Private seller is a thing, it is someone who is privately selling a firearm they legally own and no longer want. Not considered a straw purchase. Purchasing a handgun from a private owner is legal as long as you're 18 years old Shockwave is a pistol under a classification, go to academy sports website and look at the shock wave, it'll state you cannot buy until 21 because it's classified as a pistol, same as a 12" barrel AR15 Shotguns are considered rifles when purchases are made, therefore you can buy rifle ammo at 18 years old (5.56 7.62 12 Guage 6.5 Creedmoor ect.) Where as 9mm 45acp 40 cal are all considered handgun rounds, which is why it is relevant because the Shockwave is considered a pistol but the ammo is considered rifle ammo.