I have done two of them: 280AI and 223AI. Besides the novelty of it and the possibly extended brass life they really aren't worth it. The Remington 7MM SAUM exactly duplicates the ballistics of the 280AI with a factory (albeit nearly extinct) round. When pressure is kept to a reasonable level the velocity gain of the 223AI hardly justifies the expense. Fred at SSS told me the 223AI wasn't worth it but I didn't listen. I had fun building them and enjoy shooting them but I probably wouldn't do it over.
Charlie