Lots of ranges have restrictions for SKS or surplus ammo. The reasons behind it is because of a few bad apples ruining it for the rest of us. Cheap surplus ammo and a couple of yahoos seem to shoot up the place and leave a big mess behind. I'm not suggesting that this is fair, but its a knee jerk reaction by shooting ranges to curb the damage and inappropriate shooting behavior of a small percentage of individuals. At teh end of the day, you have to consider that the range takes responsibility for the actions of its members, and could consequently have the range shut down due to the actions of individuals who break the rules.
Its unfortunate, but cheap ammunition combined with troublemakers is the cause of the problem. Ranges across Canada are trying to deal with this, some with reasonable solutions, and some with very poor ones.