Quote History Quoted:
Don't know if anyone said it or not, but the Lee FCD is NOT a substitute for properly sized
case mouths. If the bullet isn't in there tight before you use the FCD you have to find the
problem, not bandaid it with the FCD. Occasionally a die will be bad or have a bad expander
button which will cause your problem, or undersized bullets, but it sounds like you found the
problem here. Re-do em and have fun shooting.
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I agree here. Neck tension is an important factor in chamber pressure, and a crimp does not do anything like the same thing that neck tension does. A typical bottlenecked rifle sizing die sizes the case neck well below the final size, with the expander ball opening it up to a specific size - which should be a tiny bit smaller than the nominal diameter of the bullet used. For example, most sizing dies for calibers that use .308" diameter bullets have .307" (or so) expanders.
I'm not saying a Lee FCD isn't a useful tool, but like makintrax73 points out, it's not a fix for loose case necks.
Pull the rounds you "had to crimp", size them, and you'll see a huge difference. You can take the depriming pin out of your expander ball stem and just resize and expand the cases without wasting those primers or the time to redo them. Just remember to put the pin back in before you run your next batch of cases, or you'll have a very unpleasant surprise in store for you.