I don't know if it's possible, but I read somewhere that you can give Boone a different weapon to use.

I got a new Sniper Rifle and traded it to him, but he still uses his old school Hunting Rifle looking gun. Is there a way to make him use the Sniper Rifle?

Thanks

Is the sniper rifle fully repaired or mostly damaged? Did you give him some .308 ammo to go with it?

You have to give him ammo, too.

No I didnt give him ammo, that's why. Makes sense.

Do I have to keep him stocked up on ammo? Or does he keep it unlimited?

All companions only have unlimited ammo for their default guns. So, yes.

He needs to be kept stocked on ammo for any weapon that's not his default.

Yes.
I gave Boone a minigun once (!) and he roasted his way through 400 precious ammo in minutes, then went back to his gun.
Apparently there's a problem with modified weapons though - just give companions default stock weapons.
I gave Veronica a double-modded 5.56mm weapon and she wouldn't touch it, apparently that's normal.
Regards

That's more because she doesn't have the skill to use high level weapons.

My Lily was using a fully modded minigun. And I know many people who have their Boone use a silenced Sniper Rifle.

Awesome, Thanks for the help guys.

I've tried to play through the game without looking at a single guide, without watching any videos, or anything. I have to say, after ~40 hours, I've had a blast. It doesn't beat the classic FO3, but turned out to be a great game. Props to Beth/Obsidian. Can't wait for the DLC

I gave him the marksman carbine with armor piercing bullets and hes a BEAST wit it.

He also has on t-45b power armor and a ranger combat helmet on.