I've never had a problem using a 243. Try 85gr Sierra HP boat tails and 60% of a max load of H4895 or IMR4895. I've loaded youth 243 loads for friends and their children never had a problem dropping a deer.
For a 7mm-08 youth load I'd use the Hornady 120gr FTX and 60% of a max load of IMR or H 4895.

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