I don't like loading at the range, so I use a plan like RSW suggests. Before I got a bunch of rubber plugs at work before I retired I used white styrofoam squares cut to a little bigger than the case. They would sort of form fit into the case leaving abouthalf the size of the block sticking up. They then offered a handle to pull the thing out and off the case mouth. Most of them would die in the trip to the range and back, but it was easy to make new. 
This would offer a chance to shoot a little until you lay in a supply of reusable stoppers.