Start with 88 gr of H-1000 and work up. Depending on your rifle and lot of powder you have you should fine a sweet spot around 90 to 92 gr. But as always, work up to this.
Lapua Brass and a CCI 250 M primer.
Seat a 300 Berger .015" off the lands and fine tune from there.
Thanks what kind of groups have you guys shot with those loads, i have been playing with the retumbo sitting at 86 gn shooting around 2550 fps, Have you heard of any other loads that might work thanks a bunch