Mmm...
Let me explain where my thoughts on this are.
I have an M1A. Great rifle. Great cartridge. However, there are cons as well as pros, and I'm constantly comparing tools to see if something may work better for me. I got the rifle because the 7.62x51 reliably kills targets up close and at a greater distance than other cartridges and has excellent penetrating of engine blocks/car doors, while maintaining accuracy.
The down sides are the weight of the rifle and the round, the reduced magazine capacity, and the increased cost of ammunition compared to 5.56 and 7.62x39. I also thought I might be in a much more open, mid-Western state by now or the near future, in which the strengths of the M1A at a distance would really shine. That is no longer the case - I seem to be committed to semi-rural areas near urban areas with field of views no longer than 200-300 yards, thus negating a big advantage of the M1A and putting me at a firepower disadvantage compared to a rifle with higher capacity.
Anyway, that is how I think. I don't want a 5.56, and 7.62x39 just doesn't sit well with me. I'm not sure I have a legitimate reason to justify not liking the AK, other than even at 200-300 yards there seems to be a difference in accuracy compared to 5.56 and .308.
Then, I see the .300 Blk cartridge, which seems to combine the accuracy of 5.56 with the penetration of a .30 cal rifle. As a bonus, it is amazingly quiet when suppressed, and is almost identical to 5.56 except for the suppressor and barrel used.
I've seriously considered evaluating it's POU against my M1A and, if it seems superior to my new criteria, possibly selling my rifle/ammo/mags (which altogether cost ~ $1800), and investing in a .300 Blk AR.
It's not something I'm considering lightly, but it seems warranted. Thoughts?