Konrad, are your Lugers 9mm or .30 cal.? If they are 9mm try the Winchester 100-round bulk-pack (i.e., cheap!) boxes from WalMart. I shoot them in four different Lugers, and in the last 1500 rounds or so have had maybe three or four malfunctions. If they are .30 I can't offer much help, the only .30 ammunition I have found commercially is Fiocci,and it is way too underpowered to operate a Luger reliably.
Check your shooting technique. Lugers require being shot with a firm hand. Letting them fly up under recoil ("limp-wristing") releases too much of the recoil energy to your hand, and interferes with proper operation of the action.
Are you using the original magazines which came with the guns? If so, the magazine springs may have become weak or compressed, or the feed lips may have sprung out of proper alignment. Get ahold of a newly manufactured magazine--I recommend those manufactured by Mec-Gar--and see if that solves the problem. My original magazines all jam at least some of my Lugers; Mec-Gars provide me part of the reliability noted above.
Let us all know how it works out.
Good luck, and good shooting.
--Dwight
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