INTRODUCTION. From the start of the war in 1939, German research personnel working on the projects of developing high-velocity guns and projectiles. In the high-velocity projectile field sub-caliber projectiles were judged by the Germans to show the most possibilities of increasing range and decreas-ing the time of flight in comparsion to stan-dard type projectiles.

Figure 325A – German Flange Geschoss

Three types of sub-caliber projectiles were used: The Pfeilgeschoss which is a fin stabi-lized projectile fired from a smooth bored gun, the Treibspiegelgeschoss of Sabot pro-jectile which is fired from a normal rifled gun and the flange geschoss. The flange ge-schoss is fired from a cylindrical, rifled barrel to which a smooth bored, tapered muzzle extension is attached. This type of projectile is called a "Little-john" by the British and a "Squezze-bore" by other services.

Development and testing of the squeeze-bore projectiles was handled primarily by the private firms in Germany, although all bran-ches of the service were instrested in and advised of the developments. The principal firm working on this project was the Rhein-metall-Borsig Co., although the Krupp Co. and Bochumer Verein Co. both built experi-mental projectiles. The firm of Polte, AG in Magdeburg also built projectiles of this type but had worked only on sizes 5.0 cm and smaller although they were going to build the 5.5/4.1 projectiles which were contempla-ted.

Projectiles of this type were designated to show the original caliber and end caliber of the gun. Thus the 10.5/8-cm squeeze-bore projectile is one which fired from a 10.5-cm gun to which is attached a conical muzzle extension tapered to an emergent caliber of 8 cm.

The principal advantage of the squeeze-bore projectile in comparsion to the other sub-caliber projectiles is that it has no discarding parts.

CONSTRUCTION. The principal source of information on construction details of the Ger-man squeeze-bore projectiles was Dr. Werner Banck. Dr. Banck was in charge of this pro-ject for the Rheinmetall-Borsig Co. for the period from late 1939 through until the end of the war. In the organization chart for the company, Dr. Banck was in charge of the Army high-velocity projectile subsection of the weapons construction and ballistic department of Rheinmetall-Borsig.

Additional information has been gained from interrogation of proving ground personnel at the German Army Proving Grounds at Hillersleben and interrogation of Rheinmetall-Borsig and German Navy ordnance personnel.

Two Flanges. The first type of construction developed employed two solid flanges, for-ward and rear; as Bourrelet and rotating band respectively. This was modified slightly by drilling holes in the forward flange but this type of construction was abandoned in sizes 8.8 cm and above since it proved to be unsatisfactory.

This type of construction proved to be unsatisfactory because it was found that the propellant gases leaked past the rear flange. Then when the projectile passed through the conical muzzle extension the gas was compressed and, even in spite of the drilled holes in the forward flange, large gas pressures were built up (gas pressures up to 6,000 atmospheres were recorded). This resulted in destruction or deformation of the projectile body. Also it was found that at the moment when the projectile left the barrel the extra pressure caused the deformed forward flange to tear and fly off. Several methods of pro-viding a possibility of escape for the enclosed gases were tried other than drilling of the flanges. In the end it was recognized that, in principle, an improvement could be achie-ved only by splitting up the forward guide into individual supports.

Forward Bolts and Rear Flange. The first type of individual forward supports that was at-tempted involved the use of three individual bolts in palce of the forward flange. They were so placed and arranged that they were pressed into the projectile body when the projectile passed through the muzzle squeeze. On the base of the bolts' ribs were arran-ged so that once the bolts were pressed into the projectile body, the ribs caught and the bolts could not be thrown out by centrifugal force.

Since these bolts actually extend into the explosive cavity of the projectile, production of the projectile was considerably complicated. Projectile were actually built in two parts with explosive cavity divided. This made uncertain the complete detonation of the high-explosive filler and impaired the efficiency of armor-piercing projectiles since the cap and nose were weakened.

In an attempt to be able to use normal projectiles an attempt was made to enclose the bolts in individual casings which were screwed or attached to drilled holes in the projec-tile bodies. This eliminated none of the disadvantages of this type of construction and considerably weakened the projectiles due to the drilled hole.

Both of these constructions were made up and fired, in small quantities, in calibers 24/17-cm and 10.5/5-cm size. This construction was abandoned, however, because of the disadvantages. No drawings are available for this type of construction.

To attempt to eliminate the disadvantages invol-ved in the use of long bolts various attempts were made with teles-coping bolts of various types. Some of these constructions were fired but this construction was also abandoned eraly in 1942 in favor of the hollow support studs which have been reconized as the best type of forward support.

Figure 325B – German Flange Geschoss

Hollow Support Studs. The final type of projectile which was built for the squezze-bore guns was the type with socalled hollow support studs. Construc-tion of projectiles of this type was begun in May 1942. Figure 325A and 325B show the 24/21-cm projectile with hollow support studs.

In this type of construction the stud, of soft steel, is pressed into a drilled hole in the projectile body. A sharp edge on the lower protion of stud engages a recess in the drilled hole and thus the stud is se-cured. Then when the projectile is fixed and pas-ses through the muzzle squezze the studs are for-ced down into the drilled holes in the projectile body.

In smaller size such as the 8.8/7.0-cm round only three studs where used, where-as, in lager sizes such as the 24/21-cm projectiles five studs were used. In all cases the studs were wider than one grooves of the rifling with the Germans using in figure of 1/5 caliber for the width of the stud.

The advantages claimed for this type (hollow sup-port stud), are as follows: Considerably less wear of the conical muzzele squeeze.

Use of normal projectile bodies because:

Because of the small depth of the attached studs the projectile body does not need to be thicker than normal.

If the muzzle extension is worn and studs not completely collapsed. The increase in air resistance caused by the protuberance of the studs is considerably less than that cau-sed by a forward flange not being completely collapsed.

Studs weigh less and use less material than the flange.

Less irregular wear in the cone.

Less sensitive to steep in the muzzle piece.

No space is taken from the explosive chamber.

In amor-piercing projectiles the projectile nose is not weakened.

No special machines are necessary to drill the holes for the studs. An ordinary lathe can be used.

All studs for these projectiles were made of soft steel. The most satisdactory method of manufacture was found to be pressing them from sheets and then further pressing of the studs into drilled holes in the projectile body. In this pressing, the material is strained beyound the elastic sumit and, for equal thicknesses, it was the German claim that the studs could be constructed lighter and better since the strength is increased.

Rear Fitting. In all cases the rear fitting was of soft iron. This was the only material made avaible for experimentation due to the German copper shortage. No experimantal work was done with copper or copper alloys. German personnel who have been interro-gated have stated that use of copper might be advantageous and feel that it might allow a larger reduction in caliber. All of them pointed out that the material of the forward studs and rear flange should be the same or trouble would be experienced with heavy erosion in the muzzle extension.

The first method of attaching the rear fitting was to machine a groove around the base of the projectile body, then heat the projectile and press the cold flange in. Trouble was experienced with this system due to the projectile base cracking after cooling and it was abandoned.

The most satisfactory method of attaching the rear flange was found to be that of heat-ing the rear flange to a temperature of 1,120° C and forming it while pressing the flange into the projectile body with a hydraulic press. Pressure used on the 24/21-cm projectile was 400 tons and on the 10.5/8-cm projectile 150 tons. For projectiles ranging up to 8.8/7.0-cm in size ist was expected to press the flanges on without heating them.

Rheinmetall-Borsig shop personnel stated that from the manufacturing standpoint it was found that this system of hot pressing the rear flange on was cheaper than the assembly of ordinary rotating bands.

No manufacturing tolerances were available for either the studs or the rear fittings as no quantity production of these projectiles had been made.

In the conversion of existing projectiles difficulty was encountered only when boat-tailed prokectiles were worked on. Rotating bands, of course, had to be removed.

Explosive Loading. High explosive loaded projectiles were built and fired in all sizes. Wall thickness was the same as ordinary H.E. projectiles and in some cases such as the 24/ 21-cm projectile, existing projectiles were built up by the addi-tion of studs and a rear flange. No special H.E. filler was used. Normal loading (same as ordinary H.E. projectiles) was used.

Fuzing. In the 24/21-cm size the fuzing was a sensitive impact fuze. The 10.5/8 cm was fuzed with the standard 30-second time fuze. Other projectiles were fuzed with impact fuzes and an impact fuze with self-destroying device was reportedly under test. The ef-fect of the muzzle squeeze on the rotation of the projectile was stated to be very little if the squeeze dropped on a ratio of 1-mm with per 30 mm in length. However, if this ratio was changed to 1/50 the revolutions per minute of the projectile was slowed down. Other changes in construction necessary before converting standard fuzes into service in high velocity projectiles were not ascertained.

EXTERIOR BALLISTICS. Muzzle Velocity. The maximum muzzle velocity attained with this type of projectile was stated to be 1,400 m/s; 1,150 to 1,120 m/s was believed, how-ever, to be the most feasible service velocity.

Dispersion. Dispersion with this type of projectile was expected to be as good as that obtained with normal projectiles. Range dispersion of 1 percent was expected and deflec-tion of around 1.5 mm. Actual service test showed frequent wild shots, however.

Change in Form Factor. Lift of the gun was stated as being determined by actual wear on the muzzle extension. For example, the 10.5/8-cm muzzle extensation was changed when 2 mm of wear could be measured. As the muzzle extension wears the studs and rear flange are not completely forced down so a change in form factor results. This change, even if muzzle velocity remained constant, means a decrease in range and an increase in flight time.

German personnel stated that the hollow space formed at the base of the projectile due to the folding of the flanges had an effect of increasing the stability.

Conclusions. The following conclusions have been found on the German high vilocity pro-jectiles of this type designed to be fired from guns with tapered smooth bored muzzle ex-tensions:

Only the 7.5-cm Pak (antitank) gun had been introduced to service. The 10.5/8-cm gun an projectiles were believed to be ready for service but had never gone into production.

Favored construction is the type with collapsing (hollow support) studs forward and soft iron flange pressed on the rear as rotating band.

No material other than soft iron had been made avaible for manufacture of studs and flanges. German personnel feel that copper or a copper alloy might be more statisfactory.

High explosive loaded projectiles were designed for all sizes and fired in all sizes which reached test status. Standard types of H.E. fillers were used and well thickness of the projectiles was the same as projectiles fired from normal guns.