As British tank guns are usually expressed in terms of pds, what is a pd?
For example, 2 pdr, 6 pdr, 12pdr, 17pdr. This has puzzled me for years so I am finally asking.
Pounds are the weight of the shells. Sixteen ounces to one pound.
I think the two-pounder was about the equivalent of the 35mm - I’m sure someone else will give you a detailed report.
2 pounder = 40mm
6 pounder = 57mm
12 pounder = 76.2mm
16 pounder = 76.2mm
25 pounder = 87.6mm
Thank you very much. I guess I could have found them myself. Now it is understood. 
It’s worth adding that some of the weights became very nominal, being fixed to the calibre. So all 57mm guns were known as 6 pdrs, even though they often fired 7 lb shells.
Note the two different abbreviations: “lb” is short for “pounds”; “pdr” (or “pr” - both were used) is short for “pounder”.
Another weight measurement you’ll come across is the weight of the gun, measured in hundredweights (cwt). 1 cwt = 112 lbs or 51 kg. So you get the “6 pdr 7 cwt gun”, which was the WW2 57mm anti-tank gun. The “6 pdr 8 cwt” was the WW1 naval and tank gun, the “6 pdr 10 cwt” the WW2 Twin Six coast defence gun and the “6 pdr 6 cwt” the experimental late-WW2 automatic AA gun. They all used different ammunition.
Presumably, then, the guns derive their names e.g Six-pounder from the weight of the rounds around which they were initially designed and that as ordnance technology improved weights became variable?
If so, would that require a certain balancing of warhead to charge, so as not to damage the weapon, and, thus, the duarbility of the weapon itself become the limiting factor in any further improvements in the ordnance - or have I got it toally wrong?
The guns kept the shell weights they were designed for. The 6 pdr 7 cwt fired a 7 lb shell from the start.
This did not happen with larger calibres: 76.2mm guns were variously known as 12 pdrs, 13 pdrs, 15 pdrs and 17 pdrs depending on the shell weight they were designed for.
7cwt what do you mean by 7cwt? Is that seven hunredwieght, i…e the wieght of the gun?
Would you know why it wasn’t named the 7pdr?
See post No.5
Would you know why it wasn’t named the 7pdr?
See post No.5 - it was called the 6 pdr because all British 57mm guns were called “6 pdrs”, regardless of their actual shell weight.
Thank you for that. I would presume that the first 57mm was a sixpounder, then, and that those that came after fell into tha category?
Otherwise, I don’t see any logic behind the 6pdr being the 6pdr.
Hello Tony
Do you have a picture pf the 6pdr 6cwt?
The only one I know of is in Ian Hogg’s “British & American Artillery of World War 2”.
Does anyone know of an online source for comparative anti-tank performance for the 2pdr and 3pdr guns? I’m assuming that the 3pdr was discarded in favour of the 2pdr for a reason, but when it comes to the military the reasons could have nothing at all to do with efficiency
The 3 prd was very poor, a 47 mm weapon with 620 m/s, the 2 pounder was a lot better.
According to the Royal Armoured Corps Tank Museum, the 3 pdr penetrated 25mm/1,000 yards/30 degrees, the 2 pdr 40mm.
Thanks for that, that’s about what I suspected.
Nice english revolvers from WW2
Enfields, yup, Very slow muzzle velocity, but heavy projectile, effective as a .45 acp.
How on earth have you worked that out ?
No chance.
