Terminology Help - Driving Band vs. Obturation Band


#1

I am hoping that I can get some help on the correct use of some ammunition terminology. I am curious if there is a difference in meaning between “Driving Band” and “Obturation Band” when referring to projectiles? Is the terminology interchangeable?

Jason


#2

Actually these are two very different things.

A projectile for a smooth bore gun can/shall have an obturating band and as a matter of course no driving band as such is not required.

While a driving band basically is an obturator as such and depending on design (more often seen with older designs) a driving band may have a special obturating section which is usually very fine and somewhat larger in diameter than the rest of the driving band.

Also means that an obturator is doing exactly what it says; it is sealing something. Not more and not less. Also obturators are usually less strong in design (see plastic material being used nowadays or if made of metal are just fine over diameter flanges attached to a projectile) as these do not take or transmit any force (unlike a driving band).

After all driving bands do transmit rotation taking it from the rifling of a barrel and relaying it to the projectile.

Edit/addon:
A good example are obturating bands on APFSDS and HEAT projectiles which are fired from rifled barrels. There they are made of plastic as just sealing is required and no spin forces are to be transmitted. As you know these are then not even fixed to the projectile and do rotate free on the projectile bodies so they do not even transmit the slightest spin to the projectiles as it is not wanted (in particular with HEAT projectiles).


#3

Thanks big time, Alex! Your explaination above is super helpful. The part about the smoothbore guns is particularly helpful. I am working on an IAA piece on 120MM APFSDS ammunition and had some terminology confusion. Really appreciate your help.

Jason


#4

It might also be worth mentioning that driving bands are often called rotating bands in the US (which is a rather more logical term).

Alex, I don’t think that the free-rotating obturating bands for APFSDS fired from rifled barrels completely prevent projectile rotation. I recall reading long ago that on the British 120mm, friction between the obturating band and the projectile results in the projectile spinning at about 1,200 rpm (IIRC) as it leaves the muzzle. This is not enough to destabilise the projectile, and it is considered useful in assisting clean sabot separation as the rotation throws the sabot pieces clear.


#5

Tony, you are right, some spin rate is transmitted but I did not make a point of it as it is not the full rate and merely an unintended friction transmission of the freee obturating band. I should have been clearer about that. This raises the question now if there were designs which had a fixed obturating band which actually worked like a driving band? Or did you refer to exactly this?
Concerning the spin of APFSDS penetrators/arrows we see that spin is also generated by angled front edges of the fins on some of these - for the reason you mentioned; to create some low spin rate.

Jason, maybe you can look up your specimens and see if you find types, models and countries which started to use the angled front edges as I recall having seen some without this feature.

BTW: the Russian used free spinning obturators on HEAT projectiles (folding fin designs) which were basically made like regular driving bands and were sitting on a loose steel ring. This ring transmitted still some sping (due to friction) which ingeniously was later compensated by the folding fins which had small latches which bent on firing and acted exactly against the spin which unintendedly was generated by the obturator (as said above).


#6

Not simply “often called”, but more correctly “always called”. At least they were in my Gunners Mate days. I know that naval ordnance has changed considerably since those long-ago times but, from memory, the rotating band had three primary functions. 1) To seal the bore. 2) To position and center the rear of the projectile. 3) To rotate the projectile.

FWIW

Ray


#7

Thank you all so much for your help explaining this. Super helpful!

Alex, most of my collection is at my parents house as I am in the process of building a new house. At this time, I only have 120MM inert APFSDS specimens in my office from the US and Germany. So far, all of them have beveled angles on one side of each leading fin edge.

One more terminology question, some of the sabot assemblies have a 2nd band, usually a lot thinner, on the top of the sabot. Would this also be called a obturating band?

Jason


#8

Jason, the second band on top at the bourrelet is a “centering band”. Often observed on older ammunition designs (partially into WWI and with exceptions also later) these were used to reduce barrel wear. Basically these bands are nothing but a soft protection material which prevents the steel/metal body of the projectile from making contact with the bore.
These bands sometimes do slightly engage with the rifling but often have the bore diameter. Means they are not obturating and they are also no driving/rotating bands.

On APFSDS designs these are also often the upper connector of the sabots where they add to a better fixation of the projectile before firing. Means here this band is having two functions.


#9

Let me summarize everything in “my language” to see if I got it right. Driving band = a band which squeezes into rifling and thus makes a projectile rotate. Obturation band = a usually softer material sealing band the main purpose of which is not to allow gases to go forward, not to bypass a projectile. Would a sabot be an obturation device?


#10

Particularly with the large caliber projectiles, it was common practice to provide 2 bourrelets, one just below the ogive and another in front of the rotating band. These bourrelets were ground to a fine finish and were held to strict dimensions. Prior to WWII, the bourrelets were not painted but in later years one thin coat of body paint was permitted.

Bourrelets served only to center the projectile in the bore.

Ray


#11

Thank you everyone.

This information is a really big help. I am happy I asked for clarification before I submitted anything for printing as I was using the completely wrong name in my descriptions. Whew, close one. :-)

Final Question: Is, “Obturation Band” ok to use grammatically sometimes in a sentence, or is it always, “Obturating Band?” My spell check hates them both :-) Again, thank you all for your help.

Jason


#12

US technical manuals and here in particular the
TM 43-0001-28, Artillery Ammunition Data Sheets, 1994
says:

  • Obturator (on: 90mm HEAT-T, 105mm APDS-T, 105mm APFSDS-T, 105mm HEAT-T, 120mm HEAT-T, 155mm)
  • Obturator ring (on mortar projectiles)

#13

Vlad, all correct.
A sabot is not intended as such to be an obturator but depending on design and caliber it may also serve the purpose of an obturator (like a driving band is also obturating).
Here you would need to clarify what sabot/projectile you have in mind.