I've spent more time studying the loads and test firing some; I've come to the conclusion that the 300 Ham'r is really just a ballsitic reproduction of the 7.62 x 39 out of the 5.56/.223 case. The taper is straightened a bit and the neck length puts .308" at the base of the slight shoulder. Similar to the 350 legend, the options for bullets are very limited by the length of the bullet's ogive relative to the overall length of the bullet; it becomes a "tug-of-war" between the limit of magazine COL capacity, the bullet's base of ogive not disappearing down the case mouth and the shank/base of the bullet encroaching upon case capacity. If you have loaded for the legend or 7.62 x 39 I think you'll know exactly what I mean.
Looking at Hodgdon's load data it becomes pretty obvious that the faster velocity loads are based on compressed loads of either AA1680 or CFEBlk--the later of which can go pretty high in 100+% capacity fill. It also becomes obvious you need to use good SR magnum primers. Yesterday I did a test load of Barne's TSXs using a pretty compressed charge of CFEBLK ignited by my secret stash of Tula gold SR magnum primers that I had left over from before they were banned from import
. Chrono numbers did in fact tighten up significantly and a medium charge weight got me to 2,450 fps--pretty sure I can get to 2500 (but ran out of the bullets) as Wilson claims; but I think that kind of velocity is only realistic with a few bullet/powder combos.
In the process of choosing magazines I discovered that the 350 legend magazines I had been using not only cycle the cartridges just fine (not surprising since they are both long 5.56 adaptations) but can get me out to a COL of around 2.3--that helps get a few of the better ogive flatbase bullets like berger's 115 gr seated without the base of ogive getting swallowed down the case neck. Since I spent a lot of money on the barrel and gas components I will continuing experimenting.