors viewing the proceedings. In this article, we’ll review relevant first parts of the testing we observed. 

In section 3.3, gun sights and bore calibration are checked- the wedge optic mount on the right side in the MWO has to be perfect for calibration, which we did check. Then in 3.4 and 3.5, it’s an ammunition compatibility check to ensure all the various 40x53mm rounds will chamber and fire, done. In section 3.5.1 Proof Testing: “The machine gun shall withstand the firing of one M385A1 40mm cartridge without any evidence of part failure, deformation, or loosening.” Done. The M385A1 has a one-piece solid aluminum projectile with a rotating band, in an M169 cartridge case. The propellant is M2 (4.2g, (0.15 oz.)), the primer is an FED 215 percussion type. The ogive of the M385 series matches the shape of the M430/A1 HEDP projectile which has 45g (1.61 oz.) of Comp A5, a shaped charge with copper liner, and a pre-fragmented body. It’s just the ogive that matches, the M385 series frequently is indented at center, weight lightening to match the M430. The M385A1 uses M16A2 links only (the M385 can use either M16A1 or A2).
Rows of MK19 bare receivers in the process of getting all weldments done. Note the tracking papers – each part is tracked all through production.
While the receivers are still in the unfinished state, the dimensions are checked in every possible manner. Here, the receiver length is checked with a Trimos Mestra Touch height measuring instrument. This is one of the most accurate instruments that can be had in the market today. Mestra-touch has all the basic functions such as checking heights, depths, diameters and centerline distances, squareness deviation, angles and tolerance limits indication. In addition, the Mestra-Touch has a color touch screen and functions such as the two-coordinate system, programming of measuring sequences, statistical analysis of memorized values and display of environmental temperature. It can also record and convey the data to the computer system used in QC. Instruments like this are critical in tracking manufacturing process and especially, for government contracts like this one. The MK19 receiver is a difficult one to make, U.S. Ordnance has nailed the process, perfectly.
Once the receivers have been thoroughly checked, they go to Parkerizing; this is a three-step process. The first tank cleans the surfaces with a solvent solution, the second has the actual Parkerizing solution (a phosphoric solution), and is heated. The chemistry and temperatures in these tanks are critical and the contents are not mixed. The last process is clean water, that flows and cleans the solution from the surface and finalizes the finish. Finishes are up to 1-2 micrometers thick when done, depending on the spec.
After Parkerizing, more gauging is done before assembly starts.
Barrels are installed at the barrel station.
Bolt assemblies have been prepared, every part gauged, and assembled.
Final assembly is done at the production station. In section 3.6, Interchangeability, five guns were chosen, disassembled, parts mixed, then five guns were assembled from random parts, and gauging and testing were done. This was all a complete pass for the testing we did.

Section 3.7 Marking: Each machine gun and each part for which marking is prescribed shall be clearly marked in accordance with MIL-STD-130. Each receiver shall be identified with a serial number which shall be assigned by the procuring activity. The markings in this photo are the correct ones according to the MIL-STD. The barrel markings are as well, but parts like the barrel also receive a “PM” mark for “Proof” and “Magnetic Particle Tested” (See the M249 article in this issue for Magnaflux procedures).

Finished MK19 barrels waiting for assembly. As part of the MIL-STD, the grooves must be checked for height all through samples of the production barrels. Here, an extremely thin shim is cut cross-sectionally of the middle of the barrel, and the consistency and depth of grooves related to lands are checked, as well as finish depth. The cutaway barrel is for reference on the chamber and how the projectile is entering the grooves in the bore. Obviously, these are destructive tests and done on random barrels during the specification match testing.

MK19 pins waiting for individual review.

In Section 4.5.8 Trunnion Load, a. for First Article Inspection, this test shall be performed concurrently with the belt pull test. B. Mount a Quartz Force Link Cell Kistler Model 9362 with a Charge Amplifier Model 504E and a Filter Model 545A (Or Equivalent) directly below the receiver, below the locking pin, integral with the mount and in alignment with the receiver buffers. C. Record a time -load trace of recoil using a Honeywell Visicorder Modl 1858 with a TCD (tape compatible differential) Amplifier Model 1887, or approved alternate equipment. D. Trunion load forces are to be measured at the mounting point. The last three (3) rounds of the belt fired shall be discounted. The mount shown here is a special mount custom made to the government specification for the test. The Kistler Force meter is a very expensive and sensitive piece of equipment, yet it is built to handle greater recoil forces than it will measure in this test. The reason for testing during the belt-pull test is based on finding variations in the side weight of the belt, and as the belt lightens the forces will change. This data will be valuable to see the consistency of the construction. After this first article test, the trunnion load tests will be less frequent but based purely on single rounds fired.

40x53mm ammo piled up in anticipation.

In the next issue of Small Arms Defense Journal, we will be joining U.S. Ordnance for the full-tilt firing part of the test. The ammo is lined up, the testing fixtures are ready, and we’ll be doing cadenced endurance testing, temperature testing, belt-pull, cyclic rate of fire, angle of fire, firing modes, accuracy, reliability, and a host of other tests. The full trunnion load test will be done several times through the testing. Be sure to join us!