AIUI, swabbing after each shot serves two purposes: It gets rid of accumulated soot from a shot, and it also cools down the barrel in case there is any flaming debris, which could ignite a subsequent shell put into the chamber.
But for some cannons, such as the 105mm howitzer aboard an AC-130 gunship, I have seen footage in which the crews just load shell after shell into the cannon and fire them successively without any swabbing in between. Do some cannons not need swabbing?
I believe that pretty much only black , or muzzle loading cannon, require swabbing between rounds. In those cases loose powder, or powder contained in a flammable cloth bag is passed down the bore. This could be ignited by embers from the previous shot.
In most modern cannon, the complete projectile, propellant, and ignition unit are contained in a sealed metal container. No chance of accidental ignition. Large bore naval guns are , in some cases at least, still use bagged propellant.
155 mm howitzers as well. I don’t think they swab the barrel, though I imagine they clean it between fire missions.
It’ll take an ordnance specialist to answer for sure, but I suspect that the ones that need swabbing are the ones in which the shot and propellant are loaded separately, putting the propellant in direct contact with the barrel. This would include old-timey cannons, as well as the big 16-inch guns used on battleships in the latter half of the 20th century.
Other artillery devices, such as the howitzer on an AC-130, take self-contained cartridges. As in a handheld gun, these cartridges include a casing on the back end of the projectile that holds the propellant. In this situation, the propellant never contacts the barrel directly, and so one would expect more resistance to spontaneous/uncommanded firing - providing at least enough time to get the breech closed.
In 1989 the USS Iowa battleship had a 16-inch gun that exploded, killing 47 sailors. The gun was being loaded, and the propellant ignited before they could get the breech closed. Investigation concluded the cause was likely a malfunction of the automatic ram that pushed everything forward into the barrel, with frictional heating lighting the propellant. It’s entirely possible that a poorly-swabbed barrel, leaving hot spots, may have also been a factor.
I see. I have seen land-based howitzers, though, such as the M777, that needed swabbing after every shot, although that was probably because the crew was loading in “cheese charges” - the separate, range-boosting yellow or green packages after the shell itself was loaded. I am guessing that if they were shooting shell alone, with no cheese charges, that they wouldn’t have to swab?
I have also heard that even with entirely self-contained shells, they can still cook off and explode if the barrel is too hot, which is what one AC-130 risked doing during a November 2016 battle in Afghanistan in which the friendlies on the ground were in such dire circumstances that the gunship had no choice but to keep firing shell after shell to keep the enemy at bay even though it risked premature detonation and destruction of the airplane.
Firing procedure for the 16 inch gun doesn’t have swabbing, but compressed air is used to blow any remaining powder residue out of the barrel and chamber.
I can’t tell from watching 155 crews do their thing. Maybe a guy swabs or inspects the breech before another shell is loaded?
105s, like on the AC-130, use semi-fixed ammunition. (Which is not the same as fixed ammunition, like a small arms cartridge, though I’m not understanding the difference.) Weirdly, despite being bigger than a 155 howitzer, so did the 8 inch guns on ships like the Newport News.
As I understand it, there’s a shell, and a cartridge casing, but they’re not together, like a small arms cartridge, or tank shell, or whatever. The idea is that cased rounds can use a simpler breech block and whatever, as the case does the job of sealing the chamber, and the breech block just keeps the back of the gun together. Bagged charges require the breech block to do both- seal the chamber AND keep it all together. That’s why tanks and the like usually have simple sliding breechblocks, while bagged guns have more complex things like the interrupted thread breech blocks.
Semi-fixed ammunition does not have the projectile solidly seated in the neck of the casing. The design makes it easy to remove the projectile by hand, adjust the propellant in the casing, and then reseat the projectile before loading. It is a pretty common feature for modern artillery rounds.
I assume it is carried over mostly because they mounted an already designed towed artillery piece that used semi-fixed ammunition. Adjusting the charge doesn’t seem like it would be useful in a direct fire role from an aircraft.
The 155mm M-198 howitzer used separate charge, primer, and projectile. It was not swabbed after each firing, or even after many firings in a fire mission. It was (is) a breech loaded weapon.
I think it’s the older muzzle loaded artillery that needed to be swabbed, so that the powder for the next round did not ignite prematurely. That would suck for the guy ramming that next round in.
I was FDC for the M-198. I spent a little time on the gun line, but not a lot. So the breech loading thing is my guess as to the reason. That, and muzzle lengths were much shorter than they can be today.
This. You needed to swab out a muzzle loading cannon because if you didn’t you could still have some powder burning in the barrel when you tried to ram the next charge down which would be, um, sub-optimal. You also had bore fouling in the black powder days which was another reason to sponge out the guns, but mainly it was to ensure that there wasn’t any fire in the barrel when you were reloading.
Thanks! Ignorance fought. I saw the pictures of both types and couldn’t figure out the difference. Being able to adjust the charge would be really useful in indirect fire.
I can confirm that for example the M109 155mm cannon doesn’t need swabbing after each shot.
The loader checks the barrel visually after each shot to confirm that there is no obstruction in the barrel but that’s it. Since the round gets loaded first and effectively seals the barrel, the risk of unburned propellant igniting the next charge is very low. Modern propellant also leaves almost no residue compared to black powder charges, so fouling is not as big of an issue.
The barrels do get cleaned regularly, but that’s a maintenance task happening after shooting has completed and takes quite a while to do since you need to assemble the cleaning rod from 2 or 3 separate pieces and then run it through the barrel. Depending on crew motivation this can take 5-10 minutes to do (excl. assembly and disassembly) so it would be highly impractical during shooting (target time was 3 rounds in the first 15 seconds and 6 rounds in total in a minute).
I was told that one of the main reasons silk propellant bags were used for naval guns was that the material burned almost completely. WRT the Iowa turret explosion, I believe it was finally determined that the most likely cause was that old, unstable propellant was ignited when the bags were overrammed due to operator error.
The 105mm rounds are considered semi-fixed and easily separated to adjust the number of propellant bags. Depending on the type of round, they may come fuzed or with a closing plug. The primer is in the cartridge case.
The Naval rifles like the 8"/55 and the current 5"/54 fired/fire “separated” ammunition. The projectile/fuze combination is loaded/rammed then the propelling charge which is a metal casing (brass/aluminum/steel) with a primer in the base and a plug in the mouth of the casing. The propelling charge is non-adjustable. The loader could select full charge/full flashless charge/reduced charge / flashless reduced charge for the 8"/55 naval rifle.
They can and do swab out the 155mm howitzers between multiple shots. Surprisingly, it can be a long time between shots in a fire support mission. A call comes in for support; gps coordinates are checked, winds aloft if available, differences in altitude between gun and target plugged in, air temperature and pressure, you need air clearance (no helicopters/drones/ground support aircraft). Appropriate fuze is selected (PD, Time [electric/mechanical], proximity, etc,), settings double checked, projectile is placed in tray then rammed, correct number/type of propelling charges are put in chamber, breech locked, primer placed, gun aligned for azimuth and elevation, everything double checked again, lanyard pull, boom. Then you wait, two/three/four minutes to get back a report on where the shell landed. It’s traveling up to 45 km with a rocket assisted shell. Even longer with a gps/inertial shell that can do some maneuvers.
Then repeat with corrections. The same gun may be supporting multiple units in different areas at the same time. Actually lots more detail, it’s way beyond, “the whites of their eyes” stuff.