I think you will find somewhere between 90 and 95 grains of Retumbo with 200gr Accubonds or between 95 and 100 gr Retumbo with 180 gr Accubonds, 180 NoslerBtips, or 178 Hornady Amax you will find something you like.
RL25 works too with smaller doses but cleaning is more of a chore.
Accubonds performance I have witnessed from 200 to 900 yards is like driving a 1" pipe through your target. Doesn't really matter what is in between. The Btips are a little more graphic in nature. The 178 Amax are accurate, I haven't used the 178 on game although I do use the 162 Amax in 7mm with good performance, about 1 1/2 inch exit hole at half mile.
I personally wouldn't use anything less than a 180 bullet in a 300 RUM. Different powder/bullet combinations will generate different pressures. Check a few reloading sources to find good starting points. It would be best to get a manual from the bullet maker and/or powder maker or give them a call. I am running 180 E-Tips out of my 300 RUM with 97.5 gr of Retumbo. With a 180 bullet I would recommend starting at about 90 gr but your best bet is to contact the bullet maker and then the powder manufacturer.
I have shot four boxes of factory ammo and had far superior accuracy out of the 150grain factory loads, seems to be a compressed load also, the 180 grain loads dont group as tight but that is factory stuff. I also have had much better accuracy out of the scirroco bullets than nosler, also factory rounds. That is why i said 150 grain bullets, all game shot with swift scirroco has been drop shots, coyotes, major damage, deer not as bad, seems to be a very good bullet....
Nephew has a 300 RUM and said the same thing about the Scirroco Bullets, he bought box of 150 gr when got rifle and had a .5" group. Bought some reloads from an individual that will not group at all 3.5" at 100 yds. Thinking about starting with 165 Gr Nosler Ballistic Tips and 94 Gr RL 22. Has anyone tried this combination?
I've been reloading 100 gr. of Retumbo with 180 Accubonds and Fed 215 primer...I haven't had a chance to shoot thru a chrony but this load shoots a 3/4" five shot group at 100 yards with my Remington 700 with Hs stock and KP barrel...Good enough for me lol. I've shot 2 deer with the load a small doe at 20 yards and an 8 point at 650 yards. The bullet doesn't expand much at 20 about the size of my thumb and at 650 about an inch exit wound. Great hunting bullet with little meat damage(on my shots...I don't know what happens if the bullet hits the bone yet). I am impressed to say the least with this load.
I have the best luck with H-1000, (at 96.0 grains now) fed 215, and Berger 168 VLD 3300 fps plus/minus 16 fps. I have shot 18 animals so far from Antelope to Elk , at up to 613 yds, bullet performance is exceptional. The hornady 165 SST shot very well, but is VERY destructive at all ranges. My experience with heavier bullets was OK, but not nearly as good as the 168 VLD. I stopped at 96. gr. as my PAC=NOR bbl'd rifle starts to show pressure signs above this, but the factory bbl would handle up to 99.8 (but only lasted 262 rounds, thanks REMINGTON!) am at 566 round count on the PAC NOR after this Elk season.