There's a cast bullet company you can locate on the web called "Pb Boolits" that offers a 90gr round nose cast listed as for .30 mauser in a nominal .308, but also offers it in .310 dia...it might work for you....it looks like they make quality stuff in a zillion shapes and calibers....just ordered some .320 cast for my Nambu.... their address is
www.unobtainamite.com