.50 inch Browning Proof & Blank
Proof
No British designed or manufactured Proof ammunition seems to have existed until after WW2.
.50 inch Browning M2 guns were extensively used by the British during the war so it must be assumed that when guns were repaired and re-proofed American made proof ammunition was used.
The American M1 proof cartridge utilised a case of heavier construction than the normal round and was tinned for identification. Early examples included the word "TEST" in the headstamp but most have a normal headstamp of manufacturer and date. Its formal title was "Cartridge, High Pressure Test M1"
The bullet had a gilding metal envelope with a flat base and lead core. Early examples weighed 1,014 grains but most later production weighed 999 grains.
The pressure was set at approximately 62,000 psi.
British Proof
The earliest reference to British high pressure proof cartridges is an order for 30,000 rounds in May 1953. These were described as ".50 inch Browning High Pressure Mark 3 Ball cartridges" and were loaded to give a pressure of 26 tsi. Further orders in 1960 still used the same title but were loaded to a higher pressure of 29 tsi.
These rounds did not have copper washed cases but had a normal ball Mark 3 headstamp with a yellow annulus to denote proof rounds.
Left: .50 inch High Pressure Ball Mark 3. Right: label for same.
An experimental proof cartridge entitled "X4E1" appeared in October 1961 and this had a normal case, copper washed for identification and loaded with a 710 grain ball bullet.
The propellant charge was 248 grains of NRN 151 powder which produced a pressure of 29 tsi. A further order for the X4E1 was given in February 1962.
Proof L12A1
"Round .50 inch Browning Proof L12A1" was approved about March 1964 and was effectively the approved version of the X4E1..
It utilised a standard case and was copper washed for identification. It included "L12A1" in the headstamp and usually had a yellow annulus, although some had a purple annulus.
It had a normal 710 grain ball bullet and the propellant charge was 242 grains of nitrocellulose designed to give a pressure of 19 tsi.
Blank
No .50 inch Browning blank has been approved for British service, although some interest was shown at the end of WW2 and two designs were produced experimentally in 1945.
Design D6/L/163 covered a blank with an extended case to form a mock bullet with a rosette crimp. The drawing was titled "Cartridge Gun Functioning .50 inch Browning" leaving some doubt as to whether this was a training blank or served some other purpose. Cases were made by ROF Spennymore and the headstamp was "SR 45 .50".
The second design consisted of a standard case reduced in diameter at the neck, over which was fitted a rosette crimped mock bullet much in the style of the .303 inch Blank Mark VI. The overall diameter of the mock bullet was 14mm which would have prevented the round chambering in a normal Browning barrel.
It has been postulated that this was a training blank which required the use of a special barrel with an enlarged chamber. This seems highly unlikely as it would not prevent the accidental chambering of a live ball round with disastrous consequences.
Again, these were made by ROF Spennymore and had a headstamp of "SR 45 .50".
There exist other blanks made by Kynoch with a rosette crimp at the neck. These were manufactured in the mid 1960s and often have an L11A2 Observation headstamp. it is believed these were made for the film industry and are not military blanks.