Violations of the NFA are punishable by 10 years in prison, forfeiture of all devices or firearms in violation, and the individuals right to own or possess additional firearms in the future. In addition, there is a penalty of $10,000 for each of certain violations.
In addition, a willful attempt to evade or defeat a tax imposed by the National Firearms Act is also a felony which is punishable by up to 5 years in Jail and a $100,000 fine under the tax evasion statutes. This penalty could be increased to $250,000 for individuals and $500,000 for corporations.
This means you could be looking at a maximum of 15 years in Jail and $510,000 in penalties for a violation. Many violations can be avoided by proper ownership and knowing who can be in possession and use the Title 2 firearms which are restricted under the NFA.