[John Henry]

In the OP picture, both hulls appear to be ribbed, whereas every Gold Medal shell I have fired, literally 1000's, have been a smooth hull.

In fact, in most brands, the smooth hull was usually the premium (STS, AA, GM) where as the ribbed hull was the bargain line (Gun Club, Top Gun, etc)

When did the GM go to a ribbed hull?

 

[John Henry]

When did the GM go to a ribbed hull?

Some time in the 1970s. They were originally ribbed (same technology that is used for 1 and 2 liter plastic soda bottles). They went to a smooth hull but quickly gave up on those due to burn-offs. They then went back to the ribbed hull.

Check your barrel for burn-offs when loading the smooth GMs.

Well, I had to go and do a double take at some empty hulls. I do see that there is very minor (ribbing) on the GM hulls, but actually can hardly feel it. Feels like a smooth hull in the hand, especially when compared to the Top Gun.