At the core of the Vickers machine gun was the barrel. It is the key component that makes it a firearm. When firing ammunition, the bullet going down the barrel causes wear to the rifling. As this rifling wears, the barrel loses accuracy. Therefore, spare barrels needed to be carried with the gun. One of these was carried in each transit chest. There was also a spare barrel carrier to be used with the packsaddlery or to protect the barrel in transit. The number of barrels carried was determined by the Equipment Regulations. As of July, 1922, this was four barrels, including the one in the gun.

(i) Two new barrels distinguished by a band of white paint round the centre, to be kept in mobilization, one in the gun and one as spare.

(ii) One serviceable barrel for use in peace, for ball firing only; to be returned to store on mobilization.

(iii) One D.P. barrel for use in peace for drill purposes, or for firing blank only; to be returned to store on mobilization.

Army Order 280 of July 1922.
  • Cat No. C1/BD 0604, List of changes A7792, A8961, and A9435, GUNS, MACHINE, VICKERS, .303-IN., MK. I, Barrels, MK. II – For Mks. I, IV A and IV B guns. Without asbestos packing in cannelure
  • Cat No. C1/BD 0605, GUNS, MACHINE, VICKERS, .303-IN., MK. I, Barrels, MK. II, D.P.B. – For Mks. I, IV A and IV B guns. For use with muzzle-attachment, blank

The barrel, specially choked at the breech, is marked “D.P.B.” on the trunnion block. The service barrel in the gun must be replaced by the D.P.B. barrel when the gun is required for firing blank ammunition.

War Office, 1940a
  • Cat No. C2/BG 0195, GUNS, MACHINE, VICKERS, .303-IN., Barrels, Mk. III – For Mks. VI, VI* and VII guns
  • Cat No. C2/BG 0196, List of changes B 235, GUNS, MACHINE, VICKERS, .303-IN., Barrels, Mk. III, D.P.B. – For blank firing. For Mks. VI, VI* and VII
  • Cat No. C2/BG 0566, List of changes B 1449, GUNS, MACHINE, VICKERS, .5-IN., Barrels, Mk. I*


Cleaning a Vickers machine gun barrel was a relatively simple affair, using the cleaning rod or the pullthrough. The cleaning rod was carried in the transit chest with each gun and the pullthrough was part of the spares part wallet or case.

Sometimes it was necessary to use water to help clean and boiling the barrel was the traditional method for all small arms. It was found though that this did not remove metallic fouling from cupro-nickel cases. The build-up of this fouling needed a specific solvent, as described in Army Order 108 of February 1939.

108. Cupro-nickel Solvent for Cleaning Machine Gun Barrels.

1. To enable metallic fouling in machine gun barrels to be removed, the following ingredients and stores for the preparation and use of cupro-nickel solvent will be held by the R. Tank Corps Centre, Bovington, the Small Arms School, Netheravon, and all R.A.O.C. central armourers workshops.

Section H1, Ammonia-Liquor

Section H1 (Not in Inventory), K.N.S. Tablets – bottles of 100

Section K (Not in Inventory),

Funnels, glass (to be provided locally)

Measures, glass (100 c.c. capacity) (to be provided locally).

2. In the case of units other than those detailed in paragraph 1, the removal of metallic fouling in machine gun barrels will be carried out in the nearest R.A.O.C. central armourers workshops.

3. Directions for the preparation and use of the solvent are given in the appendix to this A.C.I.


Cupro-nickel Solvent for Cleaning Machine Gun Barrels.

Directions for Preparation and Use.

1. Preparation of cupro-nickel solvent. – The solvent is prepared by dissolving the K.N.S. tablets in 20 times their weight of dilute ammonia (one volume of .880 ammonia diluted with one volume of water) or since, each small tablet approximates in weight to one gramme, the solvent may be made by dissolving two tablets in 40 c.c. of dilute ammonia, of any multiple of this proportion. 40 c.c. of the solvent is the average quantity to fill a .303-in. barrel, and 110 c.c. for a .5-in barrel.

The solution of K.N.S. tablets is much hastened by crushing before being dissolved in the ammonia.

The solution of K.N.S. tablets in ammonia does not keep well; therefore no more solvent will be made than is required for immediate use.

2. Preparation of barrel for cleaning. – The barrel is cleaned best, with cupro-nickel solvent, when it was cooled immediately after firing; if this is not possible, and any lubricant is in the barrel, the barrel will be cleaned first with flannelette and pullthrough to remove the lubricant.

Plug the chamber end of the barrel with a cork, and stand in a vertical position. If the barrel has a gas vent, the latter will be closed with a wooden plug.

3. Cleaning. – A glass funnel is placed in the muzzle and the solvent poured in slowly. on no account will the solvent be allowed to run down the outside. The solvent must be left in the barrel for three or four hours.

The solvent is then run off and the barrel well washed our with water, thoroughly dried and lubricated.

If necessary, repeat the above process with fresh solvent until the barrel is clear. The removal of cupro-nickel is greatly assisted by use of the pullthrough and gauze wire after each application of the solvent.

4. Special points to be observed. –

Use ammonia of the stated strength (.880 ap. gr.) only. Weak ammonia must not be employed.

Do not reduce the quantity of ammonia below the stated proportions.

The tablets and solvent are poisonous.

Keep all bottles well stoppered.

After the solvent has been run off from the barrel, wash out the barrel thoroughly with water.

Thoroughly dry the barrel before lubricating.

Army Council Instruction 108/1939, February 1939.

Barrel Life

In one of our question and answer videos, Rich answers the question (with the information he had available at the time).

The actual life of a Vickers barrel has many variables: rate of fire, type of ammunition, construction, heat accumulation, level of water and others. Therefore, it is not possible to provide an accurate value; however, the first guidance based on Mark VIIIz ammunition was provided in Army Council Instruction 415 of April 1940.

415. Life of .303-inch Vickers M.G. Barrel.

Investigations regarding what may be considered to be the safe life of a .303-inch Vickers M.G. barrel when firing Mark VIIIz ammunition have shown the life to be in the vicinity of 10,000 rounds.

When a barrel has fired 10,000 rounds of Mark VIIIz small arms ammunition at the rates of fire likely to be maintained in prolonged barrage or counter preparation programmes, the barrel wear is liable to be such that the safety of our own troops cannot be absolutely guaranteed.

It has been further ascertained that when this life is exceeded at such rates of fire there arrives a time when the barrel rapidly becomes very unreliable. The safe barrel life will therefore be regarded as 10,000 rounds and estimates for barrel expenditure will be based on this figure.

A simple barrel log of rounds fired will be kept.

Army Council Instruction 415 of 1940.

Ten thousand rounds became the figure for barrel replacement calculations to ensure that the safety limits weren’t affected. It was found that when firing Mark VIIIz ammunition, there wasn’t any indication of accuracy loss until the ‘collapse.’ Whilst this maintained accuracy, it meant that there wasn’t any early warning.


  • The National Archives, WO 123/63 Army Orders 1922.
  • The National Archives, WO 293/24 Army Council Instructions 1939.
  • The National Archives, WO 293/25 Army Council Instructions 1940.
  • War Office, 1940a; 1942; 1944c; 1949a