shooting with a 1943 Long Branch nr4 mk 1*

[Brian Dick]

If you're shooting boat tail projectiles, therein lies the problem. Rifles that have been used with cordite will develop a distinct wear pattern in the throat or leade of the barrel. Once this occurs, the boat tail projectiles will not stabilize properly and cause key holing as you are experiencing. Switch to flat base projectiles and your problem should be solved. It's really unfortunate that both the prevalent Privi Partisan and Sellior & Bellot ammo is all loaded to Mk.8 specification which was basically MG ammo designed for the Vickers MMG. Remington/UMC still make a Mk.7z equivalent with the 174 grain flat base projectile if you can find it. If not, try to find some real Mk.7 or 7z military ammo as made by many countries up until the 1980's.