I’ll disclaim right now this load is not published for use but for my own education and that of others, from those more knowledgeable than I, if you use it then it is at your own risk, I will not be held liable for any accidental loss of life or limb.
I recently procured an 16” ar15 upper with a pistol length gas system and a strike industries adjustable gas block chambered in 300blk. After playing with jacketed and being unsatisfied with the pressure/velocity/energy/accuracy results at near max loadings with 150grainers I decided this was a perfect candidate for cast bullets. I started out with the lee 180gr round nose sized .309 and after playing with the alloy and lube, which started out as Felix lube and water quenched wheel weights from a previous project, has transitioned to carnauba red and 50/50 Linotype/wheel weights and a touch of tin air cooled. The end result was a load of 17.5grs h110 (note 18grs shows pressure signs) cci450 primer, full crimped at the groove and a bullet weighing 165-166grs checked and lubed going at a velocity of 2034fps into a .432” 3 shot group at 50yards. At 25 yards i expansion tested the bullet in 5 2.5gal agricultural chemical jugs filled with water. The bullet penetrated 4 and expanded to .41” and the retained mass was 97grs The only problem with this load for hog and deer depredation is the fact the bullet can’t be seated far enough out to fill the mag due to a tight throated chamber and so it jams now and again in the chamber at about 45 degrees. Now the criteria that I’m looking for is a 160-180gr bullet traveling at circa 2000fps, that is fairly accurate and with a moderate expansion and does not jam. I have since switched to the noe 311-195-rf-j1 made for the k31 and have begun pressure sign testing. Even though it weights 20grs more at 186actual then the 180lee, the max charge still appears to be 18grs at a velocity of 1987fps, based on primer dimple and ejector mark. The question I have is this; how close am I to a max charge or am I dangerously over the line? I have failed to date to find published cast load data on this particular cartridge and charge/bullet weight, but perusing my Lyman 5th addition cast hand book the the cast data shows max loads of similar cartridges with much less pressure than jacketed equivalents. Am I smoking the proverbial crack pipe in trying to get this kind of performance from this cartridge and bullet weight? It’s boggling my mind that a 150gr jacketed max charge is listed at 16.7gr h110 by Sierra’s online load data, and yet with each of these lead bullets being heavier by as much as 36grs I’ve pushed the envelope to the same charge of 18grs. I suspect part of the reason for being able to milk the noe is because of having roughly a 1/3 the bearing surface of the lee, but y’all may be able to shed more light on this assumption.