243 Ackley improved reloading

Redding and RCBS make dies for it. They cost a bit more than standard dies.
Improved dies may or may not work. Who made the dies? Can you call them and see?

You could also graphite a case and check to see shoulder contact.
 
You will have to measure one of the fired cases to determine which version you have. Hopefully it was chambered with a reamer that matches a set that Redding makes. I had to send five fired cases to Redding to find out they didn't make a set that would "fully" full length size my brass. Mine was a really tight chamber made with an old Cylmer reamer. I ended up with a full length set from CH4D. You should be able to use a Lee neck die for now...or any other brand neck die.
JS