Limiting the number of members in a private range when the number exceeds the possibilities of the range itself sounds a sensible proposition.
However, from what you posted, the "inconsiderate" members are already on board.
I would suggest to take, as a first step, a survey of the usage of the range by the different members (provided you keep a record). There may be different categories of members or particular sessions for hunters to zero their sights.
Rather than having existing members to second the joining request of new members you may consider to have a probation time when the new member can attend the range only when a "wise old" member can check them.
Just my two cents....