Re: How to remove a factory base from a Sako TRG??
The powder was the Loctite after heat broke it down and the threads "ground" it on the way out. It would likely be white, but you may see traces of blue or red (or another color as there are tons of thread lockers, not all by Loctite.
As Ramius pointed out, there is also a bedding compound between the surfaces both to lock the two together and to prevent water ingress which can cause rust. Amusing factoid... rust is c. 9x thicker than the metal it replaces. So if rust eats .001" into metal, the rust/oxide protrudes .009" above the metal. This is why rusted bolts are so hard to remove and rusty metal appears to grow and extrude (look at really old rusty car springs.) Technical term is rust smacking. Because of this, rust under scope mount = changed zero.
Good work getting them off! You can reinstall w. blue loctite or similar. That will work as bedding compound, too, just use thin layer. cheers, sirhr.