Tell your friend to avoid advice from that guy as much as possible. Let him know that there are virtually no differences between brands in primer performance when loading mid range 40 S&W. Since he is new, he should know that he isn't trying to max out his load (and you should remind him not to). The guy at the LGS doesn't know the difference between shotshell primers and metallic primers. Shotshell primers vary significantly between brands and when you start loading you should follow recipes to the letter including brand of primers.
He should either:
- Avoid the store altogether.
- Know exactly what he wants and not rely on the guy behind the counter for any knowledge beyond "in/out of stock", "price" and "do you want a bag for that".
The difference in pressure variations between brands of primers would not be discernible between brands of primers and shot to shot variances on a chronograph. Again since he is just plinking with mid range 40 loads, it really doesn't matter between Fed/Rem/Win/CCI.
Agree with Wrangler for a beginner. Don't substitute type of primer unless you know what you're doing and can verify the results of substitution. That's another subject.