I started shooting an -06 with 180's when I was 13, & it kicks harder than my 270WSM loaded Hot with 140Accubonds.
The 243 is a cool round. But not even in the same league as the 270win, or WSM.
I'm sure the 243 would knock a deer on its butt, but the 270 will do the same thing quite a ways further out, plus can be used as an Elk rifle if she ever needed one. It's a bit more versatile is all.
Of course you never even mentioned Elk, so, the good news is you can't go wrong with either.
Guess you better buy both. Haha.
Id second bigngreen's advise for recoil reduction, & run with the 270WSM, but that's me.
My boys will start out with either 300WSM or 270WSM, loaded light,or standard -06 or 270win cause Elk are on the menue where we hunt, & bears are a regular occurance as well.
Best of luck with your choice, & with your lil huntin buddy
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