Not too long ago Ukraine asked of its western allies to provide it with longer-ranged artillery ammunition. This brought many to the understanding that Ukraine wanted more shells like Vulcano and Excalibur, while in reality the majority of western-provided 155mm ammunition falls well short of the ranges that Wikipedia claims modern 155mm systems have.

To understand this phenomenon, we need to explore several niche and often misunderstood aspects of modern artillery, beginning with the barrel length.

Barrel length

First off, I will need to explain how the length of an artillery barrel is expressed. When looking at artillery systems, you will often come across this length being expressed in calibres. This is the number of times the calibre of the shell the gun fires fits into the length of the barrel. A 39-calibre barrel on a 155mm system will be 39 times 155mm long, or 6,045 metres in length (19.8 feet in not-so-freedom units). From this point onwards barrel lengths will thus be referenced to as L/39 for 39-calibre.

At a cursory glance, the longer the barrel is, the further it will shoot. While this is true in most cases, there are some exceptions. Shells that had been designed to operate with shorter barrels, like the US M107 shells, are often only able to be paired with propellant charges optimised for those older and often shorter guns that operated under lower pressure.

This leads to there not being enough powder in the charge to fully eject the shells from the barrel. This causes the shell to start losing velocity before it has even left the barrel and thus reduces the shell’s range. The M107 previously mentioned is a great example of this happening, as it loses roughly 200 metres on its maximum range when fired from an L/52 barrel compared to when it is fired from an L/39 barrel.

Chamber size

Other than barrel length, one also has to consider the internal volume of the barrel’s chamber, as this determines the amount of propellant that can be loaded.

Here again it is not as simple as “bigger number better”, as larger-sized chambers will also reduce the range of the shell if not enough propellant is loaded into it, as the leftover space results in a greater volume needing to be filled with hot gases before they start to push the shell out of the barrel.

Shell shapes

• Boat Tail: BT shells have an angled section at the base of the shells that is meant to reduce the size of the negative pressure zone behind the shell, thus reducing the drag that the shell experiences and increasing its effective range. This effect can be enhanced by leaving the Boat Tail section itself hollow.

• ERFB: Extended Range Full Bore, while not having a real definition, generally refers to artillery shells with a more aerodynamic body shape inspired by or copied from the shells introduced by Denel in the mid-1970’s.

Shell boosters

• Base Bleed: Also referred to as Base Burn or BB, is a gas generator mounted on the bottom of an artillery shell which expels gas into the low-pressure zone behind the shell during its flight, creating a “perfect” Boat Tail. This reduces drag and results in the shell having both a longer range and similar or slightly worse accuracy depending on the shell in question.

Base Bleed units are most commonly found on boat tail shells, where they can screw into the hollow base of the shell body.

Rocket Assisted Propulsion: Also known as RAP. These shells come with a rocket motor that powers the shell’s flight after the projectile leaves the barrel. This extends the range of the projectile but comes at the cost of both the internal volume of the shells, as a lot of it is used to house the rocket propellant, and a reduction in the accuracy of the shell.

If you want to look more into artillery ammunition ranges and fillers, then feel free to take a look at the database that I and @Helvegen29 (who also assisted in writing this article) have been working on.