1. High primers, or primer, as mentioned.
2. Do the rounds seem very light? Too light a load will cause the primer to back out slightly upon firing and jam the action. Under normal circumstances,
enough pressure is generated to slam the casing back against the recoil shield and keep the primer in its pocket. Too light loads do this in most calibers, not just .45 Colt.
With a stuck high primer if bullet has successfully exited barrel, use a ramrod and tap casing in chamber to push primer back into its pocket. Often just gently forcing the cylinder to turn will also push primer just enough to clear for rotation.
One way to check for high primers is to place reloaded cartridge on a perfectly flat surface. If there's a little wobble, then primer is not seated deep enough. It's not a good idea to try and force primer in while casing is loaded. This check method should be done while priming while case is still empty.
Also, in those casings that you successfully removed but were hard to move the cylinder, did the spent primers, or live ones, have scrapes on the surfaces caused by the recoil shield?
Live primers: not seated enough
Spent primers: too light a load
Either way, my advice is to scrap those reloads since you may face the problem over and over and worse get a light loaded cartridge to leave a bullet in the barrel.
You can use a bullet puller to check some loads and see just what's inside regarding powder load, charge weight. Ask the reloader what powder he was using and what charge weight.
Last edited by UncleEd; April 17, 2013 at 09:50 PM.