I'm with Dillonbuck:
"If I was building one, from scratch with no dies, or brass or loads…. I’d AI and fast twist it. Otherwise, I'd let it go."
If you already have dies, enjoy what you have and appreciate spending that extra $150-200 on powder, primers and bullets as you happily go forth and slay beasts. The improvement in the 25-06 AI compared to the factory chambering (at the same pressure level) is minimal, according to P O himself, and making it more overbore limits your powder selection. The reference I found, besides P O A, says a 100g load can go 8.4% faster in the AI version; that puts it 10th on the scale, behind the old tapered cartridges (25-35 WCF, 30-40 Krag, 250 Savage, 6.5 X 55 Swede, 30-30,7 X 57, 30 H & H, etc.). Much the same increase in velocity can be obtained by using longer barrels or boosting the pressure to unknown/unsafe levels, which is much more difficult to measure than velocity for us amateurs in the field.
That said, I did build a 280 AI from parts and I don't regret it, but it still isn't a 7mmRM when the chronograph whispers to my wallet. And a 257 Bob AI from 1970, before we really knew that the 25-06 was gonna fly.
