Well if you look at the ft.lbs of energy, 9mm and .45ACP are very close with .45ACP giving a slight edge. .45 ACP costs more to shoot has lower penitrating ability (350ft/lbs over 9mm diameter or 12.5mm, 9mm wins the penitrating according to maths).
9mm gives you more ammunition per magazine and per kilogram than .45acp. I strongly suggest 9mm first then move onto .45ACP. Also, ditch the Beretta and get a Sig P226!
9mm gives you more ammunition per magazine and per kilogram than .45acp. I strongly suggest 9mm first then move onto .45ACP. Also, ditch the Beretta and get a Sig P226!