I've had the exact problem with Laser Cast 155 gr bullets. I loaded my first ammo on my new Hornady L&L AP today using these bullets in Win. cases and had the same problem again. As soon as I get my Unique and these 155 gr lead bullets used up, I'm done. I'll go with the West Coast copper clad bullets which have worked very well in the past.
I don't know what is causing the problem. I've measured and measured (OAL 1.12). I've tried different seating depths and different taper crimps. Most loads chamber OK but a few don't seat deep enough. The West Coast are .001 less in dia. I believe. One thing I did find on the lead bullets was that, every once in awhile, a small ridge of lube or a fine hair of lead will show up and this can cause some chambering problems.