I automatically thought of larger calibres for the Siamese Mauser due to the possibility.

Making one up in a .303 or .30/40 Krag just seemed a waste of a good large bore action.

On the other hand, being a new handloader, one should always start with easier projects where there is a lot of information due to popularity of the round.

With today's modern powders, the .303 in a stronger action, like the Siamese or P14 for that matter, better than factory ballistics are entirely possible.

Even better, is a .308 groove diameter barrel with the .303 chambering, that is, if the chamber is cut for the standard .303's neck diameter - thus all factory .303 ammo can be used along with hand loads using .308" bullets to 220 or 225gr. - whatever is available. Using factory .303 ammo does not develop excessive pressures in the tighter .308" bore as we've tested this here in my friend's rifle. It has a .308" groove diameter X .300" bore diameter but a standard .303 chamber. We merely ground the reamer's pilot to fit the .300" bore. Thus, this P14 rifle is capable of shooting the standard .311" to .312" bullets along with all .308" bullets, from 100gr. to 220gr. He restricts his larger bullet'd loads to factory loaded .303 British - thus lower, entirely safe pressures are being developed.