Re: 243 Rem 700 question
Ok, time for me to get up on my stump.
Buy the .243, definitely, but for yourself, not for your kid. The absolute worst thing you can do to a new hunter, kid, wife, whatever, is to saddle them with a marginal cartridge on their first hunt merely because "it kicks less." By that logic we all should use a .22 short. Ok, .22 CB cap.
Wrong. Way better to give them a slightly heavier gun in a way more adequate caliber. You want their first deer to go down in a pile without a twitch, not flop, squirm, and scream for 20 minutes, otherwise you're taking a big risk on turning them off hunting, or even to anti-hunting, the very first time out.
I'd suggest a 7mm-08. Works _good_, makes deer flat without kicking too much. .270 or .260 if that's what you've got. Even the .25s, which I love, are not wise choices for beginners.
Buy that .243 though ... for yourself. Or use the action to build that 7mm-08.
Flex is for people who don't have lockers.