I'd do 1/2-28 without worrying about it. It isn't ideal, but it will work fine. Believe it or not I have seen 1/2 inch threads on sporter weight 300 win mag barrels and the owner reported no problems.
If 1/2-28 isn't to your liking then I would recommend a larger diameter thread and a collar with a larger shoulder as shown above. The face mount on a 5/8-24 thread is also a really good option, but depending on what suppressor you have that might not be an option.