Shi - You are paying a lot for that upper, but it will definitely handle the pressure of the .50 Beowulf in the chamber.
I do not believe that you NEED to go to this extreme, but this upper is what I would classify as "Fire and Forget". You buy it once, you don't need to worry about it. If I was inclined to build a weapon of this magnitude, and I was willing to PAY for a custom barrel with a custom chamber, I would be looking for "Fire and Forget" parts. Take that for what you will.
Now, the downside. You are providing a solution that there isn't a problem. You don't NEED a specialized upper when the people that pioneered the round, put out their own upper in the first place.
Might I suggest this prebuilt and tested upper??
The barrel is NOT a good choice, in my opinion, if you are building a PIG gun. One that you are looking at really delivering the goods to a hostile animal.
Please notice this caveat:
Enlargment of the feedramps and ejection port to 0.637" will be required for proper function
You are not buying a "ready to go the field" barrel my friend. You are buying a "roughed in barrel" that will require specialized parts that, IMHO, will end up costing you MORE
than if you just went to the Alexander Arms folks in the first place.
Shi, when you are looking at building a wildcat platform, you need to decide if you are going 100% custom ( because the ammo is custom ) or if you are going to go piece meal and build what is available on the market.
If you are looking at a cost effective build, I would look a complete and tested upper, with a custom lower that you build yourself. Or I would look at having a custom gunsmith build you a complete gun and going that route.
"In between" is not going to give you what you are looking for in this build.