I used the same bullet, as was used back in the 1930s, the VPT/LAPUA D46 weighting 185grn.
Lapua Berdan brass, RWS primer, 46grn N140, OAL 76mm.
Chronoed at 777m/s.
I have still some Lapua Match factory ammo left, it has a muzzel velocity of 748m/s out of the same rifle and used the D47 bullet 185grn.
This M28/30 has the D chamber modification and a groove diameter of .309".
I have one, that has the short throat(wont even chamber a D-cartridge!!!!!!!) and it shoots a tad better
Chris