autogun

Military Guns and Ammunition

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This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons.

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The Foresight War Revisited: Artillery   Novel: The Foresight War

Started 16-Feb by autogun; 5360 views.
17thfabn

From: 17thfabn

24-Mar

Would APCR / HVAP been simpler to produce? 

With APCR / HVAP can you use materials other than tungsten alloys? Seems tungsten was in short supply, expensive and a critical material. 

autogun

From: autogun

25-Mar

Yes and yes. You will find I have already discussed both of these in previous posts.

My preference in terms of development order would be:

1. APCR using steel penetrator

2. APCR using tungsten penetrator (same weight projectile - more slender penetrator).

3. APDS

That should allow a steady improvement in performance, with APDS being adopted once it has been thoroughly debugged.

Refleks

From: Refleks

26-Mar

Why wasn't HEAT more commonly used in large caliber guns when shaped charges were used often in lower velocity applications?   Was it a fuzing problem as velocity gets higher?

RovingPedant

From: RovingPedant

26-Mar

I’d hazard it’s more of a case of diminishing returns. Early shaped charges were not so efficient, proper stand-off distance wasn’t well understood and requires expensive fuses, explosive and assembly, so once you get beyond a certain muzzle velocity you’re better off using solid shot from a cost and performance point of view.

 

hobbes154

From: hobbes154

27-Mar

Refleks said...

Why wasn't HEAT more commonly used in large caliber guns when shaped charges were used often in lower velocity applications? 

Caliber or velocity?

For caliber, I would guess as you get to 6" or so any kind of specialist AT shell is redundant through sheer size.

For velocity, as well as what RovingPedant said, my understanding is HEAT performance is degraded by rapid spin, so it didn't work well in high velocity rifled guns until slipping driving bands were invented. (Does this actually make sense? I also thought higher velocity guns deliberately had less rifling twist since the rate of spin needed to stabilise a projectile does not rise with, or at least is not proportional to, velocity?)

autogun

From: autogun

27-Mar

tomo_pauk said:

autogun said: If you take the 17 pdr AT gun's cartridge case and neck it out to the same calibre as the 25 pdr (87mm), the resulting ballistics will be a close match for the German 8,8 cm L/56.

If not better than the 8.8 L56, that have had ~2.7kg of propellant (biggest charge), vs. 4 kg for the 17pdr (also biggest charge). Granted, the HE shells taken from the 'normal' 25pdr will not be using more than 1.5 to 2 kg.

This is an interesting issue: there are two basic ways of estimating the performance of the "87mm" (17 pdr case necked-up to take 25 pdr shells). One is to calculated the muzzle energy of the 17 pdr, which comes to about 3,000 kJ. Then allow for the increase in calibre improving the efficiency  - say, around 3,400 kJ. This would mean the the 87mm would drive the 25 pdr HE shell (11.3 kg) at about 775 m/s, and the 25 pdr's 9.1 kg shot at around 865 m/s.

The German 88mm L/56 fired the standard 9.4 kg HE shell at 820 m/s for 3,160 kJ. So the 87mm would be better, but not that much better. However, when you compare the cartridge cases, that of the 17 pdr is significantly bigger than the 88mm L/56: compare 88x571Rx111 (rim) with 76x583Rx135. This backs up your comment about the propellant weights. By this score, the 87mm should be considerably more powerful. The most obvious reason is that the Germans used relatively longer barrels to obtain more performance. The other possibility is that the Germans used higher loading pressures, but I don't think they did.

Thoughts?

.

Red7272

From: Red7272

27-Mar

autogun said:

Thoughts?

From Naval Weapons of WWII the Brits used much higher chamber pressures than anyone else. So the only real conclusion is that the 17 pdr is so stupidly overbore that necked up to 87 mm with a longer barrel ME it would be more like 4,000 Kj than 3,400 Kj and give an MV of about 930 mps. This closer to the 20 pdr performance so sounds plausible.

  • Edited 27 March 2021 17:01  by  Red7272
larrikin2

From: larrikin2

28-Mar

Having visions here of a Firefly putting one in one side and out the other of a Panther, drilling the engine in the process, and the "WTF was that?!?!?" reaction from the panzertruppen. :D

autogun

From: autogun

28-Mar

OK, so let's add another couple of comparators:

British 20pdr tank gun (Centurion III, 1948): 83x618Rx147; 9.1 kg APCBC @ 1,020 m/s = 4,730 kJ

Pak 43 L/71 AT gun (Tiger II): 88x822Rx146; 10.4 kg @ 1,000 m/s = 5,200 kJ (6.8 kg propellant)

and finally, as a direct comparator with the 17pdr:

75mm L/70 KwK 42 (Panther tank): 75x640Rx122; 6.8 kg @ 936 m/s = 3,000 kJ

So there's an exact match between the 17pdr and 75mm L/70. I don't know the propellant weight for the 75mm, but given that the rim diameter is smaller but the case is longer, there's probably not a big difference although I suspect that the 17pdr has a bigger capacity (but a shorter barrel, of course).  

 Comparing the 88mm L.71 with the 20pdr, the rim diameters are the same but the 20pdr case is only about 75% of the length, while producing 90% of the ME. I don't know what the calibre length of the barrel was...

Barnowlgreen

From: Barnowlgreen

28-Mar

Hi,

The 20pdr had a length of 66.7 calibres, or 226.4 in .

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