GH
If you ask 10 diffrent loaders you may get 10 diffrent answers , personally I feel that its a CYA thing for Lee , as the Fed primers tend to use a slightly thinner cup Lee may be afraid that if you pop a primer in their Auto Prime and get hurt , with out the warning they may take the heat for it .
Others will say its because Richard Lee had a falling out with Fed many years ago , I have used 10s of 1000s of Fed primers in my Auto Primes and never had one pop .
stimpy