My first thought; Is this a once fired AA hull you're using? If that's the case it may be fire-formed to the chambers & rims of the gun the hull was fired from.

I have a model-21 Winchester that I had a similar problem with. The once-fired AA hull was tight in the chamber & it wouldn't let the gun close. I then tried a new AA shell and it dropped right in & the gun closed without an issue. My conclusion was the once fired hull had expanded to the chambers of the gun it had been fired in previously.

Just a thought.