I removed the first 788 barrel i've ever done today. Actually, been working on it intermittently for a couple of weeks.

It is the hardest factory barrel I believe I have ever removed. It wouldn't hold in my old two bolt barrel vise with lead blocks. I heated it. I oiled and let set. I smoked the oil off and added more oil while hot. Added some though the action screw and scope mount holes. Heated more.
Let it set and tried every few days. It wouldn't give up. I've removed hundreds of barrels that way.

I made a new barrel vise with 4 -3/4" x8 bolts. Wouldn't hold with lead blocks and powdered sugar. Made a set of blocks out of a 4x4 and they wouldn't hold. Made a set out of dense walnut, and with powder sugar, they finally held. The wrench had to be put on unusually tight, because it would slip, with the usual sugar and drywall paper tape. With a 6 foot cheater on it, the barrel grudgingly gave way, and then I had to loosen the action wrench because it had to be tight enough to pinch the action tight. It still took the wrench to turn it maybe 4 turns before it got loose enough to come off by hand. The threads were more or less clean, not rusted, but filled with black crud from heating and oiling. Really was just a lot of torque, plus tight fitting threads.

Is this usual for 788's? I've never had a 700 take this much effort.

Is it possible you have a little "give" in the vise? It has to be rock solid. Kinda like when you are removing a tight pin. Must back it with an immovable object. You also might try striking the wrench handle with a 5lb dead blow hammer to impact it loose.

I use hard maple blocks and rosin; in a 20 ton hydraulic press. Nothing can get past that. I threw my bolted barrel vise away decades ago.
Heatng and oil never works because it ain't the threads that are tight; it is the galling of the shoulder. Unless they are glued in and even unheated epoxy will give. You know that.

Over the years, I have made fitted blocks out of aluminum...Never found a barrel that I couldn t take off...and never a scratch...on barrels I really want to protect, I find a layer of adding machine tape works 100%

I need to make up a new set of aluminum blocks. I know I have some I made up to fit standard 700 contours a few years back, but couldn't find them. I really have done almost no work for 6 years, and for the 8 prior to that I had access to a friends shop with a hydraulic press and all the blocks for tough barrels. My own stuff was adequate for the single shots I usually work on, and for the occasional Mauser or Remington 700. Most everything I do is octagon barrel, so except for getting the old barrel off, it's pretty easy.

My new vise is stout enough, and I have a real good Remington wrench. My old 2 bolt vise was about like Woodhunters, the new one is overkill. This barrel was not the usual high torque, release with a snap that I expect. It was gummy and hard to move for about 4 turns after it broke loose. Hitting the wrench with a hammer did nothing for it, it took hard pulling on a long pipe extension to make it move.

An hour in the ultrasonic and some solvent brushing for the action, and wire brushing the goo out of the barrel threads and it will hand spin on just like you would expect. I think it was thread locked. The goo on the barrel threads was persistent, hard to get off with a wire brush.

I have taken a lot of 788 barrels off over the years, and never had one that bad.

However in the 1980's Remington had a issue with bluing salts staying in the threads of M700's and then the salts creeping out months after the rifle was shipped to the retail store. They did a change in the bluing process and got rid of that issue.

With the 788 there is a reduced section in the factory barrel shank so the front guard screw would not bugger up the barrel threads. But by doing that it opened up a very nice recess for the bluing salts to go into and stay. This might be what you encountered, simply some old salts.

FYI, in 1980 we thru away all the powdered sugar and rosin for use on the barrel blocks if you did not want to re-use the barrel. We swept up gallons of Mt St Helens ash. I am down now to about 1 gallon if it left but a little dab or two of the ash on the blocks goes a long way.

J Wisner