1) I use a Dillon seating die with a homemade seating anvil.


Also works on XTP and HAP bullets.
My OAL is all over the place and I would like to get some consistency out of the Dillon 650.
2) Variations in OAL can be the seating anvil, but on a
progressive press these typically involve issues at the Sizing Station which is occurring concurrently. Generally the issue is related to lack of
lubrication. While it is true that with carbide dies you won't
need lubrication, but that doesn't mean that lubrication
won't help eliminate your problem.
What I do is knock all the cases (100 to 500) to be loaded over onto their side on a towel used only for spray lube. Then I give the group 2 shots of
Dillon Case Lube from 3 feet away, and roll them up in the towel and use the towel to jostle them around. Then I immediately pour the contents of the towel into the case feeder. This adds a whopping 1 minute onto my loading time. Been doing it this way for about 5 years and I've used up a 1/4 of a bottle. [
Hornady One Shot will do the same thing, but you'll need to pour the brass into a zip lock bag and wait 24 hours.]
It's quick, it's easy, it's inexpensive, and it makes all the difference in the world.
Hope this helps