Ahhh why not just fire form 280 Remington in the chamber?

If the AI chamber is reamed correctly then this works a treat:-

Standard Remington core lockt in 280 Rem on left and fire formed with Remington 175 gran bullet seated into case on right. That was the first case fired in the new chamber.

I reamed the chamber as per Ackley's hand book 0.004" short to provide a slight crush fit with factory ammunition. The barrel was factory one for a BSA CF2 in 7x64 new in the white. My rifle is a BSA 1st Pattern Monarch the tenon on the barrel required a bit of altering to fit as I didn't realise that the CF2 had a slightly different tenon. Chose the CF2 barrel as it has a larger profile at the chamber to the rather slim Majestic/Monarch barrel profle.