I have only fooled with about half a dozen "improved" cases, and all required little or no trimming at all, especially when compared to the parent cases. My guess is that the steeper shoulder does inhibit the flow of brass somewhat, but also PRECISELY headspaces the case in the chamber, thus preventing brass common among some rounds.

I know that I NEVER had to trim brass in my .257 Roberts AI, and do every 3-4 firings in standard Roberts rifles, even if the brass is only neck-sized. Also, I have yet to trim .280 AI brass, even when it is new from the factory Nosler stuff.

By the way, the .300 and .375 Weatherby rounds act just like AI rounds, preventing much stretch, especially when compared to the .300 and .375 H&H rounds they're based on.

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