303 British Chamber Diagram

[Bindi2]

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I have used Mk6, M7 and others that i turned into Open Based projectiles with NC powders with OK results. Not to 1000yds. The open base with a deep pocket pushed like Mk8s worked. BTs were just not there. Hornady produced an OBBT .. When turned into a Mk7 was pretty dam good.

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[Alan de Enfield]

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I have used Mk6, M7 and others that i turned into Open Based projectiles with NC powders with OK results. Not to 1000yds. The open base with a deep pocket pushed like Mk8s worked. BTs were just not there. Hornady produced an OBBT .. When turned into a Mk7 was pretty dam good.

Yes - BT bullets and NC powders are usable and can give good results - but, not if the 1st 3" or 4" (or more) of rifling no longer exists, having been burnt out using cordite.

That is why the 'simple barrel check' of pushing a 303 bullet into the muzzle does no good at all. It may be fine for rifles that have shot NC but a rifle that has spent its life shooting cordite can have a perfect muzzle and no rifling from the throat forwards.

It is interesting that similar information is provided elsewhere :

2) Mark 7 .303-in S.A.A. has a cordite load and a flat based bullet. He same applies to .303-in tracer and .303-in AP

Mark 8Z .303-in S.A.A has a neonate load and a streamline based bullet. Trial firings have proved that these two types of ammunition do not wear the barrel in the same manner. Barrels which have been used for Mk.7 or .303-in Tracer or AP become inaccurate much sooner when Mk8Z is used in them, than barrels in which Mk8z only has been employed.

3) One of the advantages of Mk8Z ammunition is that the barrel maintains accuracy and elevation until the actual moment of collapse. No indication of approaching barrel failure is given when Mk8Z ammunition is used. Accuracy is liable to break down very suddenly and the barrel becomes dangerous for use for overhead fire in the later stages of its life. To ensure the safety of our own troops during overhead fire by medium machine guns, the life of a .303 Vickers gun barrel using Mk8Z S.A.A has, therefore been fixed at 10,000 rounds (or 40 belts). This figure is well within the number of rounds successfully completed by the earliest failure of barrels firing an endurance and accuracy test under conditions of excessively rapid rates of fire. If, however, even a few rounds of cordite loaded S.A.A. are fired, the Mk8Z accuracy life drops considerably.