Casing Review

37mm and 40mm Aluminum with 9mm Casing

Smokeless Launching System


By GROG   Copyright 2010 3LC Productions

Recently I was contacted by Scot Pace concerning some new reloadable aluminum casings he had developed. These casings use a simple 9mm Luger casing, in place of any crimped or rolled blank for the lift charge. The casings are press fit into the screw off base of the casings. The 9mm Luger is very easy to reload and can hold up to 9 grains of Bullseye. (although I do NOT recommend loading that much smokeless into one, ever.) The casings use a simple metal  “wad” to close off the single vent hole on top of the high pressure chamber, inside, where the 9mm casing goes. Because, the base of the casing actually unscrews, so you can use a number of different length casing sidewalls, or even replace them if they get damaged! They are also easy to make sure you get a nice RTV seal on your projectiles. Scot offers many options when it comes to his casings. Some of those options will be covered in this review.


One word on these casings… Awesome!



37MM Casings


Scot sent me a variety of these casings, in 37mm and 40mm, in different lengths for testing and evaluation. The kits he will offer come with some 9mm Luger brass and a simple reloading tool set to use, including an aluminum base that you sit the 9mm brass in, and a small punch to punch out expended primers. Simple, and easy, which is the best these days. The sidewalls on some of the 37mm selection are VERY thick. .125” as a matter of fact. No, that is not a typo. The bottom of the sidewalls are threaded inside, and the high pressure chamber is threaded on the outside, with either two flats you can use a spanner wrench to help open, or with three pin holes around the base for using a pin wrench. The base is .995” tall, and the top .515” is threaded. The aluminum around the 9mm Luger casing on the 37mm is .565” thick. No issues with pressure here. The casing OD on the 37mm is 1.490”, and the ID is 1.240”. These casings are made with the reloader in mind!


The sidewall length on the 37mm casings provided to me was 3.840” tall, but these can be cut to any conceivable length you might need or desire. The outer surface of the casing sidewall is lathe turned. The rims provided were modified by myself to fit in my M79 with 37mm barrel, but Scot can do a stepped rim to fit any launcher.


Bases come in both 37mm and 40mm versions, and include a low pressure chamber milled area!


37mm Casing Test #1


I prepared three of the supplied 37mm casings by cutting the sidewalls down to 1.500” I also prepared three 37mm test projectiles, designed for casing reviews. They are solid, M406 ogive shaped, and weighed 40-45 grams, are marked with the weight, and seal nicely. I loaded three 9mm Luger casings with Remington 1 ½ small pistol primers, and 4 grains of Bullseye Pistol Powder, and one 38cal copper disc to cover the venthole. The discs fit very well, and I used a large punch to seat them in the chamber. The more powder you can get to burn inside the high pressure chamber, the better your powder will perform. If your powder ruptures your venthole disc too soon, some of your powder will be lost out of the venthole before ignition. The copper discs were .010” thick for this test. The 9mm casings fit very tightly into the casings, and you may need an arbor press to seat them fully. I used a large flat punch to seat mine.


I sealed the test projectiles inside the short casings with black RTV sealant, and allowed them to set overnight to cure the RTV.


The test casings were fired using my M79 with 37mm smooth bore barrel in place. All three casings fired with no malfunctions. The test projectiles were all launched 200 meters effectively, using the M79 sights aimed at 200 meters. The casings were then disassembled and checked for problems by visual examination and measurements. No problems were observed. The 9mm Luger casings were easily removed from the 37mm bases, and did not appear to have any “belling” or cracks. The primers had no overpressure indications. 9mm Luger casings did not back out of the 37mm bases at all.



Close-up of the base interior showing the high and low pressure chamber, threads, and rim. Notice the side of this casing has been milled flat to accept a spanner wrench to allow for easy disassembly.


37mm Casing test #2


I then prepared another test casing, to test a maximum load with overpressure. You have all heard the standard “don’t do this at home” warning, this is one. I loaded one 9mm Luger casing with 9 grains of Bullseye pistol powder. I also created a test projectile weighing 75 grams by adding lead shot to the mold and molding the shot into the base of the projectile. For this test I lathed the side of the projectile down so it fit tightly into the longer sidewalls provided by Scott. I fully expected this would test the limits of this type of casing, and the threads provided. On firing, the recoil was quite substantial, and the projectile was not found or seen after launch. I’m glad I used my beefy M79 to test this casing… The casing was removed from the launcher after firing, and checked for any type of failure or stress, belling, or over-pressure indications. None were found on the aluminum casing itself, except for a very small amount of belling around the venthole that would not affect the usefulness of the casing. The 9mm Luger casing also did not show any stress or cracking. The Remington primer, however, was smashed flat against the rear face of the firing pin retainer, and had the machining marks from the M79 firing pin retainer on it. I do not recommend a 9 grain load of Bullseye in these casings, as that load would most likely break less substantial launchers on the market.


Top view looking into the base


37mm Casing test #3


Scot provided me with two of his 37mm stepped rim casings, which can be used in either 37mm or 40mm launchers. One of the casings had an internal low pressure chamber lathed into it like the M212 casing, with similar sized venthole, the other had a smaller venthole, with a cupped low pressure chamber right above the venthole. (Photo below) I prepared both by loading the 9mm Luger casings with 4 grains of PB and 5 grains of PB respectively. I used a .016” aluminum vent plug in the 212 style low pressure system, and a .010 copper vent plug in the other. Using a 37mm test projectile weighing 39.4 gram projectile. The aluminum vent plug with 5 grains of PB sent the projectile 25 yards. The copper vent plug with 4 grains of PB sent the projectile 75 yards. Don’t use aluminum for vent hole plugs, except in the new high performance 37mm Scot is developing! J

Scot's 37mm short casings interior.jpg

Two 37mm Stepped rim casings with different pressure system designs


37MM Casing test #4

I prepared the same casings with the same test projectiles again, this time using the copper .025” thick wad in both. I used 8 grains of Bullseye Pistol Powder in both casings as a pressure test. Both rounds functioned. The 212 like casing projected the test projectile 150 yards. There was no pressure issue observed with this casing. The smaller venthole casing also launched the projectile 150 yards, however there was a pressure issue. The 9mm Luger casing was split in half right above the base area, and the top of the casing stuck in the 37mm casing. The rear of the 9mm Luger casing was flattened against the M203 breech face, the primer was completely flattened. Do not use large powder charges with smaller venthole designed casings. I loaded another small venthole casing using the same test projectile and copper wad, only this time I used 4 grains of Bullseye. The projectile was launched 150 yards again. Same results, with less powder, and no pressure issues.


Scot provided me with 6 of his new, longer 37mm casings, which also use the same 9mm Luger propulsion system. These casings had a straight knurl in two places on the casing sidewalls and had the thick .120” sidewall. The outside of them is machine finished, the inside is straight wall extruded except the interior threaded portion that screws into the base. Here is the casing sidewall:

Scot's 37mm long casing sidewall 1.jpg


The interior of the casings:

Scot's 37mm long casing sidewall interior 2.jpgScot's 37mm longer casing sidewall interior.jpg



40MM Casings


Scot also provided me with 12 40mm casings, made to the same dimensions as the nylon M212 casings, however, these are aluminum, use the 9mm casing propulsion system, and have a screw apart body! At first appearance, these are impressive casings. They have a straight knurl on the side, to aid in removing the base. The height is 1.80”, OD is 1.620”, ID is 1.525”. Perfect to load those M781 zincs! They use the 9mm Luger casing for reloading. The interior of the sidewall is machined as well, to fit perfectly on the base, and to also provide the low pressure chamber like the M212 nylon casing. There are three holes in the side of the base. These are for inserting a simple pin wrench. This will allow you to open the casing when the threads become dirty from multiple firing, or when the metal expands and contracts due to temperature changes. Scot also makes a version with two flats on opposite sides of the base for a spanner wrench. He can make either style, to your desire.


Scot's M212 sidewalls 1.jpgScot's M212 sidewalls 2.jpgScot's M212 sidewalls 3.jpg



Interior view with M781 zinc installed:


Notice how you can load the projectiles and bases separately. This makes it very easy to get a nice seal on your zincs or other projectiles when using RTV and other sealants for projectile seating. No more guess work or blind gluing. Simply place the finished projectile in, throw a bead of RTV all around the bottom between the zinc and the casing sidewall, and you have a perfectly sealed projectile. It will also dry RTV faster as it is exposed to the outside air.



Long and short casing sidewalls, loaded 781s, and bases…


When I receive casings for testing, the first thing I normally do is stamp them on the bottom with a number. This number is then recorded in my log book, with the load data of that particular casing, including powder charge, powder type, type and weight of projectile used, type of wad and thickness used, and results of the test. This makes it simple to track and test multiple loads with different projectile weights, and keep track of a casing throughout their life.


40MM casing test #1


I loaded 11 of the 12 40mm casings provided. To get accurate results, I used factory loaded, never disassembled  M781 orange dye filled blue plastic windshields with never fired zincs pulled from some M781s bought from Clyde’s Armory that were off spec (brass seated too low for firing pin to engage). They were cleaned of old RTV, inspected, and prepared for firing.


I reloaded the 9mm brass with new Remington 1 ½ small pistol primers, and the below listed loads. I placed a foam ¼” thick 9mm cal sized wad into the 9mm casings after I loaded the powder, for the simple reason of keeping the powder in the casing in case I bumped the reloading table J. I also purchased an assortment of metal sheeting in different thicknesses and types for closing disc testing. The closing disc is important for proper functioning of the high/low pressure chamber. If the cardboard wad, or metal wad gives way before the powder in the lift charge burns, you will get very poor performance from your casings, from not all of the powder being burned. If you notice un-burnt grains of powder inside your casings after you fire, it is because of improper wad, or too powerful of a primer being used. Never use magnum pistol primers with 37mm and 40mm casing reloading.


I used black RTV to seal the projectiles into the casings. I found it VERY easy to unscrew the casing sidewall, and RTV the projectile in place. I used a similar amount to the standard M781 loading, making sure that the sides of the zincs were evenly coated, and that it extended into the casing sidewall. This procedure is VERY difficult with nylon casings, especially new ones that don’t have the vent hole drilled. The air is trapped in the low pressure chamber, and can pop your projectile out while you are waiting for it to dry. With these casings, that is not an issue.


I used to put the RTV on in this manner, to avoid trapped gas. You place your projectile in, then give it a turn to spread the RTV. You don’t need to do this with these casings. Just flip them over and seal from the bottom. You can also limit the amount of RTV you use to seal them.



Numbered bottoms and casings being prepared for loading



This photo shows the interior of the casing bottoms. You can see the quality machine work involved in producing each casing. The low pressure chambers are even lathed out to proper specs! You can also see the straight knurl on the casing sidewall, and the flats milled into the sides to assist in unscrewing the bottoms from the sidewalls. Another good thing about these is the flexibility to be able to buy a number of bases, then assorted length sidewalls for all sorts of different reloading!


Here is the loading data, and test results for the casings tested:


Casing number   Wad used              Powder used           Aiming point                      Results of test

1                           .015” Brass           4 grains PB           100 Yard target       Good power, 97 yard impact point

2                           .016” Aluminum    4 grains PB           100 Yard target       Very poor power, 20 yard impact

3                           .010” Brass           4 grains PB           100 Yard target       Mid range power, 75 yard impact point

4                           .025” Copper        4 grains PB           100 Yard target       Fantastic power, 100 yard impact point

5                           .015” Brass           5 grains PB           100 Yard target       Good power, 95 yard impact point

6                           .016 Aluminum      5 grains PB           100 Yard target       Very poor power, 30 yard impact point

7                           .010 Brass             5 grains PB           100 Yard target       Mid range power, 75 yard impact point

8                           .025 Copper          5 grains PB            100 Yard target      Fantastic power, 104 yard impact point

9                           .015 Brass             5 grains Bullseye  100 Yard target      Fantastic power, 110 yard impact point

10                         .016 Aluminum      5 grains Bullseye   100 Yard target     Poor power, 75 yard impact point

11                         .025 Copper          5 grains Bullseye   100 Yard target      Fantastic power, 125 yard impact point


From the above tests, the thicker the closing wad, the better the performance of the casing. After firing all casings were checked for over-pressure problems, or other problems with the results below:


1.  Primer appears normal, no over-pressure indications, measurements remain the same from pre-fired condition.

2.  Primer appears normal, no over-pressure indications, measurements remain the same from pre-fired condition.

3.  Primer appears normal, no over-pressure indications, measurements remain the same from pre-fired condition.

4.  Primer appears normal, no over-pressure indications, measurements remain the same from pre-fired condition.

5.  Primer appears normal, no over-pressure indications, measurements remain the same from pre-fired condition.

6.  Primer appears normal, no over-pressure indications, measurements remain the same from pre-fired condition.

7.  Primer appears normal, no over-pressure indications, measurements remain the same from pre-fired condition.

8.  Primer appears normal, no over-pressure indications, measurements remain the same from pre-fired condition.

9.  Primer appears normal, no over-pressure indications, measurements remain the same from pre-fired condition.

10.  Primer appears normal, no over-pressure indications, measurements remain the same from pre-fired condition.

11.  Primer has very slight pressure indications, nothing severe, measurements remain the same from pre-fired condition.


To duplicate the military loading of the M781 practice round, I recommend using the .025” copper closing wad, with 4 to 5 grains (as measured on a reloading scale) of PB powder, or 4 to 5 grains of Bullseye pistol powder.


40MM Casing test #2


I prepared four muzzle blast rounds for the longer 40mm casings provided by Scot. I used inert orange powder for this test, loaded into a thin walled cardboard tube cut partially lengthwise and with a ½” thick wooden wad base plug. I loaded 4 of these projectiles into Scot’s longer sidewalls, and used RTV to seal the bottom of the wood wad to the interior of the casing sidewall. Perfect seal. I used the 40mm bases he has developed that mimic the M212 casing, and that screw off with a pin wrench. Here is a video of one of those casings being fired at the camera:

40mm Muzzle blast test fire video


To purchase Scot’s casings, please visit his website here:


Additional tests are ongoing with some specialty casings Scot produces. Results and additional video links will be provided as tests are completed.




Copyright 2010

 3LC Productions