Sorry for being a bit late.dtma42
How does the 420 feel on your AR10?
I am considering the same scope, but was concerned it might feel too chunky/top-heavy -- I have a Seekins SP10.
Also, what mount are you using for it?
If not too much trouble, could you post a photo of it from the side?
The chunky/top-heavy thing is honestly really dependent on what you're used to. If you're used to using something lightweight like a Leupold Mark 4 10x with ultralight rings, yeah I can see feeling a difference here. I'm coming from running this with an S&B PMII 5-25x, so it's lighter and quite a bit shorter. With that said, this setup isn't awkward to move around in, doesn't feel like it wants to topple over on me or anything. Hope that answers your question.
The mount here is a Spuhr 6602. 20moa, 1.5" height.
And the pic from the side that you asked for: