Dan and all, here's a bit more detail.
The rifles and page numbers you list from MGII show that the two Oerter rifles that were taken to Germany or England ca 1776, and both observed by gentlemen from across the Pond are the straight bored examples, while all the other Oerter and unsigned rifles remaining here are relieved. I have handled most of those in this country, and relied on others in some cases. This split response is interesting. Perhaps the English reviewers looked in a different way, the barrels are in fact relieved with the rifling refiled, and not obvious? I tried to explain what we were looking for, but cannot say for sure.
Those two Oerter long guns were probably taken or surrendered soon after they were made, and have been preserved with little shooting or wear - they remain in almost new condition. All these that I have seen are relieved round, even and I don't believe result from ramrod wear at the muzzle. On these and many later rifles it appears that the muzzle was reamed 1 to 2 inches deep until the rifling at the muzzle or up to 1/2" below the muzzle was removed, then rifling was refiled at the muzzle - for decoration? This filing is often exaggerated and of a different form than the rifling grooves, sometimes with rings, dots or stars added on the muzzle face. Rifles #43 and #52 in Shumway's RCA Vol I were rifled, were relieved at the muzzle this way but the rifling was not filed back, and without good light George thought both were smooth rifles. The same may be true of others in his books, and the old KRA gunroom in Carlisle where he photographed and measured most rifles was notoriously dark! Herb shows something similar in his recent Hawken post. Jack Brooks showed this to me many years ago, and this is generally how we finish a rifle unless the owner prefers something different.
That's the info we have noted. The relieving or funneling, often with rifling filed back at the muzzle and a flat face without modern crown are there. Now we can argue who, how and when this came about. Bob