Cover your eyes — he’s gonna open it!

[P0H0]

I think the OP was confusing "N.C." as "non-corrossive" instead of nitro cellulose. It's the erosion in the leade or throat of the barrel from cordite that causes instability of boat tail projectiles. It's unfortunate that no manufacturer makes ammo loaded with a flat base 174 grain Mk.7 projectile. The 174 grain boat tails are Mk.8 specification. It's what's available because the factories in Yugoslavia, (now Serbia/PPU), and Czechoslavakia, (now Czech Republic/S&B), were set up to produce MG ammo when they were doing it for military use.

I sure did — learning new things everyday.