the cromwell's 75mm

[roqf77]

aince getting the concept of the barrel length wrong(flaming knives was right about that), i have been looking over the internet and after much looking i found a spanish site i think. it says the 75mm on the cromwell was a 17 pounder conversion with a cut barrel and it was a ultra velocity. im sure thats supposed to be high velocity .

http://www.europa1939.com/tanques/tanques/comet.htm

thats the link translate it in bablefish or something.

members.tripod.com/~chrisshillito/a39/a39txt.htm

this is a page on the toirtoise but does have info on the 75mm, it was a similar idea but a further down scalement of the 77mm on the comet.

the 75mm did use us 75mm ammo but it seems it isnt the same gun as the na 75mm type gun was not put in the cromwell, still not entirely conlusive but im still looking.

i have contacted the reme muesum and vickers about the gun nd am waiting further replies.

[John D Salt]

Originally posted by roqf77:

aince getting the concept of the barrel length wrong(flaming knives was right about that), i have been looking over the internet and after much looking i found a spanish site i think. it says the 75mm on the cromwell was a 17 pounder conversion with a cut barrel and it was a ultra velocity. im sure thats supposed to be high velocity .

http://www.europa1939.com/tanques/tanques/comet.htm

thats the link translate it in bablefish or something.

Even in Spanish, "Comet" does not equal "Cromwell".

All the best,

John.

[roqf77]

yes but if you actualy read the two pages carefully you would of noticed it states that the 77m in the comet was developed after the high velocity 75mm which was designe for the cromwell. thats why i said translate it unless you can read spanish or whatever language its in in which case you just didnt read both pages.

[flamingknives]

Would that be the high velocity 75mm that was developed by Vickers but never introduced? (Beale again)

The cut down 17pr. would be the 77mm, fitted to the Comet. In reality, both 77mm and 17pr. had a calibre of 3", 76.2mm.

[roqf77]

thats what im trying to find out, becuase the 75mm there refering does seem to have been fitted. hopefully should get some info from the reme or alvis-vickers.

[roqf77]

plus another manufacturer develeped a 75mm high velocity gun that was a shortened 17 pdr and produced a 77m for the comet i think, but vickers was chosen.

[flamingknives]

Strewth.

...becuase the 75mm there refering does seem to have been fitted...

Who are they? Fitted to what? When? Sources man!

A 75mm medium velocity (m.v.) gun based on the 6pr. was fitted to the Churchill, Cromwell and Valentine. This gun length is given as 36.5 calibres

A shortened 17pr. cannot be easily changed to a 75mm weapon, as the original weapon has a 3" (76.2mm) calibre. While this could be lined down to 75mm, why would you want to? The 77mm is a truncated 17pr. The different nomenclature was used to avoid confusion

HOWEVER:

There is some confusion inherent in Beale's writing in "Death by Design" He describes the 77mm gun as a high velocity (h.v.) 75mm gun, with a 50 calibre barrel. A table in the same book notes said weapon as firing a 15lb shell, the same as the US 75mm round that was also fired from the British 75mm medium velocity (m.v.) gun, though that gives the calibre as 76.2mm, as per the 17pr.. He does note that the 75mm h.v. gun would not fit into a Cromwell turret, and had to be fitted to a purpose built tank, the Comet. Every other source I've read describes the 77mm as a truncated 17pr.

Regardless of it's actual calibre, the 77mm was never fitted to a Cromwell, just something that looks like a Cromwell.

Oh, and technically it isn't even Alvis-Vickers anymore. That company was taken over by BAESystems, and is now part of BAESystems Land Systems. You'd be better off going through Governemental records, such as the National Archive at Kew or Bovington tank museum.

[Edit for backfiring comedy section]

[John D Salt]

Originally posted by flamingknives:

Would that be the high velocity 75mm that was developed by Vickers but never introduced? (Beale again)

I think you're misreading Beale. HV 75 was merely an earlier name for what was later known as the 77mm. It is not a separate weapon.

This is also what the Spanish site says:

"Vickers-Armstrong desarrollo una version compacta del cañon de 17lbs con un barril mas corto, una recamara menor y menor peso, dando como resultado el cañon Vickers HV* 75mm, denominado mas tarde cañon de 77mm"

Never having had a single Spanish lesson in my life, I translate this as:

"Vickers-Armstrongs developed a compact version of the 17-pdr gun with a shorter barrel, a smaller (size?) and lighter, resulting in the Vickers HV 75mm gun, later called the 77mm."

Originally posted by flamingknives:

The cut down 17pr. would be the 77mm, fitted to the Comet. In reality, both 77mm and 17pr. had a calibre of 3", 76.2mm.

I don't know what the true calibres of any of these weapons were, but I doubt they were any different. A three-finger gun's a three-finger gun.

Recall that the condemning limit of wear on the 17-pdr was one-tenth of an inch (2.5mm), so I think a difference of 1.2mm can be made up by the driving band any day of the week.

All the best,

John.

[flamingknives]

Hmm.

To quote the opening sentence on the 77mm, p108:

"This gun was in reality a long-barrelled 75mm, but was called the 77mm to differentiate it both from the 75mm medium-velocity gun and the seventeen-pounder."

He goes on to describe the 77mm as a 50 calibre gun, having a length of 3.75. Were it a 3" gun, 50 calibres would equal 3.81m.

Granted, the measurement of gun length can vary (from where to where, for example), but then why bother quoting a length to 5cm and then be more than 5cm out? The length of the 75mm m.v. is rounded to the nearest 5mm

There is a lot of variance or errors in that book, I note, as I cross-reference things, as p108 gives an MV of 2750f/s for the 77mm, and the table on p100 quotes 2575f/s. The same table also quotes a 15lb projectile weight for the APCBC round fired by the 77mm. A shorter table on p83 gives a projectile weight of 17lb and MV of 2750f/s.

p98 notes that Sept. '43 saw a decision to alter the calibre of the 75mm h.v. to accept 17pr. ammunition.

[John D Salt]

Originally posted by flamingknives:

[snips]

To quote the opening sentence on the 77mm, p108:

"This gun was in reality a long-barrelled 75mm, but was called the 77mm to differentiate it both from the 75mm medium-velocity gun and the seventeen-pounder."

Right. And we know from the paragraph heading that this is the 77mm, which fires the same projectiles as the 17-pdr.

Originally posted by flamingknives:

He goes on to describe the 77mm as a 50 calibre gun, having a length of 3.75. Were it a 3" gun, 50 calibres would equal 3.81m.

Granted, the measurement of gun length can vary (from where to where, for example), but then why bother quoting a length to 5cm and then be more than 5cm out? The length of the 75mm m.v. is rounded to the nearest 5mm

Spurious precision. I'm quite used to calibre lengths being vague to within a calibre or two. The T-34's 76mm I have seen described as L41 or L42, and the US 75mm M3 is designated an L40 by most people but CM:AK calls it an L38. The 75mm M2 is according to Hunnicutt 31.1 calibres from muzzle to rear face of breech, but everyone calls it an L30.

Chamberlain & Ellis, the armour profile on Cromwell and Comet, the Bovington booklet on British tanks 1939-45 and the Spanish site just quoted all seem to think that the 77mm (otherwise known as the 75 HV) was an adaptation of the 17-pdr. The 8-pdr (which Beale says was also 75mm calibre) might be a further confusing factor, but I would be very surprised if any version of the 77mm ever had any true calibre different from its final one.

You'll be telling me next that .357 bullets are narrower than .38s.

All the best,

John.

[The_Enigma]

i have to ask but what does truncated mean?

[roqf77]

fair points but all im saying is a cromwell tank crew said it was better v tanks than the sherman he was on previously. but to confuse things further i found out that american 75mm ammo had a high exsplosive head the british rounds removed this i guess made it back up to a apcbc shell. the us 57mm and the british 6 pounder had the same difference.www1.freeweb.hu/gva/index.html

according to cmak the us 57mm had noticbly worse than the uk 6 pounder due to the round if cmak vigures are accurate. however that would be the same as the sherman he was in before. my head hurts.......

[roqf77]

Angle 100m 500m 1000m 2000m

0º 118 106 92 73 APCBC (lg)

30º 91 82 71 58

us figures

[roqf77]

0º 123 110 95 75 APCBC shot

30º 94 84 74 59

uk figures on the l43 6 pounder

[roqf77]

0º 131 117 101 80 APCBC

30º 100 90 78 63

uk figures for the l50 6 pounder

plus uk penetration results recor the thickness of armour penetrated the us figures record from where a significant proportion of the shell penetrates to so although on the same gun it makes no difference in penetration the us figures would show a slightly higher penetration.

[flamingknives]

Truncated = shortened.

True, the British used AP shot, whereas the US forces had a preference for AP Shell, and shot will perform better against armour, inf not in behind armour effect.

That said, an improvement in ammunition would improve both guns. Perhaps the people you've been talking to used a Sherman with the old ammunition and switched to improved ammo when they switched tanks, and therefore guns.

[roqf77]

quite possibly i was at no point bringin into question your knowledge. you know more than me about equipment. it is entirely possible that is true, shame i just cant find any figures for it. anyway sorry fr the argument i also something about more propellant used but this could been done along with the he head being removed... my head still hurts

[flamingknives]

Originally posted by roqf77:

quite possibly i was at no point bringin into question your knowledge...

No, that's John's job.