37MM CUP, Cap, CASING, and Bushing Review


By GROG   Copyright 2010


This review will be on four items from the same company, American Specialty Ammo. Having this forum, I have learned a lot over the years. One of the things that has become readily apparent is, there is a great lack of reloading components, professionally and commercially produced, for the 37mm and other sizes of launchers. The problem was identified, now here is the solution!

I was contacted by the owner of ASA, Chris Reed. He was willing to take on the task of producing items for the reloaders like us, but needed some help with design and molds. I was happy to assist him with his work. Chris had the casings, and needed internals and projectiles developed for them. The work began…

The first project we started on was a reloadable projectile carrier that could be used with a multitude of different types of payloads. Something that would easily replace flimsy film cans, and increase the range of 37mm launchers. I gladly took on the job of designing such an item, and entered into a licensing agreement with ASA concerning this. I do not make money on any of the individual sales of these items. I make the molds, and the products are licensed for use by me, but as far as construction (making them) and profits go, it all goes to ASA. I find this important in maintaining objectivity when reviewing these items for my membership and others. Here is what I came up with for you and them, the 37mm CUP, Cap, and Bushing.

First, a word on Chris’ casings. They are 37mm, and are black powder propulsion system casings. The sidewalls are .075” thick above the base. They are available in two lengths at the present time. The taller length is 3.275” from the base to the top, with a payload area that is 2.40” long and has an ID of 1.370”. The rim is .100” thick, and has an OD of 1.690”. The OD of the casing is 1.520”. The bottom of the casing is thick… .300” thick to be exact. The shorter casing is 2.255” tall, and has a payload area that is 1.330” deep, and has an ID of 1.370”. The casings use a #209 shot shell primer as an ignition source. With these dimensions, I started designing a multi-purpose projectile that we could all use.

The first thing I noticed this casing needed was an internal powder bushing. Something cheap, and reusable. I observed that the interior of the casing is stepped in around the interior base, the sidewall at the base is .135” thick. This extends upward for a distance of .325”. This alone is capable of holding quite a large amount of black powder. Possibly being unsafe for the novice reloader, who might attempt to pack that area full of powder… Big, bada, boom. I designed the powder bushing to reduce the powder area, and to hold a maximum charge of 80 grains of fffg black powder. This amount of black powder is quite sufficient to propel a payload a very good distance, and still maintain a safety factor. The design of the bushing has some ridges on the outer surface around the top. This is to provide a nice seal for RTV silicone. The bushing also concentrates the black powder right over the primer. The interior sides of the bushing are angled up and outward to allow the force of the lift to be evenly distributed around the base of the projectile. Here is a cut-away photo of the casing with bushing installed:


The bushing in the above cut-away photo is black in color. You will notice how it angles down toward the primer hole, and how it has space on the outer surface for RTV.

The 37mm powder bushing is used in ASA casings to concentrate black powder or BP substitute over the center of the primer. The bushing is RTV’d in place prior to using the casings, and allowed to cure overnight. I recommend placing a bead of RTV in the base of the casing, on the bottom outside, and another thin bead on the top of the rim area inside, then using a pencil to place the bushing into the casing, seating it, and forcing the extra RTV out. This will provide a good seal, and insulate the bushing from the shock of black powder lift charges. The bushing is designed to hold 80 grains (to the level top) of fffg black powder. This makes reloading very easy. Drop in your black powder until it is even with the level of the top of the bushing, and you have 80 grains. The CUP sits right on top of the bushing, and seals your powder in. The cap fits on top of the CUP, and the whole round can be sealed for use at a later date. Here is a cut-away photo of the three pieces, as they can be placed inside the casing:


In this photo, the cap is tan, the small cup is red, bushing is green. You can see how the parts fit together inside the casing. When the cap is placed

In this manner, it is for a contained payload like a smoke burst, or star burst munition (using a fused cup). The cap is glued into the CUP to provide pressure for burst. The payload cup can be secured in place with a small amount of RTV around the base of the cup, or hot glue around the top cap.


The 37mm CUP is a multi-functional projectile that can be used by both registered and un-registered launcher owners. The CUP is capable of being fused for pyrotechnic payloads, as well as un-fused, for buckshot, flechettes, and CS/OC powders. The CUP is designed to be used in ASA’s own black powder casings, but can be used in other casings as well. All reloading information provided by ASA details instructions for reloading their casings. The CUP has three integral gas check rings lathed into the base. The taller CUP has another gas check half way up the body, which can be used to cut the CUP into the shorter version. The sidewalls of the CUP are nice and thick, and the base is also thick. They will hold any payload securely. The ID of the taller CUP is 1.170”, and is 1.320” deep. The short CUP ID is also 1.170” and the depth is .700”. This will hold plenty of buckshot, or flare composition for a distress signal.


In this photo, you can see the longer ASA CUP with three lower gas checks, and one mid length gas check. If you score this cup with a razor

Knife at the upper gas check, you will make a short CUP out of it. If desired, you can add a wrap of tape to make the projo fit tighter in your

casing. It is not needed however, and will do little to improve performance.



In this photo, you can see the short and tall versions of the CUP and a tall casing. All available from ASA.

The 37mm Cap is a specially designed cap that is made to be used with the CUP. One side of the cap fits into the fused CUP, and can be secured in place with super glue for pyrotechnic payloads such as smoke burst, smoke marker, and star clusters. The cap is also used with flechette and buckshot rounds by using the opposite, larger OD side down, which does not fit inside the CUP. This side of the cap fits inside the casing, and rides on top of the CUP until it is ejected on firing. The cap is hot glued in place around the casing sidewalls when used in this manner. Here are some additional cut-away photos:


In this photo, you can see the longer CUP with the cap placed with the ASA logo down. The cap is not glued to the CUP when used in this

configuration. Use this method when loading flechettes, rubber sting balls, CS and OC powder for muzzle blast, and similar types where you

want the payload released shortly after leaving the barrel of your launcher. To seal this projectile in, use a bead of hot glue around the top of the

cap, in the narrow space between the top of the cap and the casing. Use hot glue sparingly in this instance. Just enough to keep the projo in!



In this photo, you can see the small CUP used with the cap in the glued position. This is a taller casing, with the shorter CUP. Use this configuration for ariel flares,

ariel smoke burst signals, ground marker flares, and items which require a small payload chamber. Do not use hot glue or any other type of glue on top of the cap when using this configuration. To seal this projectile, use a small bit of RTV on the outside base of the CUP, to seal it to the top of the bushing. Allow to dry overnight before firing.



In this photo, you can see the small CUP, with cap and bushing. This type of munition makes a fantastic signal flare, and can be sealed and waterproofed

for survival situations.



In this photo, you can see the cap is reversed. This configuration is used for buckshot types of munitions where the cap is desired to

allow the payload to escape the CUP after leaving the barrel. Do not seal the cap to the CUP in this configuration. You want the two to separate

when fired. Seal this type of payload in the casing by using a small amount of RTV around the base of the CUP and top of the bushing, and also a small

amount of hot glue around the top of the cap and casing, on the ledge provided by the cap.



In this photo, you can see a 40mm M576 carrier with orange buckshot cup, and an unloaded tall CUP and loaded short CUP. This is done to

show you the difference in payload capacity of the CUP when compared to real military munitions.



In this photo, you can see the amount of shot the real M576 buckshot carrier holds. Now, here is a photo of how much the short CUP holds:






For testing and munition development, I prepared four shot rounds first, using short casings, short cups, and loaded them with 80 grains of fffg Clean Shot black powder substitute. Here is a photo of the rounds loaded:


As you can see from this photo, each round carries a substantial shot charge. You can also see the space on top where the cap will fit, logo side down,

to seal these rounds for firing.


All four rounds were taken to the range for testing. The launcher used was my M79 with 37mm smooth bore barrel. Range fired from was 15 yards. The target board is 4’ high by 2’ wide. These are the extra large targets. Here are the targets as hit:


First photo shows target with all holes patched pre-firing. I use “Shoot-N-C” targets which allow you to see impacts, as well as a backer of Tyvek.



Here is the first shot. The shot hit the target so hard, it blew the sticker patches off the larger bullet hole! Notice the tight, level shot pattern.

The results of this first shot are better than I had hoped for. You can see the impact point of the CUP at the top left of the photo. The backer is

a sheet of ½” thick treated plywood. As this was the first shot with the M79 37mm barrel, some sighting adjustments were made.



Here is the second shot fired. You can see the pattern remains the same, level, with another CUP impact mark on the left lower side of the 8 ring. The target

board is 2’ wide, by 4’ tall. Notice how the shot pattern goes from one side of the target, to the other!


Here is the third shot. Once again, the shot pattern is very well defined, from the left side of the target, to the right. Nice tight grouping of a

large amount of shot. As you can see, even the small CUP holds a LOT of shot!




Here is the final photo, showing all 4 rounds fired. The last round hit at the same location as shot #3, perhaps a bit higher. You can see how all four shots

had the exact same pattern spread, from left to right, as well as the same concentration of shot between rounds.


I next moved on to the pyrotechnic tests. I loaded up two fused short CUP and two fused long CUP rounds with Ninja smoke burst mix. Using 50 grains of fffg Clean Shot, I fired all four rounds on the target range. The rounds functioned perfectly, and burst at apogee, approximately 300-400 feet straight up. The increase in mass of the larger CUP did not affect altitude to a great degree. All four rounds provided very adequate signals, visible for quite some distance.


I prepared and tested all rounds as written in the reloading guide provided by ASA on purchase of their reloading materials. The guide was prepared by me, and all rounds were found to be suitable for the purpose for which they are intended. Remember, do not use explosives in ANY 37mm or 40mm round. These products were designed to be safe for normal use as outlined in the reloading guide provided. Any deviation from these instructions could result in injury or death. Drop by and read the safety page before constructing any 37mm or 40mm round.

Copyright 2010

 3LC Productions