If the LOP was too long on the youth 20 GA it will probably br too long on the rifle as well. My son uses the NEF youth .243 it's a very accurate gun and worth a look.

I don't by into he'll out grow it though ( as far as caliber) if the .243 will kill a deer when he's 10 it will still kill deer when he's 100 or passed it to his grand children.

I still carry my .243 at times ( I've a bumb shoulder and use what I feel comfortable with for the day)