First, does the sizing die just touch the shell holder? If not, screw it down until it does.
Do the sized cases drop in barrel and go "plunk?" If not, the sizing die is badly adjusted or it has a problem.
Next, take a round that doesn't drop in and chamber and paint the bullet and case black (Magic Marker works well).
With barrel in one hand, drop round in chamber and twist back-and-fourth once or twice. Remove and note where chamber has scratched the coating.
If on bullet, COL is too long (each bullet can require its own COL)
If on case mouth edge, you need a bit more crimp
If just below case mouth, you are crushing the case with too much crimp.
If on case where the base of bullet is located, you are seating the bullet crooked.
If on case just above extractor groove, you have a case bulge not removed during sizing.
Do this and tell us where your problem is.
Don't manuals cover this any more?