Other rare weapon denominated “panzerbuchsen” even it was more like a light canon was the Reinhmetall- Borsig SPzb 41 ( heavy antitank rifle model 41) wich had a conical bore starting 28 mm and tapered to 20 mm, it shoot a tugsten core round a very very high speed (some like 1400 m/s)
and the ammo.
It was very effective but I guess that the ammo issue must be troublesome after 1943.
The heavy rifle SpzB 41 was the standar armament on the SdKfz 250/11.
and sometimes over the Sd.Kfz 221, this in particular belonging to the African DAK.
German Spzb 41 mounted over captured Bren carrier.
28x187mm rimmed ammunition:
Details and markings of the ammo.
Sprenggranate 41, 139 grams muzzle speed about 1100 m/s.
Detail of the bullet note the soft iron lips wich are “squeezed” to the final caliber, 20mm.
Hartkern panzergranate, Armor piercing hard core tugsten round, 120 grams extremely fast and hard hitting projectile, 1400 and more m/s.
Ammo box (AP)
The cartridge case for this gun was actually based on the French 25x194R anti-tank gun round. The initial development work was done by Larsen of Denmark for the French Army, who tested the prototype in January 1940. The German round was obviously inspired by this, if not a straight copy.
The 75/55-mm AT Gun, Pak 41" from Tactical and Technical Trends
A U.S. intelligence report on German 75/55-mm tapered-bore antitank gun used in WWII, from [i]Tactical and Technical Trends[/i], No. 40, December 16, 1943.
[LEFT]THE 75/55-MM AT GUN, PAK 41[/LEFT]
An account of a new and powerful tapered-bore 75-mm AT gun made by the Rheinmetall factory, the 75/55-mm (2.95-in/2.17-in) Pak 41, has recently become available through Allied sources. The gun has a curious bore; the rear part is cylindrical and rifled; the central part, tapered and unrifled, and the muzzle section – 27.6 inches – cylindrical and unrifled. The weight of the powder charge fired is 95 per cent of the weight of the projectile. With an estimated velocity of approximately 4,000 f/s, and a penetration of 5.94 inches of homogeneous armor at 1,000 yards, the gun is most formidable.
a. General
The 75-mm Pak 41, one of the latest German antitank guns to be brought into service, is the third* of the Gerlich or tapered-bore weapons introduced. In issue No. 7, p. 3 of Tactical and Technical Trends, reference is made to the use of this principle in the 42-mm Pak 41. A 75-mm tank gun, the 7.5-cm Kw.K 41, is also known to exist, and it is very probable that this weapon too is of the tapered-bore variety. The caliber of the 7.5-cm Pak 41 at the breech is 75 millimeters (2.95 in), while at the muzzle it is reduced to 55 millimeters (2.17 in). The reinforced breech is of the vertical wedge type, and is semiautomatic. There is a muzzle brake. The weapon is very long, low and sturdy in appearance. The carriage which has a split trail, is unusual but extremely simple. The cradle is attached to the shield, which forms the basis of the carriage, by what is, in effect, a spherical universal joint. The cradle itself is cylindrical, and covers the whole of the rear half of the barrel. The gun is sighted up to 1,500 meters (1,635 yards), and the sight has four scales for use according to the actual muzzle velocity of the gun, which drops considerably owing to wear. The life of the barrel is provisionally estimated as 500 to 600 rounds.
The shield is composed of 2 1/4-inch plates bolted together with the barrel installed in a ball mount.
The elevating mechanism, of the sector type, is on the right-hand side of the cradle. The traversing mechanism is of the screw type and is on the left. There is no equilibrator. The buffer is hydraulic, and the recuperator is spring type. The wheels are metal with solid rubber tires. Traction is motorized. The axle is under-slung with torsion-bar suspension, which is automatically cut out when the trails are opened. Pneumatic brakes, controlled by the driver of the tractor, are fitted. .
Gun Data
Estimated muzzle velocity 4,123 Length of barrel (approx)170 inWeight in action1.4 tons (British long)Elevation-10° to +18°Traverse60° Height of axis of bore at 0° elevation34.6 inLength of recoil (approx)27.6 in
c. Ammunition
Fixed ammunition is used with an AP tracer projectile of Gerlich design (see accompanying sketch). The AP round is known as 7.5-cm Pzgr. Patr. 41 Pak 41 (Armor-piercing shell Model 41 for Pak 41).
The projectile consists of the outer case (1), the tungsten carbide core (2), the screw-head (3), the ballistic cap (4), and the tracer (5). The outer case has a forward and a rear skirt. Only the forward skirt is perforated. The screw-head is made of mild steel.
The propellant charge is diglycol tubular powder, while the igniter is of pyroxylin porous powder.
There is also an HE round (7.5-cm Sprgr. Patr) (HE shell Model 41 for Pak 41) as in the cases of the 2.8-mm s.Pz.B (antitank gun) 41 and the 4.2-cm Pak 41, but no details of this ammunition are known.
The following are brief specifications of the AP ammunition:
Total weight of round 16.65 lbTotal length of round 29.8 inWeight of projectile 5.68 lbWeight of tungsten carbide core 2.01 lbDiameter of core 1.16 inWeight of propellant charge 5.4 lb
d. Penetration
The following figures for penetration of homogeneous armor by this weapon firing the AP projectile have been estimated:
Range Thickness of armor in inches (yards) 500 (6.67 in) (5.75 in) 1,000 (5.94 in) (5.12 in) 1,500 (5.28 in) (4.49 in) 2,000 (4.63 in) (3.94 in)
It would be interesting to know how many of this were actually deployed.
“Sqeeze bore” guns were always a sort of hot house Lily, the carbide for the shot was an extravagant use for the valuable metal, but it surely got the job done. It was decided later in the war that stocks of T. carbide would be used for tools, and not projectiles, so another type of shot was substituted, (probably some type of steel alloy. ) The fixed composit type of round while a vast improvment over standard steel shot, was still not as ballistically efficient as a discarding sabot type of shot. That is one nice rifle PanzerKnacker! - Raspenau -
Yeap, it was like that, or your have the tools for lathes and mills or you have the tugsten for armor piercing rounds, the germans cant have both.
S.pz.B 41.
The external and terminal ballistics of the squeezebore were pretty much the same as APDS. The internal ballistics were more difficult to compare: the constantly wider bore of the APDS gun was more efficient, but there was the ‘parasitic weight’ of the sabot…
With WW2 technology squeezebore guns did have one advantage, I think - they were probably a lot more accurate than APDS. The big advantage which APDS held is that the gun could fire full-calibre HE ammo.
The Sabot components of APDS were spun off as the round cleared the bore, or soon after, the rigid composit rounds retained the sabot intact throughout the flight to target and would as a result suffer loss of velocity from the extra baggage(like putting a ball bearing in a whiffle ball. ) I do agree that taper bore munitions were more accurate, not suffering any troubles during separation of the sabot parts.
Was the taper bore projo designed to account for the weight of the flanges? being fixed, they would add to the flying weight, unless some metal was removed to keep the weight down.(Just my late night musings.)
The parasitic weight of the sabot concerns the energy required to accelerate it up the bore. Since the sabot is then dropped, that energy is wasted. For example, the complete 17 pdr APDS projectile (inc sabot) weighs 7.7 lbs. The actual penetrating tungsten carbide core weighs 4 lbs. Allowing for the fact that it also carries a nose and rear sheath, the flight weight of the projectile will be about 5 lbs. So the gun has to accelerate 7.7 lbs up the barrel, of which only 5 lbs proceeds to the target: so about 35% of the propellant energy is wasted.
There is no such loss with squeezebores, the entire projectile flies through the air. Unlike APCR/HVAP (which is like APDS except that the sabot stays attached to the penetrator) the flange is squeezed flat against the penetrator so doesn’t cause significant added drag; the aerodynamics are about the same as with APDS. There is probably extra friction in the barrel as the flanges are squeezed down, but I have no data on that.
The users of British armoured cars armed with 2 pdr guns fitted with Littlejohn squeezebore adaptors found it a nuisance that they had to unscrew the muzzle adaptor before they could fire full-calibre HE shells. So some of them left the adaptor off all the time and just fired the squeezbore shot “unsquoze”, so to speak, as if it were APCR. This seemed to work well enough at normal ranges, although there would have been a significant loss in velocity at longer ranges as the flanges were still sticking out into the air.
It would be very interesting to see comparative velocities and penetration figures at different ranges for the squeezebore shot fired with and without the Littlejohn adaptor, but I don’t know if that was ever done. I suspect that the velocity without the adaptor might have been slightly higher at short range because of the reduced friction.
Thanks for defining the terms you used, it helps alot. I do remember the Littlejohn adaptor, and that it wasnt very popular.
is there any data concerning bore wear with the squeeze bore Vs. the straight bore? not anything extraordinary, just the usual shot to shot wear that one had to compensate for as the tube went through its usable life.
In some cases, there would be different wear factors ascribed to different types of munitions depending on their powder charges. In the US, this was called E.F.C. , (dont remember what it stands for) each type of round was given an EFC value, to help determine bore wear for each shot expended. I think the EFC value was based on the wear produced by a theoretical “round” ,and the others were compared to it. - Raspenau -
I have no data on bore wear for squeezebores, but I would expect it to be greater than usual because of the need to squeeze down the steel flanges: particularly in the case of the add-on Littlejohn adaptor, as the shot would already have been travelling flat-out when it hit the adaptor.
You can see some illustrations of the 2 pdr ammo in [b]THIS[/b] article on my website.
EFC stands for Equivalent Full Charge. It was based on the most powerful (and therefore erosive) charge used in the gun: reduced charges could achieve multiples of this. So a battleship gun might be rated, for instance, as good for 300 maximum-power AP shots before the barrel needed relining; the life was therefore rated at 300 EFC. For shore bombardment they would used lighter HE shells with a reduced charge, which might be good for 10+ times as many shots.
You are wise beyond years, I will surely have a look at the link, Thanks a bunch! - Raspenau -