Does expertise add damage per pellet or to the base damage of shotgun attacks?

[ringring]

Even with barrel stare and sixth shell with full specialization and full auto, I feel like my 8.6 steel cat does more damage, since with rapid reloader and spec ops, it can burst twice, fires 9 rounds per burst with a muzzle break, can use inferno and W2C rounds, and adds the expertise damage bonus to each shot.

[ringring]

speaking of which, is there any reason not to use 12p or 6p on invictus, since he has no armor?

Lol, just read the wiki, i guess expertise doesn't work with shotguns at all.

[cypherusuh]

speaking of which, is there any reason not to use 12p or 6p on invictus, since he has no armor?

I assumed that you means the last guy on Arena

if so, he has pretty good mechanical DR from Conditioning perk + 16 CON
in my experience playing shotty 2 years ago, I feel like you should go on either 20p or 3p tungsten most of the time.
it also depends on difficulty. hard and above, you still able to use 6p most of the time, but at certain point, 3p would be much better option.

or, you could just save the game BEFORE entering the arena and see the damage for yourself