You could take the FLS die down a fraction and I do mean a fraction of and inch say 1or 2 thou just enough so it will act like a body die to bump the shoulder down a fraction as thats all it needs or get a body die and set it up its a bit painful I use them on my 308 and 6.5 x 284 so I get the same consitent resistance to the bolt closing on every round. But be wary with the FLS die to far down and you'll munt the cases myself having never done that a few times!
Apart from that as Jim suggests slow as you go with his suggestion.