Need to put a scope on a M107 CQ. Going to use a Vortex Viper 5-25 PST I got for really cheap. The Barrett zero gap rings seem to be out of stock most places. I was digging around my junk pile and found an American Defense QD 30mm mount.  Will this be adequate?

My experience with locking lever and/or cantilever mounts is
the 50's recoil destroys them.  Larue's triple lock mount appears
to hold up but it is very $$$.

Currently use Barrett Zero Gap rings with no issues.

Probably. If it craps the bed, you can use vortex’s/adm’s warranty.

I personally spring for Spuhr ISMS, but in all reality its likely overkill. Barrett semi-auto recoil is incredibly soft. Its less than most hunting rifles.

I'm in the same boat.  Can't really find the Barrett zero gap rings that I want to use on my new glass.  I'm really leaning towards the Badger Max 50's in Steel.  They are true beasts, heavy and bomb proof.  They run $186.  The only problem of course is they are standard rings and will require leveling during mounting which at least for me anyway is always a PITA.  The Badgers are in stock now which is good and they are probably the strongest rings on the market.  Something to consider.