What’s a Medium Caliber Cartridge doing on a website primarily dedicated to small caliber arms and ammunition’s? Well, we all have to have dreams don’t we? Truthfully I was introduced to this cartridge through my love of aviation. The A-10, which has become an iconic close support aircraft, has always been one of my favorite aircraft to study. If I ever had the opportunity to fly one, or sit in the cockpit, I would be beside myself. So naturally you combine my love for aviation with my passion of ballistics and naturally I would gravitate toward the 30mmx173 cartridge.
A Brief History in Aviation
For those living under a rock, or who do not have much to do with aviation, the Fairchild Republic A-10 Thunderbolt II, AKA A-10 Warthog, was the first aircraft that the United States designed from the ground up to be a close air support aircraft. Previous aircraft were aircraft that were modified airframes designed to serve the role.
The concept of close air support aircraft (CAS) dates back to World War 2, where numerous types of aircraft on both the allied and axes sides, were outfitted with medium and large caliber arms in order to provide anti vehicle, including anti tank support for infantry on the ground. Success of these early attempts were mixed, some aircraft adaptations performed better then others, and given the newness of the tactic pilots were often trained when out on mission, rather then having role specific training prior to entering the battle field.
The A-10 was developed from the ground up to be a robust aircraft that can take a few licks and keep on fighting. Aside from the GAU-8/A which is an impressive piece of armament in it’s own right, the aircraft boasts numerous design features that increase the survivability of the aircraft and it’s pilot during the performance of it’s missions. This includes a titanium “Tub” which sides around the cockpit and protects the pilot from most small arms and some medium caliber weapons. Four independent and self sealing fuel tanks, triple redundant control systems, and a resilient airframe that allows the aircraft to lose half a wing, an engine, and half the tail and still keep flying.
It seems that the A-10 is always on the chopping block when it comes to defense spending. There seems to be two competing lines of thought in the military, the first wanting to reduce or remove equipment with single mission capable fighters in favor of adaptable multi mission capable fighters such as the the F-35. These fights seem to play out every 2 to 4 years but each time it seems the A-10 pulls through and receives the relevant upgrades and budget to remain in service. At this time it is projected to remain in service until 2040.
Unfortunately the military is not in the habit of selling it’s surplus aircraft to the civilian market. On retirement aircraft go to large boneyards full of aircraft that make up the militaries reserve fleet. The concept being, should there be a war that seriously stresses the United States ability to keep up with aircraft production, this reserve fleet can be pressed into service quicker then new production aircraft. After spending years in the boneyard, aircraft are eventually marked for scrap and are sent to the scrap yard.
Even if you were able to source a demilitarized A-10, the per flight hour cost is reportedly $7,000 per hour. A Lear Jet 24, which is a twin engine jet about half the weight of a A-10, has a reported hourly flight cost of $2,800. For reference a Cessna 172, flight hour cost is about $100 to $200. It’s hard to directly compare flight hour costs, as I believe military aircraft are held to a high standard of maintenance and care then most civilian aircraft. Also you may note that the Cessna 172 is a piston driven aircraft while the Learjet and the A-10 are both turbine engines, which are more costly and more complex to maintain. However the A-10 only makes allowances for the pilot, while both the Cessna and the Learjet allow for multiple passengers.
While it would be cool to own such a piece of military hardware. The operating costs make it prohibitive to fly with out a substantial bank account to support it.
Back to the 30mmx173
When the 30mmx173 was conceptualized the Cold War was in it’s height and the round was designed to be effective against Soviet Armor at that time. This included Soviet Tanks, Personnel carriers and support vehicles. The round has also proven effective as destroying all sorts of military hardware, including more fixed assets such as radar installation. The primary material used in Armor Piecing (AP) munitions at the time time was depleted uranium.
Depleted Uranium has several material characteristics that make it ideal for it’s use in AP ordinance. It’s high density, 1.67 times that of lead, imparts higher sectional density to the round which helps punch through armor. Perhaps the most interesting material property of DU is it’s ability to self sharpen as opposed to mushrooming or spalling as lead may do. When the penetrators hits the target the nose shears away in such a manner that it always presents a sharp tip. This keeps the energy of the round focused on a very small area which bores it’s way through all manner of armor plate.
Conversely DU is used in tank armor for the same reason it is used in AP rounds. It’s a fairly hard, dense material, it is often composited with steel and ceramics to create a fairly substantial obstacle to even modern tungsten core AP rounds.
The hardness of DU is about 47-49 on the Rockwell C Scale, comparatively this is softer then tools steels, but many, many times harder then lead. If the relative hardness and the self sharpening material property was not enough, DU is also flammable. Similar to magnesium it burns with a seriously hot flame becoming molten at around 2,200 (1,132 Celsius) degrees Fahrenheit and burning at over 10,000 degrees. Once a DU Penetrator pierces armor, the heat generated instantly ignites the remains of the penetrator creating what is likely akin to a arc flash explosion on the back side of the armor plate.
Depleted uranium is not as radioactive as uranium used in reactors, at about 60 percent of naturally occurring uranium as much of the 235 isotopes have be depleted and it is not a significant source of plutonium. However it would be incorrect to state that is does not pose some radioactive risk. There have been studies that have indicated that exposure to DU, both fired and unfired munitions, are not significant sources of radiation poisoning. That is not to say that ill effects could not be realized over prolonged exposure, but it is not as dangerous as some isotopes.
With that said, the military has largely gone away from using DU in munitions in favor of the more radiological inert tungsten. Tungsten has a slightly higher density then DU and is harder then DU. This makes it harder to work with, as tungsten is not easily machined. However it performed better on average in penetrating armor then DU, at the cost of it being relatively inert, it does not self ignite like a DU penetrator does. It also is not as controversial in it’s use as it does not leave any radioactive reside on the battlefield.
While the 30mmx173 was primarily designed and intended to pierce armor thus the focus on AP round design, it also has other loadings including tracers, incendiary, and explosive rounds. Since it’s introduction and use in the A-10, it has been adapted for use in ground support vehicles often referred to as light armor.
What practical use does it have for a civilian?
It would be limited, though, in my imagination I dream of one hell of a Extreme Long Range (ELR) gun, but honestly there would be significant design challenges in building even a single shot rifle around this cartridge.
For one, the impressive 3,500fps muzzle velocity is achieved through the use of a 8ft barrel. Yes, we could shorten the barrel some, but you still will have a long, unwieldly barrel.
The second major design challenge is how to deal with the recoil force produced by a 3700gr grain bullet and 2,000 grains of powder. The rifle wound need to be of sufficient mass to slow down the recoil impulse, no doubt a combination of muzzle break, spring buffer and a heavy gun can overcome this problem at the cost of mobility and practicality.
Surprisingly, sourcing powder for a cartridge like this is not difficult, the slower burning US 869 may be used, however lighting off a powder charge might be a bit trickery. I have also found sources for virgin cases, and bullets. The cases being the bigger concern as they represent the more difficult component manufacture.
Lastly, the legality of it all. As far I am aware, the ATF is not allowing the new construction/registration of destructive devices (which this would surely be considered due to bore diameter) which utilize modern ammunition. Modern ammunition being defined as ammunition utilizing a cartridges case. Historical pieces of military hardware, such as German 88’s are in private hands, and people do fire live ammunition out of them, but they are rare and expensive.
With that said, there other other examples of destructive devices that are not historical and have been granted some sort of allowance by the ATF for civilian ownership.
Other Examples of Civilian Made and Owned Cannonry
Before we get into this, let’s clear the smoke on something. The original intent of the 2nd Amendment was to allow civilians to own the exact same arms as the country they inhabited. So the fact we have to point out where the ATF has made allowances, is contrary to the ideal’s of a free nation.
For this we will focus on direct fire weapons. By direct fire, I mean firearms that you point at the target directly making small adjustments to the sight to compensate for wind, bullet drop, ect. The opposite of this is, indirect fire where the barrel it pointed up at the sky and the target is not directly aimed at, rather your aiming to achieve a certain ballistic trajectory to reach a target that cannot be view due to terrain obstruction or extended range. Mortars and Howitzers are both examples of indirect fire weapons.
Once the ranges are increase, even direct fire weapons start to look a bit more like indirect fire, you have a significant amount of arc in a direct fire weapon which quickly increases with range. Funny thing is, direct fire weapons used to be used as indirect fire weapons more often then we think, this is the origin of volley fire sights found on many older military weapons.
20mmx102 Anzio
Likely the most notable example of a direct fire rifle in current production and sold as a civilian rifle is the Anzio 20mm rifle. This rifle was designed and is being sold by the Anzio Ironworks Corporation. The rifle itself fires the 20x102mm Vulcan round, to convert that into Imperial units, it’s slinging a .787in projectile, or roughly a round the size of a 12 gauge shotgun bore. When I last checked the price of the 3 rounds mag fed rifle starts at merely $12,000.
They sell a single shot version, and even a mount that attaches to the fifth wheel in your truck. That’s innovation I enjoy. Anzio also has a wildcat round based on the 20x102mm which necks the case down to 50 caliber. This results in a 30% increase in velocity, and boosts muzzle energy to over 51,000ftlbs.
The report range of these rifles are 5000 yards or 2.6 miles. That is a long shot to be making. Most people would wonder where such a shot would be possible. When you are shooting at these ranges optics become a bit of a problem, as even high power optics make it hard to see the target.
Of note here, is that the ATF has not granted a sporting exemption to the 20mmx102 round. Which means purchase of a rifle requires NFA paperwork, which include finger prints and I believe a $10 tax stamp. This is obviously a bit more involved then filling out a 4473.
.950 JDJ
This interesting cartridge is based on the 20mmx110 Hispano case necked up to take a .950 caliber 3600gr bullet. I only address this as it has gained a bit of renown to date but it is a cartridge that falls in the realm of novelty. Only three of the rifles were ever made by SSK, and ammunition is no longer produced.
It would be interesting to know what SSK Industries (Now owned by Lehigh Defense) has intended for the cartridge. Novelty is a perfectly ligament excuse in my book, but given the time and investment, I would assume maybe they had something more instore but it was never realized due to the cost, or impracticality of the round.
One interesting point is that SSK Industries petitioned the ATF for a sporting exemption for this round. Unlike the 20mmx102 rifle chambered in this round are not considered destructive devices and can be transferred much like any other firearm.
So What’s Being Used to Set Records?
I mention the possibility of a 30mmx173 being the basis of an ELR rifle. After all, that’s what the Anzio rifle was predicated on. ELR with a touch of “Because we can”. However in assessing the legitimacy of using this for ELR, we should pause and take a look what the experts are using to set ELR records.
Its hard to envision what a 2 mile shot looks like. My longest shot with a hit was 1950 (1.1 Miles) yards achieved using a 338 Lapua, at the shooting range in Price, Utah. It took me 15 shots before getting dialed into get that hit, I missed on shot 16 and hit again on shot 17. In many parts of the country finding an open space to shoot this sort of distance is the first challenge. The western United States is full of such opportunities, due in part, to the vast swaths of publicly owned land.
It would make sense that the west was where Paul Phillips decided to achieve his world record shot in July 2020, where he hit a target at 4.0 miles with his rifle chamber in .416 Barrett. It was reportedly took his 13 man team 69 shots and the bullet’s apogee was 2,300 feet above bore line. The bullet took 22 seconds to arrive at the target. I could not find what the size of the target was but for reference if his team was shooting .5 MOA the group diameter at four miles would be 3,500 inches in diameter or about 300 feet.
The .416 Barret is an ELR cartridges’ designed by Barrett Manufacturing to exceed the long range performance of the 50 BMG. It is substantially smaller in diameter then 20mm (.416 verses .787) and the fact that someone such as Paul Phillips it using the .416 over 20-50 Anzio, 20mmx102 should tell you a lot. It may come down to the cost per round, as shooting ELR takes a lot of practice, and cost of the ammunition is a factor.
When shooting at these distances there are numerous challenges, beyond just selecting the right ammunition. For one, having optics that will allow you to see what you are aiming at and all you make enough of an adjustment, typically this means you have a rail that has a built in MOA adjustment. On my long range rifle I have 20 MOA built into the rifle rail, and 20 MOA built into the scope mount. I have no idea what the angle would need to be on a rifle designed to shoot 7,000 yards but it would not surprise me to see well over 100 MOA.
You have the normal variables in effect when you make any shot, these variables include drag, gravity, Coriolis effect, Magnus Effect, spin drift, and wind. At 7,000 yards I would imagine that the bullet would reach terminal velocity, meaning that it is dropping at a constant rate rather then an acceleratory rate. In other words the affects of gravity are balanced against aerodynamic drag in the Y-Axis. While you are still dealing with normal drag relative to velocity in the Z-Axis. The Coriolis Effect, and spin drifts are relative constants, and can be compensated for but drift due to wind, and the Magnus effect are variables which would be more pronounced the further the distance the target is an would be difficult to compensate for.
No of these problems are simply solved by moving to a larger caliber bullet, though a heavier bullet with a high cross sectional density may be less affected by some of these variables. I do not believe that math is made any easier due to the fact we can ignore any of these effects. In short, there are likely both practical and economic reasons to why moving to a medium caliber for ELR does not make sense.
Ammunition and Component Sources
It is one thing to own a Medium caliber firearm, it is another to feed it. After all Remington and Winchester do not seem to manufacture it. The best source of components is military surplus, and there seems to be only one source that sells it, that I have found. CVDS.com, a veteran owned and operated milsurp store. All of the projectiles are inert practice rounds, but they are the only place I have found that sells loaded ammunition, primed brass, electronic primers, and projectiles. They have a selection from 14mm all the way up to 57mm
I have to admit, as someone who enjoys ballistics, this site is becoming a favorite to add some unique mantle pieces for my man cave. At the very least, they make good conversation starters. 20mmx102 Vulcan is actually fairly reasonably priced at $35 per round. Expensive? Sure, but not as expensive as I thought it would be.
Sources for 30mmx173 are limited, and the loaded ammunition is a good deal pricier being close to $300 per round for target ammunition. Based on components that I have found I believe it can be loaded for roughly $80. About $20 per projectile, $7 for powder, $1 per primer, $50 per pre primed case. This assumes that you are able make or find custom made dies and press.
A Solution in Search of a Problem
Being the engineering mindset, I wonder if there is an industrial application for such a weapon. Given that the feasibility of using as an ELR platform is quite suspect due to ammunition cost alone, we cannot justify owning one for that reason alone. So what other uses might there be? This is where it could get interesting as it turns out there are practical applications for delivering kinetic energy to areas that are largely inaccessible.
Recoilless rifles which are often approaching or exceeding 100mm in caliber, are used to initiate control avalanches. This is one means of an industrial type application where a large amount of energy needs to be reliably and precisely delivered. We also see examples in the foundry, and industries with large cooling tools utilizing 8 Gauge shotgun shells firing 3oz slugs.
These slugs are used to break up plugs in the bottom of refractory furnaces, or to knock down large amounts of scale on the insides of cooling towers. Interestingly enough, the ATF grants rather large leeway’s to the application of these devices, including allowing for them to be suppressed, without registering through the NFA. These exemptions rely on the fact that the tools are large and generally considered “immobile”, or rather, someone is not going to walk off with one to use in their duck hunt blind.
So is there an industrial application for a 30mmx173 chambered cannon? Well, I believe there may be. Stick with me here as I have to draw on my observations from working in the mining industry. Most of my mining experience has come from hard rock open pit mining. We worked in fairly small pits, and were constantly on tight budgets. We sometimes ran into situations where we could see a potential rock fall, but had little in the way of doing anything about it. Sometimes we could have the blasters hang down a boost charge in front of the potential rock fall. The resulting blast would usually dislodge the rock in a safe manner.
The set up time, expense, and the regulation around the handling of explosives did not always make this a feasible option. Sometimes a condition would develop and we would have no choice but to work within the pit until it could be resolved. Coming from the firearms industry and knowing of the availability of 8 Gauge industrial applications I spent sometime investigating their possible use to initiate controlled knock down of problemed areas.
The concern was the amount of energy needed to dislodge some of these rock falls would be greater then what the 8 Gauge 3oz slug was capable of delivering. Unable to prove that this idea had merit on paper I was never able to get approval to trial such a device. There were concerns I had as well, given the relatively short range, and potentially mediocre accuracy of an 8 Gauge slug, a trial may have yielded unsatisfactory results. After all, we were relying in part on precision, being able to hit the potential rock fall in the area that would have the greatest odds of destabilizing the potential failure.
That is where I looked to something bigger, and something that would have a significant amount of energy, precision, and availability that we’d have the best chance of success. That’s where I think the 30mmx173 may fill that spot. A 3700gr projectile shot from a 60in barrel will leave at 3200fps and will have ~87,000ftlbs of energy at the muzzle.
My natural inclination would be to look at what is available and to set up a smaller scale trial rather then going to the larger more expensive caliber. For this the 20mmx102 would make a lot of sense. The investment would still be substantial, the rifle cost being at a minimum of $10k, and a per shot cost of somewhere around $40. However it is available, and it contains significant amounts of energy, enough to dislodge rock and destabilize marginally stabile fracture zones? Perhaps. It is hard to know for sure until it is tried.
Technical Specifications
Tracking down the cartridge dimensional specs has been a bit of a chore. I finally found a NATO standard to reference and was able to reference the standard when putting together a model. However there are something lacking, unlike many military standards the NATO standard for 30mmx173 does not line out the internal wall thickness of the case. This means I had to take a guess based on my experiance of drawing cartridge cases and the reported internal case volume of 173.30cc.
A few other notes on this drawing.
- Primer pocket dimensions were not immediately available. A 50BMG primer pocket was used for reference.
- Since the original design intent for this cartridge was to be used in an aircraft, the cases are typically made of aluminum rather the brass.
- Average pressure was reference from QuickLOAD, Individual Max Pressure was listed on the NATO STANAG document.
Wrapping It Up
Sometimes interesting cartridges are not always practical to own. However it is fun to do some research, look for applications, and crunch the numbers. It is pretty clear, that besides novelty, or the need of an anti-armor mounted cannon, this cartridge likely does not have a lot of practical use outside of what it was designed for. Mainly to be a bad ass, soviet tank and armor cracker mounted to the underside of a warbird.
Often times doing the research, reading technical papers, comparing numbers to other cartridges on the market, leads to learning about things like the longest shot. That’s what this has been for me. Would it be cool to build and own such as cannon if for the only fact that you have something no one else has? Yeah, I think it would be pretty darn cool. However outside of that, it’s hard to make the justification.
I hope this has been a fun, and informative writeup for you, and if there’s something you’d like to add. Let me know, I’d be happy to update the article and give you the credit.