I think that with the fact that you are shooting factory new and getting stuck that full lenght sizeing is not comming into play here...I would pull a couple bullets of each brand and check the size of the cases from the factory before shooting them...and check a couple you already shot and see what the difference is....
Also with the Horandy is that the "top of the line" horandy.. If so manybe it is to much for your gun.
Also is this a new gun or a new gun to you?..maybe something might just be wore out enough that with the higher quality ammo it is a little much for it.
A couple pics of the fired brass might let someone on here see something that you are not...more eyes the better.