What was the "Taper-Bore" Anti Tank Gun?

Was it any useful?

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From what I've read, (and what I can remember), it was a concept that never made it into widespread production. Essentially it is a normal cannon that decreases slightly in diameter nearer to the opening. The idea was to increase pressure as a projectile moved out of the barrel during firing, thus making a projectile with higher penetrating power or greater range. Apparently the concept did indeed work, but it was so damaging to the barrels that the need for barrel changes/repair made the concept impractical. I have a book somewhere that covers this, but I think it's in Toronto. I'll bring it with me next time I visit my brother. I hope this helps a bit, but remember, this is from memory, so you can't quote me or hold me to any of this your honor!

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"The only good is knowledge and the only evil is ignorance." Socrates

Otto's right - the Germans used the tapering-bore ( or 'squeeze bore' )facility with the 2.8cm schwere Panzerbuchse 41 . It was a small, light a/t weapon and apparently when it was introdued ( 1941 ) it was reckoned to be quite effective. It was originally designed for use by Fallschirmjager.

The round tapered from 28mm to 20mm when fired.

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The big problem for Germany with the taper bore was the eventual running out of Tungsten supplies required for ammunition production. The 'squeeze bore' is a slightly different thing, the gun only tapers for the final length of the barrel such as in the PAK 41 where the last section of the barrel was a detachable squeeze that could be easily replaced.
Cheers,
Adam

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I see cool.

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Otto has it essentially correct. The concept was that the gun fired a shot similar to a modern sabot round. That is, a round that had a soft ring of material surrounding a hard sub-caliber shot. The difference was that in the taper (or squeeze) bore gun the soft outer ring was squeezed down by the barrel taper until it reached the size of the hard core shot. This allowed for more velocity through a larger volume of gas to push against the shot.

This system was tried on four guns during WW 2; three German, one British.

The first was the 2.8cm S PzB 41. It squeezed the shot from 28mm in diameter to 20mm at the barrel with a 1402 m/s muzzle velocity. This gave it about half again the penetration of a conventional 20mm cannon.

The second was the 4.2cm le. Pak 41. This looked like a 3.7cm Pak gun except with a longer barrel. It used the same principle with the shot going from 42mm to 30mm at the muzzle. The muzzle velocity was 1265 m/s and it had about double the penetration of a 37mm gun and almost equaled the performance of the 50mm Pak at out to about 500 yards.

The third German gun was the 7.5cm Pak 41. This was Krupp design (for obvious reasons given below), and only 150 were produced. This gun fired a 75mm round that reduced to 55mm at the barrel. Its muzzle velocity was 1124 m/s and it had a penetration almost equal to the 88/71 on a Tiger II out to about 1000 meters. A major problem was that the gun had a barrel life of just 400 rounds at most (about a tenth of a normal cannon of that size).

The problem for both of these was first that Krupp through its subsidiary Hartzmetallzentrall controlled all of the tungsten carbide production in Germany. This created an artificial shortage and raised the cost of ammunition substancially for these guns through the monopoly this company had. This made them uneconomical to use as well as making ammunition scarce.
The second problem was that the barrels wore out very quickly in use. The combination of pressure and velocity were very hard on them. The result was that only a relative handful were built and those that were saw relatively little service before being scrapped.

The last squeeze bore weapon was the Littlejohn adapter for the British 2pdr gun. This came out late in the war as a means to give a bit more punch to armored cars still using the 2pdr. It was a bolt-on assembly that lengthened the barrel of the gun and worked on the squeeze bore principle. The reduction was far less radical than in the German guns only reducing the shot to about 35mm. But, it precluded using regular shot or HE rounds so it saw little service. A few were also fitted to US 37mm guns on armored cars in British use as these could still fire their regular rounds using it. It helped a bit with muzzle velocity but not significantly.

A picture from the Ammunition Photo Gallery on my website, showing some different types of WW2 subcalibre rounds (mostly not squeezebore):



20x138B (German 2 cm Kwk 30/38 APCR), 37x94R (French 37mm Mle 1935 APCR), 28x187R (German 28/20mm PzB 41 - Gerlich squeezebore), 37x249R (German 3,7 cm PaK 36 Pzgr.40), 37x263B (German BK 3,7 Pzgr.40), 40x304R (British 2 pdr APSV Mk 1: Littlejohn squeezebore)

In the pic below of the projectiles, the one at the left is a sectioned example of the 28/20 PzB 41: you can see the penetrating core, and the "skirts" which were squeezed flat as the projectle went down the barrel.



Finally, an unusual Littlejohn round, intended for the 40mm Vickers Class S fitted to the Hurricane IID and IV "tankbusters". It was never adopted. There's an article about it on my website:

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