It would be interesting to know what type of powder you were using? I've been reloading for over 38 years and never had a misfire until last year when I was working up a load for my 45-70. I had 3 MFs using Reloader #7 powder. The same thing happened to me. The primer went off and the bullet lodged in the barrel. Luckily we were also shooting our muzzleloaders so I used the ramrod to tap the bulllet out of my Marlin.
When I examined the powder when I got home, I noticed it had a greenish hue to it. It was the first time I used Reloader #7 and not sure what color it should be. I am use to the IMR powders which is black in color. The RL-7 went down the sink and I am now using H4198. No more problems.