Well, I guess I'm a little late on this, but, since I finally joined the forum (after just stalking for a long time) because of this thread, I'm going to post anyway.
I'm far from a pro (gunsmith, but could be applied pretty well to anything!), but I've taken off a few barrels. A recent one was quite stubborn. A good vise is key, as has been discussed, and penetrating oils always help. A sharp impact to break things loose is also important, especially with thread lock. What we stumbled on was to use BOTH action wrench types. Tried the Brownell's wrench first, as it has always worked before. Couldn't break it loose, even with hammer blows. Went over to a neighbor that also smiths a little and tried his that slides into the action, with no luck, and I was getting nervous about messing up the action. Put the wrench on the outside with hard steady torque, and put the other wrench on a battery powered impact (has a 1/2" square for a break over bar). Took about 5 blows from the impact wrench to break it loose! Luckily, not a mark anywhere.
Enjoyed the thread, and thanks for getting me off the fence about joining.