Just curious why Jam a bullet ? I'm not trying to stir the pot or derail the topic. Aren't the ackleys typically chambered .004- to .010" short of the parent case dimensions or chamber? Would that nor provide a crush fit? Don't get me wrong I know that there are some pretty large variations in production brass and that some may not provide a crush fit.You CAN shoot any factory round in an Ackley improved that is how you fire form brass. And it also is a good hedge if you leave your ammo home the factory ammo will shoot pretty accurate. With my 280 AI i load lowest charge of 4895 or any powder recommended for the cartridge and jam the bullet so as to support the cartridge at both ends during firing. This is the proper way to fireform brass for an Ackley. This method will get longest life from new brass usually 5-6 firings if you don't anneal. One to two more firings if you anneal.