I use .310 in my K98 7.62,
so sizing down what you have should not be a problem, unless the mould has shallow lube grooves,
you should cast a soft lead bullet and force it through and it will give you the size of your barrel,
you may get a surprise at the result,
.311 for .303, most guys size them .313/.314 for lead,
but if it works for you stick with it,
T