Old thread, but a good one. I wanted to add to this one as it pertains to what we are working on.
We just got a customer rifle done and started doing load development. It is a 300 Norma mag improved. Rifle is Defiance Deviant action, Proof carbon fiber Sendero contour at 26", medium Pain Killer brake, Jewel trigger, AG Composite sporter stock, topped with Nightforce SHV 5-20X56. The improvement picked up about 6.5g in powder capacity. We got about 1/2 of the brass fire formed and just couldn't wait to work loads, so we stopped forming and went to loading. The Proof barrel is a 9.4" twist so we designed a 200g Hammer Hunter for it. We also HBN coated them.
Started load work up with RL-26 but stopped after a few rounds as it was looking like we would not be able to get enough load density with it. We then tried RL-33 and ran out of case capacity and barrel length to get to pressure. Next on the list was H1000. This turned out to be the ticket. We reached about 98% load density, just under compressing, at 90g and 3250fps. At this point the load was just starting to show some pressure with slightly flattened primer. If it were our rifle and it was staying here we probably would have taken it higher to see top end, but there was no point as this rifle will be living in Missouri. We backed down a grain to 89g for a vel of 3215fps and single digit sd's. Very happy with this cartridge and load. Shooting RUM velocities with 10g less powder and a significantly shorter cartridge. Fits nicely in standard magazine with bullets seated out long enough to stay out of the powder column.
Rifle looks like a very good shooter. So far only shot at the short 200 yard range. All of the load development fell inside 3" and the final load was shooting inside 1". This rifle is at 10.5lb and very comfortable recoil wise. About like .243.
This is a pic of fire forming before and after.