Awesome cartridge. I also have one on a Lilja barrel. I load RL22 with the 140 grain Barnes XLC bullet.
For fireforming, you can also do fast pistol powder with cream of wheat and make your blank fireforming loads. I have done some with that method and they turn out good.
I bought formed brass for it from Quality Cartridge. Mine is blank headstamped, but I hear they have the correct headstamps available now. They do require you to send in fired brass, because there is no real "standard" in these Ackley cartridges. You might have to play with your size die a bit as well, but that usually isn't too much of a problem.

yep,..RL22 and 4831SC love the 140-150gr in that case. I Adore my 280AI,....nothin quite like it.

I have a Lilja barrel going on a blueprinted Rem 700. That is what I thought. I just wanted to make sure. Thanks for the info.

Hornetfan - I have a 280 Ackley. Great cartridge. If your chamber is cut for a crush fit with standard 280 brass there's no need to jam the bullet or do anything out of the ordinary. The crush fit will take care of headspacing. Load the ammo like you would ordinarily do with whatever bullet/powder/primer combination you want. Use only a high end load because the pressure will be automatically reduced when firing in the improved chamber. Velocity will also be somewhat less than the same load in a 280 Rem. Fired cases will be about .015 to .020 shorter so don't trim until after they're fireformed. Accuracy should be as good as the barrel you're using. Good Luck

Ray

I will have my new 280IMp in hand in about 2 weeks. I ordered the reamer so I will have a slight crush on the parent case. I was going to jam a 140 Accubond and load about 1 grain under listed max charge of H4831 for the parent to fireform. I will not be able to get a whole lot of load devlopment done so I was going to hunt with it like it is this year. I did not want to buy high speed powders to fireform 100 pieces of brass. Will this work? Or should I use the IMR7828 heavy bullet combo?