My son killed his first one last year when he was 7 with a heavy suppressed 308 but was using a tripod in a stand. This year I switched him over to a shortened 308 BLR that I used when I was his age. Recoil has not been an issue for him, but he has never shot the lighter recoiling calibers to...
I load mine to 3.500 to feed out of the magazine of my Savage and they shoot great. I don't remember how far off the lands this is but that was the max I could easily feed out of the magazine.
I could not get H1000 to shoot well in mine with the 180 ttsx, but I have had great results (1/2"@100) with 74 grains of H4831SC. I load to 3.500" and they feed out of the magazine on my Savage with a Sinarms barrel.