Don, I would definitely do the bullet in the fired case trick first; as Daryl stated this could be the clincher & most likely culprit.
I would like to make a further suggestion here though, I think you need a good set of vernier calipers & a chronograph or at least access to these before you go much further.
After that neck test & if a smoked dummy round proves that you OAL is okay to work through the magazine without binding yet not overly long to contact the rifling then a chamber cast will definitely be in order!
I'd still watch if the crimp you are applying doesn't 'buckle' the case - it could be a cause as well?
Keep us informed please.