[aaronraad]

After reviewing cartridges I always thought the best case to start with a subsonic .510 calibre project was one of the old rimless cartridges like the 12.5 x 70mm Schuler/500 Jeffery Rimless. The idea being trimming these back to length, and setting the shoulders back to allow a 30/06 bolt action to load. That way you could save the cost of an expensive magnum action or opening up the boltface and spend more of your money on reamers, barrels and cases which you'll have to do anyway.

I don't think a Winchester 284 case is big enough to expand to .510 but it might be an interesting project for the new 25 WSSM case. I believe the brass in the WSSM range is extremely strong for the high pressure loading. Now what about the 50 AE Desert Eagle round loaded in a bolt action with a 750 gn Hornay A-Max to subsonic levels, surely that would make a light all day walking rifle? The only thing is you really want on sholder on the case to headspace on. I must be due to win the Lottery.