Have never heard of an underwater assault rifle. In the US, you must be 18 to buy a rifle, and 21 to buy a fully automatic rifle.
A TRUE Assault Rifle is fully automatic. Federal law requires you be 21 to buy one of those in ANY state. However, what people may CALL an assault rifle (such as a semi-auto AK47) can be purchased at 18.
18.
Wal-mart
100-1000 usd
You can buy a semi automatic Title I rifle at 18. To purchase a true, select fire (auto or burst) NFA tax stamped assault rifle, you must be 21.
The most expensive.
a full automatic rifle
Only the fully automatic firearms that were already registered with the BATFE by May 1986 can be transferred to a private citizen. Which is why the price of a LEGAL, papered M16 that can be transferred is about $26,000. Since the supply is finite, prices have risen sharply.
You upgrade the first sniper rifle to the maximum. And you have to have completed the storyline.
18 for a military style semi automatic. For a true assault rifle, which would be an NFA Class III full auto weapon, 21.
Yes, you can ship semi automatic bb guns to new zealand but not fully automatic ones