wrong calibers

[yacinator]

how come the 28mm antitank rifle have the caliber of 20mm? how come the 42mm antitank gun has the caliber of 29.4 mm? plz help

[Redwolf]

The barrels get narrower to the front, firing a round with a disgarding hull around an undercaliber core (SABOT).

[flamingknives]

Technically it's known as a squeeze-bore gun, firing Armour Piercing Composite Non-Rigid (APCNR). It's slightly different to Sabot type rounds (APDS) in that the material that makes the round full calibre (at the start of the barrel) is compressed down and leaves the barrel with the projectile core, albeit squashed down to the final calibre.

[Beer]

Interesting, I was wondering the same thing.

[yacinator]

oh i get it u get the powder charge of a 40mm and the smaller air resistance and higher velocity of a 29.4mm. just one techical question : why not just use bottle neck rounds instead of squeezing the shell down?

[Michael Emrys]

It is advantageous to have the area of the base of the shot be as large as possible while it is still in the gun. That's the same logic behind DS shot as well.

Michael

[Guest Mike]

I think that a bottle-neck round requires much more strength at the breach than a squeeze bore - the same amount of gas is expanding into a smaller volume with a bottle neck, hence you get higher pressure.

By having the larger base you can get the same amount of force onto the projectile by having a lower pressure over a wider area.

[yacinator]

ok

[Michael Emrys]

Originally posted by Mike:

By having the larger base you can get the same amount of force onto the projectile by having a lower pressure over a wider area.

Or alternatively (and the real reason), you get a higher MV for the same pressure. Everybody was looking for ways to increase velocity and this was one approach. The downside is that it is much more difficult and expensive to machine a tapered bore than a straight one. I suppose they might also tend to wear faster, but I don't know anything definite about that.

Michael

[Redwolf]

OK, so if I understand this correctly, then the soft material put around the actual projectile is just squeezed to the projectile and never lost, flying into the target, correct?

What kind of material is that?

It would have to be strong enough to withstand the blast from the propellant but at the same time not absorb major amounts of energy to compress and it would have to compress very well, not re-expanding in flight, not even partially (that would ruin accuracy).

[WWB]

IIRC, usually malliable, softer metals. Like lead.

WWB

[flamingknives]

It's also not a solid driving band, but a truncated cone wrapped around the projectile, so the material isn't so much compressed as folded out of the way.

If it were sheared off completely, it would end up fouling the gun very quickly

[Dandelion]

Edited away as I suddenly realised I was answering the wrong questioin here...

[ April 23, 2004, 05:14 PM: Message edited by: Dandelion ]

[Paco QNS]

The big brother was the PAK 41, a 75 mm version of the taper bore guns.

Only 150 built -due to the scarcity of the wolfram/tungsten, best used for machinery and other more vital needs than killing enemy tanks- (not so in the view of their sufferers).

Photo in les canons à tubes coniques

LemaireSoft's Taper bore gun

----------------------------------

Not totally related, but in the field of innovative artillery, must be cited also the High/Low presion guns, such as the german

PAW 600 (and modern Cockerill 90 mm gun or the M 79 "Blooper" 40 mm grenade launcher) :

Probert Encyclopaedia: Artillery see PAK 41 and PAW 600

Infantry Guns and Heavy Mortars by Phil West

Not exactly the "bottleneck chamber" suggested earlier, but a sort of spigot gun combined with a normal barrel with a special chamber, if I am understanding it correctly.

[MikeyD]

I recall back in CMBB I begged and pleaded BFC to change the 20mm designation to 28mm but it was no go. Their logic was that was the final diameter of the shell and that's that. I countered (unsuccessfully) that by this logic 2 pdrs with Littlejohn adaptors should be listed as something smaller than 40mm, too!

[flamingknives]

They are. The main armament of Daimlers with adaptors is given as being 30mm.

[yacinator]

nice pic Pac QNS

[PS]

If it is of any interest a 77mm round is being sold on eBay:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=585&item=2240912099&rd=1

[flamingknives]

Great, that's apparently illegal in th UK.

I can only assume that it's in a firearms section.

[PS]

No, in the collectable section and sorry its only the shell. I don't think it was for the SG113 as this was a recoiless gun and could not have squeezed this down. It does look like the photos and diagrams of APCNR I have seen. The front holes are to let the air out as it went through the cones.

Does anyone knows if the resulting round had its accuracy affected by being squeezed. I mean as the front edge will have rifled grooves cut into it will this affect the flight characteristics and it would have to be squeezed dead central or the round would arc (a problem with sabot rounds). A normal shell's shoulder sits on the rifling lands and the driving band cuts into it. Possibly difficult to tell as these guns could only fire APCNR but is there any accuracy data on this. What about the 2-pdr littlejohn. Was the APCNR less accurate than AP shot, some crews removed it and fired the APCNR as APCR.

[ May 03, 2004, 07:22 AM: Message edited by: PS ]

[flamingknives]

Squeeze-bore guns could only fire APCNR (Armour Piercing Compisite Non Rigid).

As the muzzle end is pretty much the same size as the tungsten core, I don't think that there would be an accuracy issue, with Littlejohn adaptors or full barrel squeeze bore guns.

Some crews removed the Adaptor to be able to fire APCNR as APCR as well as HE shells.

[PS]

Sorry was in a hurry and didn't check it, corrected the APCR and APCNR. Thanks.