The British used to (still?) classify their guns by weight in pounds rather than caliber. Was that a constant across shell types?

Question

We just had a question about a 1 pdr (37mm). The 6 pdr is a 57mm and the 17 pdr in the Firefly was a 76mm.

So, far, so good. It's even not too difficult to follow the progression: it's roughly based on the cube of the diameter.

My question is however: is the weight of the projectile constant across shell types? I would expect an HE round with fragmentation capability to differ significantly from armor piercing round (and that's before we get into sabot rounds, which came much later). What did they use as a reference?

In addition, this is really a long standing tradition, going way back to naval guns of the 18-19th century which were solid round shots. This continuity makes me wonder if they even weighed modern shells, or were extrapolating from the calibers of older, round, solid shots.

I know, I know, it doesn't matter all that much. But it has always intrigued me in with regards to the use of this, odd-sounding, classification scheme.

p.s. Is it just the shot that's getting weighed? Or does it include the propellant and shellcase?

p.p.s. Yes, the British do seem to have done away with this approach, starting sometime around the introduction of the L7 105mm gun on the Centurion MBT, in 1958.

The Royal Ordnance L7, officially designated Gun, 105 mm, Tank, L7, is the basic model of the United Kingdom's most successful tank gun. It is a 105 mm L/52 rifled design by the Royal Ordnance Factories, intended for use in armoured fighting vehicles, replacing the older QF 20-pounder (84 mm) gun mounted on the British Centurion tank

Answer 1

Traditionally, in the age of sail, it used to be just the solid shot.

Later on, this was a nominal designation roughly correlating with one of the projectiles designed for the weapon. The 17-pounder fired 17-lb. "kinetic energy" anti-tank rounds, and the 6-pounder fired 6-lb. KE rounds, in both examples without propellant. The 2-pounder, meanwhile, fired 2.4-lb. KE rounds.

Answer 2

Is the weight of the projectile constant across shell types?

No, of course not. Take for example the Ordnance QF 6-pounder. Its shells varied from as little as 1.42kg (3 lb 2 oz) for APDS to 3.23kg (7 lb 2 oz) for APCBC. The US fired an even heavier APCBC/HE round, at 3.3kg (7 lb 4 oz). On the other side of the channel, the German 8.8cm (anti-) tank guns of WWII ranged from 7.3kg (APCR) to 10.4kg (APCBC/HE). In either case, there's a number of shells with intermediate weights as well.

The use of "...-pounder" stems back from the Age of Sail, where you would have e.g. a number of 6-pounder, 12-pounder, 24-pounder, and 32-pounder guns to a broadside, depending on ship type. Most of the time these cannons fired solid shot (with chain or grape shot being available options), which was carried to the guns by hand. This made the weight of the shot an important issue.

Answer 3

the warthunder guys did that research. With a quick search on their forums I found a reference with weights for different ammo types: https://forum.warthunder.com/t/british-sub-caliber-ammunition/2822/16

They have a wiki page for their game where ammo types for each vehicle are listed. It may be not always right, but it will give you a basic quick assessment, at least:

https://wiki.warthunder.com/unit/uk_a_34_comet_iron_duke

Cannon QQF mk II: APDS 2.5kg ~ 5.5 pounds ; APBCCS 7.7 ~16.9 pounds ; HE 7kg ~ 15.4pounds

https://wiki.warthunder.com/unit/uk_17_pdr_m10_achilles

Canonon QF-17 : no APDS; 8.4kg (18.5pounds) smoke shell and APBC as above.

you may check their assessment of ammo types and weights for a wide variety of british vehicles: https://wiki.warthunder.com/ground?v=t&t_c=britain

take care: previously, they researched penetration values for each cannon/ammo which were taken from tables such as given above. Today, penetration values in the game are calculated by a universal formula.

Also, interestingly, the reason that they gave up on 'real' penetration values was that it was too hard to be sure about them. There are too many variations on models of cannons, vehicles, ammo, etc, and way too much variation on penetration experiments and ambiguities in their historical documents. It became too time consuming for them to judge the validity of each reference. So, take everything with a grain of salt, if you want exact numbers.

PS: it looks like some pp get really passionate about historical research when their preferred game appears 'wrong'

Answer 4

The "poundage" caliber is the nominal weight of a round iron cannonball that could be fired from the gun. So, an iron cannonball for a 37mm muzzle-loaded smoothbore would weigh about a pound; for a 76mm one, 17 pounds. Rifled guns carried over this designation even though they were never used to fire roundshot.