On the WW2 "L" drum this is; .536 + .001, the same distance measured on the Colt "C" drum is; .525 + .005, the same distance measured on the new A/O, West Hurley "C" drum is; .588.

This is .063 more distance than should be there. This would cause the top of the drum to scrape against the bottom of the receiver, as I had previously experienced with my 28 A1 Thompson in Oregon.

The next measurement is where the Body and Cover "slide plates" are located, in relation to one another. These measurements are related to the measurements above.

Your irregular position of the "slide plates" on the new A/0, West Hurley "C" drum causes the drum to hang at an angle in the Thompson magazine well. It does not hang straight down. The bottom is pulled aft.

As you can see by the sketch below, the original 1921 Colt drum magazine corresponds to the Colt receiver.

The third critical measurement is the drum feed lips. The distance between the feed lips on the original Colt "C" drum magazine measure; .383 +.003. The same distance on the feed lips on the new AO, West Hurley "C" drum measure; .405.