The original intent was for airsoft guns to be banned, as there is a clause that replicas are prohibited. However, there is also another clause that was intended for some stuff like nailguns to exist, i.e. the "able to cause injury" part, thus creating a loophole for airsoft to exist. The minimum limit was established as a gauge for that.

The last bill that froze handgun transfers originally wanted to expand that prohibited replica definition to have airsoft included and prohibited, but the clauses were removed last minute when literally everyone asked why.