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.303 inch Incendiary

Three designers dominated .303 air service ammunition in WWI, Brock, Pomeroy and Buckingham. Although often referrerd to as incendiaries, the first two of these were really explosive rounds rather than incendiary so have been dealt with under that heading.

The rounds developed by John Buckingham were true incendiaries filled with phosphorus. The earliest drawing of a Buckingham bullet is a Royal Naval Air Service drawing showing Buckingham designs for .303 inch, .45 inch Martini and .707 inch (12 bore). The latter two are described under the "Air Service other that .303 inch" heading.

RNAS Buckingham

It is uncertain whether this early version of the Buckingham actually entered service or whether it was superseded by the Mark I described below.

The case was the normal service ball case and presumably retained a ball headstamp. 

The RNAS design was filled with phosphorus and had the base of the bullet plugged with solder. On firing the solder melted and allowed the phosphorus to escape and ignite in the air.

It is presumed the charge was about that of the ball round but further details are not known.

Detail for RNAS Drawing.

Buckingham Mark I

"Cartridge S.A. Incendiary Buckingham .303 inch Mark I" was approved to desugn RL.23914 but was not shown in Lists of Changes.

The case was the normal service case and is sometimes found with a large "VI" overstamp. It is believed this was in the hope that if captured the enemy would think it was a round nosed Mark VI ball bullet.

The bullet was turned copper and hollowed inside nearly to the tip. it was filled with yellow phosphorus and sealed with a brass plug. Some later examples had an additional lead plug fitted behind the brass plug to improve the seal. The bullet had three cannelures and two small (.03 ") weep holes filled with solder just below case mouth level. It weighed 170 grains and later examples had the bullet nickel plated.

The yellow phosphorus filling gave a clear smoke trace to 1,000 yards.

The propellant was 36 grains of Cordite MDT 5-2.



Mr.Buckingham demonstrating his ammunition at Hythe

The round nosed design gave feed problems in Lewis guns and the RFC requested a Buckingham bullet with the profile of the Mark VII Ball round.

Buckingham Mark VIIB

"Cartridge S.A. Incendiary Buckingham .303 inch (VII.B)"
was approved to designs RL.24642 and IDW 4514 in July 1916 but was not shown in Lists of Changes. The title was later changed to 
"Cartridge S.A. Incendiary Buckingham .303 inch (VII.B) Mark II" and the word "Buckingham" was dropped from the title in 1923 and in 1927 the title was again changed to "Cartridge S.A. Incendiary .303 inch B Mark II". A nitrocellulose version was introduced after the Cordite loaded round and was "Cartridge S.A. Incendiary Buckingham .303 inch NCZ (VII.B) Mark II.z" becoming the B Mark IIz from 1927.

The case was the normal service case and the headstamp included the code "VIIB". A blue annulus was approved in June 1918 .

The bullet had a pointed cupro-nickel envelope and the base was sealed with solder. The composition was held in the forward part of the bullet with two offset lead plugs in the rear. The bullet had one or two weep holes filled with fusible metal that melted at 160 degrees Fahrenheit. The holes were originally .032 but this was later changed to .047". The bullet had no cannelure and weighed about 137 grains, being secured in the case by coning or three pin stabs.

The composition was 10 grains of phosphorus and aluminium powder. It gave a good smoke trace but the effective incendiary effect was about 250 yards.

The propellant charge was 37.5 grains of Cordite MDT 5-2 or 41 grains of nitro-cellulose.

Buckingham Mark III

"Cartridge S.A. Incendiary Buckingham .303 inch (VII.B) Mark III" and "Cartridge S.A. Incendiary Buckingham .303 inch NCZ (VII.B) Mark III.z" were approved to design IDW 4548 (cartridge) and IDW 4549 (bullet) in July 1917 and not shown in Lists of Changes. The title was changed in 1925 to "Cartridge S.A. Incendiary .303 inch (VII.B) Mark III" (or B Mark III.z) and again in 1927 to "Cartridge S.A. Incendiary Buckingham .303 inch B Mark III" (or B Mark III.z).

The case was the normal service case and the headstamp included the code "VIIB". A blue annulus was approved in June 1918 .

The bullet was of pointed form but with a .16 inch (4mm) flat on the nose that was intended to punch a cleaner hole in balloon fabric. The construction was similar to the Mark II bullet but had a single fusible metal filled weep hole. Bullet weight was 147 grains.

The composition was 14.5 grains of phosphorus and aluminium powder which gave a long smoke trace and an effective incendiary range of 500 yards. Bullets during manufacture were tested at 138 degrees Fahrenheit.

Propellant was 37 grains of Cordite MDT 5-2 or 41 grains of nitro-cellulose.

Incendiary B Mark IV

In 1918 a further design was produced to improve the size of the hole punched by the bullet in balloon fabric by having a step on the bullet to act as a kind of wadcutter, The design had not progressed sufficiently at the end of the war for it to see service but work continued after the war in a  somewhat slow fashion.

"Cartridge S.A. Incendiary .303 inch B Mark IV" was finally approved to designs RL 30121 and
DD/L/2014A in 1928 but was not shown in Lists of Changes. 
The nitrocellulose version, "Cartridge S.A. Incendiary .303 inch B Mark IV.z", was approved about 1939. 

The case was the normal service case and the headstamp included the code "BIV" or "BIVZ".  It had a  blue annulus.

The bullet construction was similar to previous marks, apart from the distinctive step just above the case mouth. Also there was a small copper cup between the two offset lead plugs, the upper plug being fluted.
The bullet had no cannelure with two weep holes and the base was sealed with solder. Bullet weight varied between 145 and 154 grains. The incendiary composition was 6 grains of white phosphorus. 


Left: Two experimental WWI period "stepped" incendiaries, forerunners of the B Mark IV.           Right: Incendiary B Mark IV.

Propellant was 36.5 grains of Cordite MDT 5-2 or 36.5 grains of nitrocellulose.

Muzzle velocity was about 2,580 fps.


Incendiary B Mark IV*.z

During the early part of WWII a Kynoch "Trade Pattern" of the B Mark IV was approved as the "Cartridge S.A. Incendiary .303 inch B Mark IV*.z"  Whilst the bullet had a broadly similar external profile the internal construction was different. 

The case was the normal service case and the headstamp included the code "VIIB" or "BZ".  It had a  blue annulus.

The bullet had the same stepped ring as the BIV but in a slightly different position on the bullet. It had a faint cannelure and a single weep hole. Instead of the two lead plugs the BIV*.z had a single fluted plug. In some variants the bullet had a blue tip.

The propellant was 38.5 grains of nitro-cellulose and velocity was similar to the B Mark IV.


Label for Trade Pattern B Mark IV*z Incendiaries.

Incendiary B Mark V

Just before WW2 began an entirely new form of incendiary was under development. This was given the title of “Cartridge S.A.
Incendiary .303 inch B Mark V”
and was a based fuzed incendiary. 

The case was the normal service case and the headstamp included the code "BV".  It had a  blue annulus.

The bullet had a normal Mark VII profile and the forward part of the envelope was filled with the incendiary mix of 3 grains of SR 253 with a 2.4 grain lead azide detonator in the centre of the bullet. Behind that was a striker in a safety collar and the central charge of 7.5 grains of Composition Exploding (CE). The bullet was closed with a lead disc. The whole was reminiscent of the construction of the German 7.92mm B-patrone. 

The SR 253 composition composed 50% aluminium powder and 50% barium nitrate.

Despite being given a formal Mark number, it was realised the bullet was too complex for mass production and it was not introduced to service.               
                                                                                                                                                                    Right: Sectioned B Mark V
Incendiary B Mark VI

In 1938 a Belgian inventor called De Wilde together with his assistant Mr.Kaufmann came to the UK to demonstrate his incendiary and explosive bullets to the War Office. He lived in Switzerland and brought incendiary, explosive and explosive incendiary bullets loaded into 7.5mm Swiss cases. The trial at Enfield was sufficiently successful for the government to reach a commercial agreement with De Wilde in January 1939 and he returned to the UK to work on a .303 version of his design. It soon became apparent from trials that the De Wilde bullets were not as effective as hoped, as they failed to function and bulged the barrels of Lewis guns in the next trials.

De Wilde’s original bullets had all been carefully made and filled by hand and were totally unsuited to mass production so the design was abandoned and De Wilde returned to Switzerland. Meanwhile C.A.Dixon of the Design Department at Woolwich with the assistance of Kaufmann had produced a new incendiary partly based on the De Wilde design. 

“Cartridge S.A. Incendiary .303 inch B Mark VI”
(and VI.z) were approved to design DD/L/10091 in late 1939 and were not shown in Lists of Changes. The design was later superseded by DD/L/10174.

The case was the normal service case and had a  blue annulus. The early examples were unheadstamped in an attempt to maintain secrecy but most carried the code "B.VI" or "B.VIZ".

In the first pattern of bullet the envelope contained a steel sleeve surrounded by a thin lead sheath, the sleeve holding the incendiary composition. The base of the steel sleeve was threaded and the bullet was closed by a slotted brass plug screwed into this. The envelope at the tip of the of the bullet was thinned and had a small hole filled with solder behind which was a small steel ball and anvil to aid ignition. 

It was found that newly manufactured batches of the incendiary composition, SR 365, were more sensitive and did not require the nose to be thinned or the solder filled hole. This second pattern of bullet was to design DD/L/10174 and this simplified bullet was used for most rounds manufactured but no change was made to the nomenclature.

Bullet weight of both patterns was 152 grains with 7 grains of SR 365 containing barium nitrate..

The propellant charge was 38 grains of Cordite MDT 5-2 or 38 grains of nitro-cellulose.

Muzzle velocity was  2,450 fps at a pressure of between 20 and 21 tsi. Some documents state MV was only 2,370 fps.



Incendiary B Mark VII

In early 1941 problems were encountered in service with the brass base plug of the Mark VI bullet becoming detached as the bullet left the muzzle and damaging the aircraft. To overcome this a simplified design was produced in which the steel sleeve was chamfered to the internal shape of the envelope to prevent it moving forward and the base of the bullet was closed with a steel disc over a lead plug.

“Cartridge S.A. Incendiary .303 inch B Mark VII” (and VII.z) were approved to design DD/L/11846 in 1941 and were not shown in Lists of Changes. In Naval service the design was later superseded by NOD 6322

The case was the normal service case and had a  blue annulus. Some early examples were unheadstamped or loaded into cases headstamped "B.VIZ" in an attempt to maintain secrecy but most carried the code "B.VII" or "B.VIIZ".

The bullet had a gilding metal envelope inside which was a steel sleeve within a lead sheath. the bullet base was chamfered and closed with a steel disc and lead base plug. The bullet had a single cannelure and weighed 168 grains. The bullet tio was coloured blue for identification. The composition was 7 grains of SR 365.

The propellant charge was 36 grains of Cordite MDT 5-2 or 35.5 grains of nitro-cellulose.

Muzzle velocity was  2,370 fps.



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