Daryl, I have both of those books, and have always been a fan of P.O. Akley, and his so-called improved cartridges. As you say his cases did reduce reverse thrust of the case on the breech face. This also gave more speed without increasing chamber pressures beyond limits of the rifle. He also realized that most rifles could stand a lot more pressure with the improved case than with the standard case.

In the rifles he worked with they all had very strong extractor power, so the cases, though they gripped the chamber walls better the extractors were up to the task. This is where the AI cases or any straight case high pressure cartridge have a problem in the double rifle. The double rifle depends on the case shape to make the extractors work at their best. They depend on the low pressure to reduce reverse thrust, and the taper in the case to make extraction/ejection easier. The tapered case has only to move a couple of thousands of an inch to be completely free of the chamber walls. This works because the first couple of thousands of the extractor movement is the place where the extractor has the most power. With the tapered case the case is free of the chamber walls by the time the ejectors are hammered not hindering extraction, or ejection.

The actions are made to stand factory pressures of the cartridge the factory chambers the double for. However, if that pressure is in a flanged case the extractor has a very large surface with which to start that high pressure case out of the chamber, or double with both barrels being extracted. With a rimless/belted rimless cartridge the extractors are tiny spring loaded pawls that are nowhere near as strong as the extractor for a flanged case. This is then a compounded power/strength/case shape problem that, IMO, will sooner or later show its ugly head. I predict it will happen when it is least wanted!

IMO the off face condition in double rifle is caused more by poor care and lubrication of the lock-up mating surfaces than chamber pressure! The old tapered low pressure cartridges that were designed for double rifles will always be the best choice IMO!
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