A weak mounting surface for a vise is trouble. There should be no flex or movement. The correct barrel bushing also helps a lot. I have mine mounted low on my benches 4x4 leg, wrapped and kicked with 2x4’s. The post is not only screwed but through bolted with 1/2” bolts. The low mounting point gives me plenty of leverage on the action wrench and I’m able to give it a good whack if need be. 
Edit: My first Tikka take off I used my brother in law’s hydraulic press with wooden blocks and a barrel bushing. Penetrating oil for days, heat gun on the action, wet frozen towel on the barrel.
Edit: My first Tikka take off I used my brother in law’s hydraulic press with wooden blocks and a barrel bushing. Penetrating oil for days, heat gun on the action, wet frozen towel on the barrel.