Most FL die sets have a crimper built into the seating die but you don't need to crimp for the AR-15. Some die sets have a separate crimp die. You may want to take another look at the instructions that came with the die set.
Check the overall length of your rounds and make sure they will fit into all of your magazines. Usually the overall length should be between 2.250 to 2.260 . That 24.0 grains of Benchmark will likely shoot very well. Stay away from magnum primers with Benchmark. The CCI-BR-4 would be my first choice of primer but others should be fine as well.
Let us know how it shoots for you.
Jim
