I've never had bullet set-back in my Luger, even with cannelure-less, uncrimped bullets.
Were you using .308" bullets? I've used .309s, and .311/.312 run through a .309" sizer.
Rick, I tried several...Speer plinkers, .30 caliber carbine fmj's, and 93 gr Remington FMJ's specifically manuf. for .30 Luger. None wanted to stay in the case as seated.
My groove dia. on the DWM Luger measured 0.310" so that's what I sized my Lyman cast bullets at. WW alloy air cooled did not group well at all, nor did quenched.
I did have good success with Hornady .32 cal. swaged LSWC's, crimping into the soft lead, as well as early versions of the ~100 gr & 85 gr XTP, and also with the Speer & Sierra versions of the preceding. All of these jacketed bullets had a cannelure which facilitated crimping and that stopped the telescoping problem. Accuracy with all of these was well below 2" at 25 yds from a rest...and that's saying a lot considering the Luger's barley corn front sight and V-notch rear, not to mention the rubber band feel of the trigger when it broke (a precursor of the famous or infamous Glock rubber band 'feel').
Powders: Win 231, Bullseye & Unique in about that order of usefulness at mid-levels from Lyman Loading manuals worked well. Velocities in the 1150-1200 fps range with good/excellent accuracy.
It was and is a fun gun to shoot, accurate from a rest, but flips its brass 7-ways from Sunday on ejection. Over 20 years ago, Midway got rid of their 93 gr .30 cal. Luger bullets at a couple cents a piece...I bought 'em all, nearly 2000, figuring I could eventually come to a loading method to prevent telescoping. I did, and it was the use of a "CH" brand canneluring tool.
With it, I was able to manually groove any bullet I wanted and also to adjust the cannelure height where it was needed. Voila....problem solved.
It's been many years since I've loaded for the old Luger, & still have several boxes of super accurate ammunition for it; both factory and home made, that I haul out when someone wants to see what a "real" Luger shoots like. We spread a poncho, and find most of the spent brass, and everyone marvels at the precision machining and beautifully contoured grip design...but no-one, and I mean no-one ever went so far as to buy one and try loading for it.
Best regards, Rod