I built a 375 Whelen AI. The feed ramps and the lips of the magazine on the Mauser needed modification. (I hate relying on me to be doing modification on things like the feed ramp and the magazine lips.) Amazingly enough, it now feeds both a standard 35 Whelen expanded to 375 and an AI version. I would not have done that but for a couple of reasons.
The reamer and dies were available in the AI version. There was a long wait for 375 Whelen and 375 Brown Whelen reamer and dies otherwise. I was worried about the shoulder, but that would may not have been an issue as I maybe the 375 Whelen and the 400 Whelen have wider shoulders than the 35 Whelen. (I'm going from memory here, maybe it's just the 400 Whelen with a wider shoulder).
The second reason is what every one who likes AI says: "The stretching is minimized."
The third reason, is when I take out my Mauser 375 Whelen AI no one else in camp will have one.
On the other hand I have a 280 AI that I put together on a 700 action and there was no need for modification as it fed 280 and 280 AI fine. (If I had to do it over again it would be a straight 280.)
The same things on my 22-250 AI built on a 700 action, except the 22-250 AI does show enhanced performance and I think it is worth it. Basically a 220 Swift performance in a case that doesn't stretch much. I shoot maybe 200 rounds a year in my 22-250 AI.
If I were to build a 338-06, I'd go with the A-Square version.
I think MD wrote once that controlled feed actions might require more modification than push feed and that's my experience.
