I was breaking in a brand new S&W 1911 with some 8 year old reloads of mine. The third round got stuck apparently but the gun cycled. The next round chased out the first and locked the slide. I had to send it back to S&W with an apology (and $240). I pulled a couple of those rounds and the powder had clumped together. This was back when I first started reloading and was using case lube (Dillon) and I probably didn't let it dry or used too much.
I have a couple more boxes from back then that I need to take apart