Max loads

I'm pretty sure if it's a bolt gun with a 1.2" shank it will be 74 gr for the 300s and it will be 78 gr with the 275 and lighter.I'm sure some of the more experienced shooters will let you know for sure shortly.

Kind of hard to determine the MAX load unless you keep adding powder untilthe barrel blows up? These barrels will withstand a lot of pressure. What will hurt you is a double charge. Those two numbers listed by sa1000 are probably realistic and will give you all the speed and accuracy you need. If you have a good scope with good adjustments, mi dots or hash marks, it is easy to get to the next yardage...............just "click" up!
Two weeks ago I put in a duplex of 6 gr. Clays with 65.8 gr. of H-4198. Then got busy looking and playing with my new Sightron scope for about ten minutes and completely forgot I had already loaded the rifle so I put the SAME load on top of the first. In essence I pushed two 300 gr. SST's plus the second 72 gr. of powder out the muzzle at 3489 fps!!!!!!! Did the barrel blow up? No.................but the dimension in this area was 1.250" and it put a bulge that increased that diameter to 1.270". This barrel was 1.250 for the first 5 inches and then straight tapered to .9 at the muzzle. Total barrel length was 29 1/2". I have since cut 3 1/2" off the breech end so I can get a sabotless bullet down without a loose spot. Yes, it shoots as accurately as before but, I lost about 50 fps for the same load.
Point is..............the fat barrel saved me from what could have been a bloody mess! In my opinion, you could probably shoot 78 gr. of H-4198 all day long with 300 gr. bullets with no problem but just double charge it? And who knows what could happen? Double charging is the BIGGEST source of burst barrels...........not a slightly higher charge. We play with dangerous toys and it is imperative we keep our wits about us when loading and shooting them. Go for accuracy.........not the highest velocity.