Fatboy,
Got onto this thread a little late but have read through it with great interest. Have had a lot to do with the 284 since i first chambered one up 15 years ago. The tale you tell is all to familiar as just recently a fellow over here had a duplication of your nightmare with a 8.5 twist barrel and all the same pills and powders you are using or thinking of using. Heres the two cents worth i gave him. The faster the 175/180 are driven the worse the groups got so i advised him to slow right down using the H4350. It worked fine but was a waste of cartridge and bullets as they/it were not used to their full potential. The next thing i told him to do was to get a 9.5 twist barrel which he has done and in his first match he came a creditable third using the 175 SMK at just over 2900 fps. The one thing i did say to him which he did not get to try but i know from my own experiences is that when all else fails go to the 168 SMK or better still the 162 Amax which should never be discounted and run 51.5/52 grains of H4350 with either. Both of these pills can be shot through a broad range of twist rates without major loss in accuracy. One thing i know for certain is that some barrels with fast twist rates like 8.5 make the 175 SMK do some very strange things in the vertical plane. I have shot them in 9, 9.5, 10 and 11 twist rates and the best is 9.5 at a speed of 2950 fps in a 280 AI and the 10 twist in a 7/300 Magnum at 3200 fps. As far as the 180 Bergers go i have only seen them play the game in 9 twist or faster and because of their vertical tendency i would only shoot them in F Classs where a slightly larger group doesn't matter too much. In 1000 IBS these pills were real crap and the 162 Amax,lot 326) made them look like junk. 4831 SC in the 284 worked fine for me in the region of 57.5 grains in the old Winchester brass, a load that will probably lock up the bolt with the Lapua crap, but if you experience large variations in humidity it will let you down as the barrel will powder foul badly as the humidity goes beyond 80%. Best of luck with anything slower as i have been there and have yet to find anything better than the 4350 that you are using.
Tony Z.
ps. I would bypass the 4831 SC completely and go to H4831. Both are made in Australia by ADI but they are completely different. I have been using this powder for a little while now and the speed gained and the lower pressures with the H4831 would indicate to me that it would be a better choice than the Short Cut stuff. The jury is still out though on whether it powder fouls like the SC cousin. The ADI manual lists 53.5 grains of 2209,H4350) and a 168 grain pill as a maximum load,2822 fps in a 24" barrel) and 51.5 grains of the same with the 175 grainers,2649 fps) . I garantee that these loads are a surefire way to keep you busy replacing Lapua cases after a few firings as my experiences indicate that the brass heads are soft and the primer pockets swell at relatively low pressures. Hope your brass is better.