Josh,
At his age, with his size, and with his inexperience & lack of personalized on-site instruction, I'm emphasizing eliminating as many variables as possible and learning with the most stable & easy-to-hold-the-gun-still position possible.
Part of his lack of success until more recently has been that he had no real idea where his guns were zeroed, and not enough experience to be able to determine whether his inability to hit where he wanted consistently was because of him or because of his equipment.
Learning the basics in as easy a shooting position as possible will help him get to the point where he can have enough foundation & knowledge to both adequately zero his guns, and then to determine if the problem is him or them.
Shooting prone, especially with his .30-caliber steel-butted heavy military surplus rifles, will not be as efficient in working through that process.
He'd have the support issue, the weight issue, and the unpleasant recoil issue as diversions.
Those are lessened, to a degree, in a fully supported bench position.
Even with the .22, easier to focus on trigger & sights at the bench, when everything (including Mo) is fully supported.
After weeks of trying to get him to settle down & quit ping-ponging around with different guns, different distances, different positions, and different targets, last week he did settle down & follow the program, and for the first time we saw clearly definable & analytical progress, with his .22, off the bench.
Doing what I've been trying to get him to do, we now know that he CAN manage the basics, he CAN produce acceptable groups at 50 yards off the bench, he CAN put them where he wants them, and we CAN determine where that gun is zeroed.
With all the data that he's provided, we can clearly see measurable progress, at last.
That progress can be applied to improve his skill level with that gun, and it can be transferred later to his larger rifles.
The continual emphasis I place on removing variables, standardizing on the bench at one distance with one target & the same ammunition & hold is to let Mo see what works & build a foundation he can use elsewhere.
One he learns to shoot, I don't care what, where, or how he shoots.
That'll be up to him.
Denis