Piercings should be carried out using fully sterile one-use needles.
PIERCING GUNS SHOULD NOT BE USED.
To quote the Association of Professional Piercers:
"It is the position of the Association of Professional Piercers that only sterile disposable equipment is suitable for body piercing, and that only materials which are certified as safe for internal implant should be placed in inside a fresh or unhealed piercing. Reusable ear piercing guns can put clients in direct contact with the blood and body fluids of previous clients."
A piercing gun often has plastic parts and so it cannot be cleaned in an autoclave sterilising system. When the studs are pierced into the ears they simply push through and move the skin to one side...being pierced by a needle removes the piece of skin where the hole is being formed.
Guns are unsafe, and unhygienic. No professional body piercing studio would use guns. Maybe a hairdressers etc. would...but they aren't body piercers are they?
i would strongly recommend that people avoid piercing guns and find a reputable professional body piercing studio using sterilised equipment and needles.
For information about Guns and Needles please see these links:
http://www.nhsdirect.nhs.uk/articles/article.aspx?articleId=422§ionId=25727
http://www.safepiercing.org/FAQ.html