Cam Cooke, the simple thing would be a barrel for each as I stated over on the other site. This based on the fact you still want the use of the 10mm cartridge as well.
You could do a test by shooting a 40S&W from the barrel to investigate if the therory works like you invisioned. But you may see where bullet material will shave off as the round passes the end of the chamber...if that happens it would distroy the accuracy of the shorter rounds in the longer chamber if you follow what I am saying!
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