Double -
I have no experience with the gun or the bullet. But you always want to know where you stand with new bullets. So take a new bullet and push it into a fired case. You'll see it's sort of a slip fit. Set the OAL way out past max and then slide the test cartridge into your naked barrel's chamber. Push the primer end of the case until the case mouth bottoms out on the end of the chamber. If the bullet hits anything it will get seated deeper into the case. Carefully remove that test cartridge and record the length. Do that several times until you come up with the same number. Subtract about .020" from that measurement and you'll have the max OAL for that bullet in that barrel.
Now pretend the OAL turns out to be 1.155". Being close to the rifling, 1.155" is going to give you your best slow fire accuracy. But if you want to fire 200 per in competitions, then maybe you might want to aim for 1.145" knowing that the OAL can wander by .010" without causing safety issues. Or maybe you want to load 5 @ 1.155", 5 @ 1.145", 5 @ 1.135", etc and fire those in a ladder sequence until you get a desired velocity or clean burning load.
There's just a lot of ways you can use the max COL information.