Okay...
On the actions... there are a few. You have the "shell holder" style single shots, the classic bolt action, recoil operated semi-auto's and gas operated semi-auto's.
The semi-automatics do mitigate recoil somewhat and guns like the Barrett which operate from a short recoil lock-up principle can see reliability issues with some suppressors due to the added weight and counter-recoil tendecies of the suppressor. However, the recoil reduction of a semi-auto is very limited due to the cartridge we are discussing. It's still gonna let you know it's there.
On the example you give, the M82, if I remember the numbers correctly, the AWC Turbodyne decreases the felt recoil by 50-60% when the suppressor is tuned to the gun. When it isn't, the recoil reduction is 30-40% give or take a few percent.
In all honesty, the bolt actions and single shots are the best choices for suppressing. They benefit the most from the other advantages offered by suppression. The most critical aspect is accuracy... especially over long ranges.
Make sure that if you do look into getting a .50 BMG, never, ever shoot it without the muzzle brake or a suppressor. You can be seriously injured if you fuck up your hold or are inexperienced with this round.
Hope this helps!
Mike