A Better 6 pounder

[Shortround6]

The won't fit problem is due in part to mistakes made in 1938-1940 in tank-design and procurement. The Covenanter was a step backward and the Crusader was left playing catch up and barely got them back to where they were in 1938 (and that is being charitable) only with thicker armor. And so on.

Back to the question. How much improvement are you looking for?

Mr. Williams has two photos on his web site of interest to use here. the page is ANTI

the 4th photo down GERMAN BRITISH WW2 TANK GUN AMMUNITION and the 14th photo MODERN SUB-CALIBRE AMMUNITION (2)

The second shows the WW II 6pdr case next to the modern 60x410R (IMI / OTO 60mm) case.

As a rough rule of thumb a 10% increase in velocity needs 20% more powder.

Two guns used different length barrels with the same ammunition is this velocity range. the 6pdr of course with lengths of 43 and 50 calibers ( be sure your source is comparing the same ammo) and the German 75mm/L43 and L48 tank guns. the difference in armor penetration between the barrel lengths percentage wise is in the low single digits, further lengthening of the barrels would bring diminishing returns, an additional 5-7 caliber in crease in length would yield a smaller increase in penetration.

for "improving" the 6pdr (without changing the ammo type, like going to APCR or APDS) is going to require a bigger cartridge case. Can the existing barrel/chamber be bored out bigger or not? Can the existing Breechblock take the larger case (both in physical size and in strain) ? can the recoil mechanism handle the increased load or will it need to be modified?
Too many modifications and you are working on a new gun and if you are working on a new gun you might as well work on a bigger one.

 

[tomo pauk]

Think SR6 provided the implications about the extracting more penetration from the 6pdr.

I'll make an assesment about the needs capabilities of the W. Allied anti-tank 'machinery'.
In tracked form, they had the Sherman Firefly, Challenger, Avenger, Achiles, M4 (76), M-10/Wolverine, M-18, - all available for fighting in NE Europe in second half of 1944*. In towed 'flavour', there were 17pdr and 3in ATG. I've listed the 'tools' that were, more or less, able to penetrate Panther and heavier stuff. Sure enough, the Tiger II and Jagtiger would be somewhat safer than the lighter AFVs, but it looks to me that Germans were the ones that should be worried, not Allied tankers.
What the W. Allies in that time frame were short of was the AFV that would shrug off at least the 7,5cm L48 hits with ease.

One can wonder why the APDS projectile of the 17pdr was no adopted for the US 76mm, the performance would be as good as of 77mm HV (=165mm at 1000yds @ 30deg), and the modifications required far easier to pull off (changing the sight, instead of changing the main weapon; benefits: non-British/CW tankers can use it, too; the ammo count remains the same).
Sure enough, a JagdChurchill** (with 17pdr), or the JagdCromwell (at least 77mm HV, or US 76mm, or, hopefully, the 17pdr) sound great to me, once the fighting is out of the bocage country.


*with Comet arriving in late 1944
** a primitive version of that was produced in 1941, variant of the 3in AA gun being the weapon

 

[Shortround6]

The British did try something called the 8pdr which was supposed to fit into the 6pdr mounts and give a 28% increase in penetration using a 59 caliber length barrel using a 59mm bore (?). When the gun wouldn't balance in the mountings a shorter 48 caliber barrel was tried but performance fell off to little better than the 6pr, project canceled in Jan 1943.

 

[tomo pauk]

Somewhat related to the topic, a penetration calculator. Take it for what is worth:

WWII Gun vrs Armour Calculator

 

[yulzari]

You can make changes to the propellant within the same case but there are consequences.

A slightly longer burning propellant to keep the 'push' going up a longer barrel will raise breech pressure but British breech pressures were already higher than German ones.

Reducing the depth of seating frees up a little more case capacity but there are consequences there too.

The projectile can be worked on. A more accurate APDS would be a prime choice.

Can the recoil mechanism accommodate the extra performance or will it need upgrading?

Certainly it would be a further mark of the 6 pounder but no great changes and will still fit.I would expect it to be a whole package of minor changes rather than one magic one. More is always better but a 20% improvement over penetration found in 1943 will tip the balance I would judge.

The key thing is it must fit existing turrets to the extent that it is a simple swap. that is the only reason for pursuing this goal.

 

[Vincenzo]

First lets a fact or two straight. The 17pdr did not weigh twice what a Pak 40 did, it weighed about 50% more. It also weighed a whole lot less than than all the rest of the heavy AT guns the Germans dragged onto the battle field, like all those 88mm guns. Like the 75mm/L70 the 17pdr could out penetrate the 88mm/L56 at most normal combat ranges. .

i'm with dave for weight of 17 pdr, around 6400 lbs, 1800 lbs the gun and 4600 lbs the carriage. this is much less of 88 Flak 18/36 but this is for AA carriage of this. less but not so much comparating to pak 43. On paper has good advantage of penetration with same ammo v/s the flak 18/36 thanks to higher MV.

 

[tomo pauk]

From the UK AT guns book, Osprey New Vanguard, about the 17pdr:

Weight of gun and carriage: 2 tons 17cwt 1qr 251b or 6,5371b

It was really asking for SP version, from the Straussler conversion further.

 

[Shortround6]

There are a number of sources that give a weight of 4600-4700lbs "in action".

There may be a different definition for " weight of equipment".

A few books may have misprints or typos.

The Americans managed to build a few 90mm guns on a two wheel carriage at the end of the war, the T8 gun on the T5E2 carriage ( twice lightened from the T5) for 6800lbs with a 2290lb gun and breech.

The standard US 3 in AT gun went about 4870lbs with it's WW I style barrel and cobbled together 105 howitzer carriage.

But we all know the British couldn't possibly design and build weapons to rival the Germans

 

[tomo pauk]

The 'Anti tank weapons' by Chamberlain Gander gives 2,9 tons as 'in action' weight of the 17pdr.

But we all know the British couldn't possibly design and build weapons to rival the Germans

Under 160mm, Russian hardware please

 

[Juha]

British should only have been far-sighted and should have ordered some Vickers Model 1931 AA guns for themselves before the war as interim AA gun before 3.7" AA gun was ready. In Finnish army our version, 76 ItK/34 V, Vickers got later 76 psa Vj4 armour piercing tracer (AP-T), the projectile weight 6.5 kg and it had muzzle velocity of 750 - 790 m/sec. Rumanian 75mm version also had AP ammo and it was used in A/T tasks few times.

Juha

 

[Shortround6]

The problem with using some of these AA guns, even just the barrels and breeches with new recoil mechanisms and carriages is that metallurgy was making big strides during the 20s and 30s. WW I and 1920s designs had rather heavy barrels compared to some WW II guns. Compare the US 3in tank and anti-tank gun with the 76mm gun. Despite using a working pressure 25% higher the 76mm barrel is hundreds of pounds lighter. The US 3 in is a WW I coast defense/AA gun.

Using AA guns for AT work is a sign of desperation and/or things have really dropped in the pot. Troops at the front will use what they have and DP or even "triple threat guns" look good to the people at home ( and to politicians) in propaganda pieces but using AA guns to shoot tanks is a waste of resources.

 

[Shortround6]

The 'Anti tank weapons' by Chamberlain Gander gives 2,9 tons as 'in action' weight of the 17pdr.

I will agree that the 17pdr went 3 tons or so. Perhaps the version on the 25pdr carriage is were the lower weight comes from?

The 17pdr could do at 900 meters what the Pak 40 could do at 100 meters using similar projectiles though.

 

[Njaco]

Using AA guns for AT work is a sign of desperation and/or things have really dropped in the pot. Troops at the front will use what they have and DP or even "triple threat guns" look good to the people at home ( and to politicians) in propaganda pieces but using AA guns to shoot tanks is a waste of resources.

But isn't that exactly how the German 88 became famous?

 

[Shortround6]

It became famous but it really wasn't a good use of resources.

For instance while some of Rommel's 88s were shooting up all those British tanks, British bombers were pounding the crap out of his supply ports.

AA guns in forward AT positions are not tied into the AA net and are not connected to the AA predictor/director which means they are very ineffective AA guns even at defending the front from air attack not to mention the fact that if they at aircraft before the attack comes they revel their position to artillery spotters.

The AA carriage is much heavier (2-3 times) what an AT carriage weighs and much more costly, it requires a bigger tow vehicle. It takes more time to em-place and camouflage.

The 88 gained fame when the Germans had few good 75mm AT guns available and it was the 88 or 37mms in France and the 88 or 50mms in North Africa and Russia. Once it had the reputation it kept it and the later bigger 88s added to it but using the full AA guns had never been a really good idea.

 

[Juha]

The problem with using some of these AA guns, even just the barrels and breeches with new recoil mechanisms and carriages is that metallurgy was making big strides during the 20s and 30s. WW I and 1920s designs had rather heavy barrels compared to some WW II guns. Compare the US 3in tank and anti-tank gun with the 76mm gun. Despite using a working pressure 25% higher the 76mm barrel is hundreds of pounds lighter. The US 3 in is a WW I coast defense/AA gun.

Using AA guns for AT work is a sign of desperation and/or things have really dropped in the pot. Troops at the front will use what they have and DP or even "triple threat guns" look good to the people at home ( and to politicians) in propaganda pieces but using AA guns to shoot tanks is a waste of resources.

Vickers gun was very early 30s design, and what I was thinking is an A/T vehicle like Archer or German Marders, so ritish would have had heavy SP A/T gun capable to easily knock out Mk IIIs and IVs which also had capability to knock out A/T guns with a good HE round.

Also it might have been used as a basis of heavy tank gun like Germans used their 88 Flak gun for theit 88mm tank gun
Juha

 

[Vincenzo]

I will agree that the 17pdr went 3 tons or so. Perhaps the version on the 25pdr carriage is were the lower weight comes from?

i think from people that not understand difference from carriage weight and weapon weight. the 25 pdr carriage weight around 4000 lbs with 17 pdr gun are almost 5800 lbs (just taking no modification).

 

[Shortround6]

The complete 25pdr gun went 3968lbs. the barrel and breech went 1000lbs. SO a 25pdr carriage without barrel and breech would be under 3000lbs( 2968lbs?)

A 17pdr barrel and breech was 1822lbs. So 2958lbs + 1822lbs = 4790lbs ?

17pdr carriage with split trails and 60 degree traverse being much heavier than the 25pdr carriage.

 

[DonL]

I also agree that something similar ton the 7,5cm Pak 40 would be the best.

From weight and performance the Pak 40 is near in it's own class.

6 Pounder: weight 1140kg; performance: 81mm@30deg; 500m (APCBC)
7,5cm Pak40: weight 1425; performance: 109mm@30deg; 500m (APCBC)
17 pounder: weight 3050kg; performance: 140mm@30deg; 500m (APCBC)

The 7,5cm Pak 40 had 25% more weight then the 6 pounder, but 35% more performance.
The 17 pounder had 100% more weight then the Pak 40, but only 29% more performance.

First lets a fact or two straight. The 17pdr did not weigh twice what a Pak 40 did, it weighed about 50% more. It also weighed a whole lot less than than all the rest of the heavy AT guns the Germans dragged onto the battle field, like all those 88mm guns. Like the 75mm/L70 the 17pdr could out penetrate the 88mm/L56 at most normal combat ranges.
The British 6pdr could have been looked at the Germans for a few hints also. When loaded with the same type of projectile as the PaK40 (APCBC) it wasn't that far behind in penetration.

This coment is also not objektive.

 

[Jabberwocky]

17 pounder had an in-action weight of 4,624 lbs, at least according to the Royal Artillery. That's just under 50% more than the Pak40 7.5 cm, which had an in-action weight of about 3,135 lbs.

As for the HV 77 mm coming before the 17 pounder, that's putting the cart before the horse. The 77mm was basically just a cut-down 17 pounder, fitted with the shorter breech from the Vickers-Armstrong 75mm HV project and less powerful ammunition from the 3-inch 20cwt. It was developed precisely because the original weapon was slightly too large to fit British tanks (as was the Vickers-Armstrong high velocity 75mm L/50 gun)

The problem with fitting the 17 pounder into UK manufactured tanks is that UK tanks had turret rings that were too narrow, primarily due to the narrow UK rail gauge and the loading gauge (and thus the width of rail tunnels). The UK War Office change the loading gauge design limitation from 8'9" to 9'6" in 1941 (to accommodate the Churchill) and then dropped the requirement altogether in 1942.

The Sherman, which they managed to just about shoehorn a 17 pounder into (after a pretty significant redesign, including redesigns of the barrel and recoil system), had a 69" turret ring. In comparison, UK tanks had the following turret ring widths:

Matilda II: 54.25 in
Churchill: 54.25 in
Valentine: 57.7 in
Cromwell: 57.2, later 64 in
Comet: 64 in
Challenger: 70 in


The QF 6 pounder (or more accurately its ammunition) was developed significantly and the gun remained a useful AT weapon even against targets in the 45+ ton category to the end of the war. APCR (first issued in late 1943) was credited with 100 mm at 1000 yards/30 degrees from the Mk 4 (L/50). APDS, issued in mid-1944, was capable of 140 mm + at 1000/30, although accuracy was not good, due to variable separation of the sabot. The problem was not as pronounced as in the 17 pounder though.

The gun remained in service with UK and US anti-tank detachments all the way through to the end of the war.

The main problem with the QF 6 pounder is the lack of effective HE, which was more a doctrine issue (in the UK) than an design issue. I believe (but I could be way out on this one) that HE ammunition was first issued for UK guns in March or May 1944, but ammunition was in relatively short supply. HE was used in late 1944 and through 1945 by 6 and 17 pounders for bunker/ hardened emplacement plinking at long-ranges, outside of MG ranges.

 

[Jabberwocky]

17 pounder had an in-action weight of 4,624 lbs, at least according to the Royal Artillery. That's just under 50% more than the Pak40 7.5 cm, which had an in-action weight of about 3,135 lbs.

As for the HV 77 mm coming before the 17 pounder, that's putting the cart before the horse. The 77mm was basically just a cut-down 17 pounder, fitted with the shorter breech from the Vickers-Armstrong 75mm HV project and less powerful ammunition from the 3-inch 20cwt. It was developed precisely because the original weapon was slightly too large to fit British tanks (as was the Vickers-Armstrong high velocity 75mm L/50 gun)

The problem with fitting the 17 pounder into UK manufactured tanks is that UK tanks had turret rings that were too narrow, primarily due to the narrow UK rail gauge and the loading gauge (and thus the width of rail tunnels). The UK War Office change the loading gauge design limitation from 8'9" to 9'6" in 1941 (to accommodate the Churchill) and then dropped the requirement altogether in 1942.

The Sherman, which they managed to just about shoehorn a 17 pounder into (after a pretty significant redesign, including redesigns of the barrel and recoil system), had a 69" turret ring. In comparison, UK tanks had the following turret ring widths:

Matilda II: 54.25 in
Churchill: 54.25 in
Valentine: 57.7 in
Cromwell: 57.2, later 64 in
Comet: 64 in
Challenger: 70 in


The QF 6 pounder (or more accurately its ammunition) was developed significantly and the gun remained a useful AT weapon even against targets in the 45+ ton category to the end of the war. APCR (first issued in late 1943) was credited with 100 mm at 1000 yards/30 degrees from the Mk 4 (L/50). APDS, issued in mid-1944, was capable of 140 mm + at 1000/30, although accuracy was not good, due to variable separation of the sabot. The problem was not as pronounced as in the 17 pounder though.

The gun remained in service with UK and US anti-tank detachments all the way through to the end of the war.

The main problem with the QF 6 pounder is the lack of effective HE, which was more a doctrine issue (in the UK) than an design issue. I believe (but I could be way out on this one) that HE ammunition was first issued for UK guns in March or May 1944, but ammunition was in relatively short supply. HE was used in late 1944 and through 1945 by 6 and 17 pounders for bunker/ hardened emplacement plinking at long-ranges, outside of MG ranges.