In the case of the 303 open base bullet is the means to keep the rifle in action as the base expands to fit the bore and will stay accurate until the rifling is down to about six inches left.
125gn projectiles seldon stabilize unless the barrel is new because they are to short. The 303 never was a varmit rifle even 150gn are suspect over 250yds and in many cases much closer. The rifle design was built around 215gn projectiles then updated to 174gn which is about the limit going lighter.
The Brits fixed the top problem by putting a light tip inside the jacket making the projectile base heavy and long for its weight.