FredC wrote on Sep 29^th, 2019 at 2:08pm:

. . . could you clarify the up to .016 clearance tested with shims , which gauge are you suggesting doing this with?. . .

I am not suggesting shimming a gauge but rather a sample of the cartridges he intends to fire. The logic here is that the resultant measurement will indicate the actual amount of end-play that will be present on firing. Since it is this play that leads to case stretching and possible separation, knowing this detail is more practical than what we learn from a limited set of gauges.

Since the SAAMI spec for the .30-40 rim ranges from .054" to .064", knowing end-play with the specific cartridges we're planning to fire is really more important than the fit of standard gauges, at least to the individual firing those cartridges. (Gauge fit is, of course, important to folks fitting new barrels as well as those inspecting multiple rifles that will be fired with a variety of cartridges. It's just not as helpful when we get down to the individual level.)

In my experience with the .30-40 and cartridges of similar size, end-play/stretch less than .020" is unlikely to cause separation on initial firing with good, modern, new cases. The recommendation of caution at .016" reflects a conservative approach.

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