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I picked up 5 boxes a few months ago because I thought it was aluminium case ammo. I realized that it is metal case latter when I wanted to shoot it. I checked a few forums and most users say it does not really cause any damage to the gun but it is not really recommended because it might cause excessive wear on the feed ramp. Some steel case ammo might also cause excessive wear on the extractor. I checked how my gun feeds it by manually moving the slide and it looked ok. As I lost the receipt and I could not trade it back for the more expensive brass version I am slowly using it up by putting a steel case round to the top of the mag only and use brass ammo for the rest. When I change clips I manually drive the slide back so there's no excessive force to push the case against the feed ramp. I did not notice any extra wear so far using it that way.
However I am not planning to buy that ammo any more, the $1 difference is not worth risking any damage to your precisuos tool.