I tried to load up some Lott rounds last night, but to no avail. It appears as if the brass has been resized to a smaller diameter than needed by the Hornady dies I have.

Also, when I tried to seat a 350gr Speer, the bullet kept getting grabbed by the seater plug and then pulled from the case. I flared the case mouth with the die provided in the Hornady set just like I would with my other straight walled cartridges. Has anyone else experienced similar happenings?

Yes. I bought a set of Hornady dies in .450 x 3 1/4" Nitro Express and found them worthless. The size die would not size Hornady case mouths enough to hold any .458" jacketed bullet and there were problems with the seater die, too. Bought an RCBS size die and a Meacham seater die and both worked perfectly. I have about 100 die sets from all makers, and Hornady is my least favorite by far.

Hornady Lott dies create a ghost shoulder when resizing(makes the case look wasp waisted) nothing u can do for that Hornady makes it that way on purpose I have no idea why. I sent mine back once. They returned it saying it was fine. I found if you resize with a 458 win die u will not get the ghost shoulder

I also had an issue with their seating die and found it had the wrong seating stem installed( mine was a 22 cal stem)

I contacted Hornady and they are sending me a new die body...hopefully it will help.

I had a couple of sets, sold both, do not like the system. I;ll stick with RCBS and REdding..

I was able to get some bullets seated after opening the case mouth a touch more and then I chucked up a bullet into a drill and polished the seater plug with some lapping compound.

After loading, there is a noticeable hourglass shape below the base of the bullets. They camber fine, but it looks rather odd.

Also all of the bulges in the case, made at the base of the bullet, are not concentric with the case...not sure of a solution to that one.

I ran into the same girdle shaped waist under the seated bullet using RCBS dies right off the bat over 25 years ago. To correct this I made up an expander mandrel to slide into the new case that expanded the body and eliminated the waist effect below the bullet position then got a Neil Jones Neck Bushing die size to neck size the 1st .500 of the case ID to .452. By doing so you made a false shoulder under the base of the bullet. I have basically 4 dies I use to size Lott brass and a 5th for special applications. I have loaded many thousands of Lott rounds.

When done to once or twice fired brass the neck sized round was in much better alignment with the throat and lead, I have never had a Lott that wouldn't shoot very well if you could sit behind it.

I have those dies and my Lott reamers for sale if someone is interested.