I don't understand the fascination with the 300 Blackout in a bolt gun. I barely understand the fascination in the AR platform. Guys get all creamy over it but to me it's got nothing really going for it other than being able to drive a 208 AMax about as fast as a fart.
I know that you handload. I'd just get a light weight 308 and download it to wimpy levels with a lightweight bullet and GD3 will thank you for a rifle that will actually last and be relevant as she goes through her hunting career.
Do you own a .30-30 Winchester? Would you see a use for that? The .300 Blackout, 7.62x39mm, .30.30 Win., and possibly the ancient .32-20 all have comparable ballistics.
Nobody is going to try to change your preferences because you already have your mind made up. The Blackout isn't for you and that's ok. No one said you had to like it. It definitely isn't for everyone.
There's no argument that a .308 Win. would be a great choice in a bolt gun. However, life would get pretty boring if we were all left with just one choice, right? You can make the same argument for .223 vs. .22-250 in a bolt gun. Why have a .223 when the .22-250 does everything the smaller cartridge does and with higher velocities?
The .300 Blackout's strengths lies in its versatility with all .30 cal. bullet weights ranging from 90gr.-250gr. at subsonic and mid-range supersonic velocities while using a short barrel length. This is an area where the .308 Win. does not excel in and is easily surpassed by the smaller more efficient cartridge.
Lighter weight .30 cal. hunting bullets can be found in all brands. One of the best commonly found bullets for deer sized game is the Nosler 125 gr. BT. Barnes makes great premium bullets that are among the best. The Barnes TAC-TX FB #30811 bullet is designed to expand at lower velocities and has great weight retention after expansion.
With deer saized game, penetration is not an issue. You simply don't need much to get the job done. Even a .22RF will suffice if the right ammunition is used and proper shot placement is made.
This isn't my pic but one that best illustrates the point.