Does anyone know of a mag extension that will fit a Weatherby SA 459, or a EAA 612 tac?
Thanks!

Yes, just put an extension on my SA-459 that I bought in Dec 2020. All Nordic Components stuff. I got the nut for the Benelli Nova/ Supernova, the +3 extension kit, and the clamp for the heavy Mossberg. I cut the spring so 20” is sticking out of mag tube and it works great.
My SA-459 is black with the 22” barrel. With the +3 extension, the mag tube is about a half an inch shorter than the barrel.
With the clamp I also ordered the pic rail and quick disc mount (for a later sling).
Nut- Nut-BR-12-00, clamp with pic rail- BCT-12-MB, tube +3 MXT-TBS-12-3K, quick disc mount-QDA-BCL-ASM.
I only had to grind and sand down a small lip on the end of the factory mag tube.