mm vs. "pounds"

[Maastrictian]

My question relates to the British use of "x pounder" to describe their gun sizes. How does this relate to conventional mm? And what does the pound refer to? Does a six pounder fire a six lb shell? Thanks!

--Chris

[jgdpzr]

You got it right. The Brits referred to their guns by the weight of the projectile. IIRC, the bore size for the six pounder was somewhere in the vicinity of 57MM and the 17 pounder was a little over 76MM. Probably a little off on those estimates, but I think they're in the ballpark.

[sage]

Errr... I could be wrong, but I don't believe the "pounds" really had anything to do with the modern projectile. I think it dated back much further to the 1700's where a 9 pound cannon shot a 9 pound ball of iron.

Buuuuuuut... I could be wrong.

Sage

[Guest Michael emrys]

"Does a six pounder fire a six lb shell?"

Pretty close. The British system that you refer to was a continuation of what had been a universal system of gauging artillery tubes. When a gun was called an 18 pound cannon, for instance, what was meant was that a solid spherical iron shot that would fit the bore would weigh about 18lbs.

After the middle of the 19th. century, guns began relying more on explosive shells which were less dense, but were increasingly elongated for better ballistic performance, so the weight remained pretty much the same for a given bore size. I was somewhat surprised to discover that even solid antitank shots weighed in pretty close to their stated guage/weight, so perhaps some adjustments were made to the rating system along the line.

BTW, in case you are ever interested, there is a formula that will give you a pretty close approximation of the expected weight of any given caliber shell:

W=C^3/2 (weight equals C cubed over 2)

where W=weight in pounds and C=caliber in inches. Naturally if the caliber is given in metric units you will have to make the conversion in order for the formula to work.

I've used this formula many times and compared the results to the announced weight of shells and it matches pretty closely.

Michael

[Guest Germanboy]

<BLOCKQUOTE>quote:</font><HR>Originally posted by sage:

I think it dated back much further to the 1700's where a 9 pound cannon shot a 9 pound ball of iron.<HR></BLOCKQUOTE>

Seeing that they allegedly were still having a drill move to keep the horses from shying in the RA until a few years ago, this sounds quite plausible.

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Andreas

It is amazing what you can learn from a good book...

[Jeff Pattison]

The 17 pdr was standard on the first Centurions which were built before the end of the WWII, but never saw service. In the all literature I have, I see the 17 pdr is listed as an 83mm weapon. It also works out using that formula that was presented previously.

[Guest Babra]

2 pdr = 40mm

6 pdr = 57mm

17 pdr = 76.2mm

Weight is the weight of shot, not shell, rounded to the nearest pound.

[Mattias]

Jeff,

The 83mm weapon is the 20 pdr gun mounted on the Centurions after the war.

M.

[Jeff Pattison]

Yes, I see that now. Thanks.

[Supertanker]

I suppose I could research this, but I'm sure someone else around here already knows the answer. Weren't there two versions of the 17lb gun? Thinking way back to my Squad Leader days, there was the longer-shell version used in the Firefly, and then a short-shell version used in the Comet (classified by Avalon Hill as a 76LL and a 77L, respectively).

[Mattias]

Supertanker,

Right you are, as my old English teacher would have said

The "77mm" gun mounted on the Comet tank was actually just a shortened (less power, less recoil) 17 pounder, designed to limit the amount redesigning needed for that tank.

The designation "77mm" was given to avoid confusing it with the 17 ponder as they, naturally, had the same calibre, 76.2mm.

M.

[tss]

I think it dated back much further to the 1700's where a 9 pound cannon shot a 9 pound ball of iron.

Even further back. I think that the standardization of gun sizes started in early 16th Century (at least Charles V of Holy Roman Empire used fixed size guns).

- Tommi