[jpwright]

I think you have the perfect excuse to buy a new gun, actually. A 9 mm, so all that brass doesn't go to waste.

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If God didn't want us to own guns, why did He make the 1911?

 

[KLN]

No. Your super headspaces either on the case mouth or the semi-rim, depending on your barrel design. In either situation, 9mm brass would not headspace properly. The 9mm lacks the super's semi-rim, and the 9mm case is shorter.

 

[Walking Point]

They are in no way interchangeable. Without reviewing the case dimensions (which are totally different), right off the bat you may notice that the 9mm is a tapered case while the .38 Super is straight walled.

Whoever told you it was a good idea should be ignored in the future.

 

[Jim Watson]

No. But...
That is $300+ worth of brass with more brass and econo-ball ammo available cheap. You might find it worthwhile to buy a 9mm barrel. What make and style are your frame and magazines? I get good feeding of 9mm ball out of Metalform single stack .38 magazines. The Shooting Star I tried fed ok, too.