It's not that they over-tightened them, it's that they blue them after assembly and bluing salts leak into the threads and form a chemical bond. Kroil or penetrating oil on the threads is your best bet for helping ameliorate that.

I had the same problem awhile back and was dissatisfied with the way the woods blocks worked, so I destructively modified mine to allow the recoil lug and the front action screw to provide additional slippage assiatance. I didn't clean this up as it was just meant for one-time use.....the flanges for the recoil lug to bear against are cut-down 1/8" aluminum angle, screwed in with wood screws...

See below - you probably have stuff in your shop to do this, but if you're going to be switching barrels often, an action wrench is the better solution. But I wanted mine done NOW..

[img width=600 height=450]http://i60.photobucket.com/albums/h28/elkbane/ActionBlocks_1.jpg[/img]

I had to trim the width of the block a little on a table saw to match the distance between the magwell and recoil lug and drill a hole in the bottom for the action screw, then relieve for the recoil lug pin.....But when you put the top block on and mount this in a vise, it's pretty stout - no more slippage.

Elkbane