I wouldn't waste my time with the Scirrocos. I have shot them thru three 300RUM, same box, and all grouped about 2.5". I also tried reloading, and quit. They build pressure quick. Also, I know you got ya a nice little load there, but Remington doesn't make the 180gr nosler partition anymore. Goning to have to shoot 180g Corloks. If I was you, I would call and complain a bit. If you want to match that 180gr partiton, put 94.5gr of H1000 behind it with a 9.5 primer. Load her to 3.57". And she will be a spitting image of the factory.

Congrats and welcome to the 300 Ultra club! I'm shooting the SS 700 and had a brake installed. Cut the recoil in half and makes shooting at the range enjoyable (At least for me, haha). (Take the brake off hunting). I haven't had the luck you've had with the factory loads. Can't find anything that'll group great like yours seems to. I have worked up a couple loads using the new Nosler Accubond in 180gr and Sierra 165gr HPBT Gameking. The 165's will cut a jagged hold off the bench. What I have discovered in my rifle is, it really doesn't like the hot loads and does much better on the low end of the scale. Can't explain it, but I've proven it with every load/bullet I've loaded. Happy Shooting!

There is a good article in handloader mag that might explain your results with lower pressure loads. They showed a graph of pressure over time. It showed that peak pressure might occur at the chamber, but thier was also a pressure spike as the bullet was at the muzzle. With max loads, that spike seemed erratic, but at lower pressures, that spike was more reproduceable and more stable.

If you look at alot of the load data people are saying on alot of pages, they are saying they get .5" groups at max loads. I have loaded up three of these RUM, and I almost always get best results at middle range loads like 94gr of H1000 for a 180gr partition, or 88gr of Re25 with 180 tripleshock.

i have 300 rum in remington bdl it kicks but is great