Why dirty a perfectly good gin?Probably not really.
Gin is about 80 proof. And you'd add what, maybe about 1 oz to a 16 oz budweiser that's 10 proof.
So, realistically you take 40 units plus another 80 units then divide by 17 ounces total volume. That's a 14 proof / 7%abv drink overall.
Of course, you probably want to drink lots of other things prior to having any budweiser, ever, so that's a whole different story