Ok I went in to take a look at the game to try and see what is going on.
The first test I did was to create a Bronze game and I took the Talon and Crusader and Cryo II Ammo (should be 1.4 rating). Was running my GTS.
Basically the idea was that the Talon if it uses the standard formula would have a "chance" of 1.12 that way, meaning it is always greater than the FRand() output (between 0 and 1) and so should always freeze if it hits a pellet on health. If it was using a modified rate of fire, it would be only be 0.14 per pellet.
The short answer is it seemed I could freeze them with a single shot, the only exception being kill shots.
Crusader testing was problematic with this setup because it had extended barrel and would one-shot CATs on that difficulty. More on this weapon later.
So I went to SP and loaded up an Soldier game and respec'd to give myself Level 3 Cryo Ammo (should be 1.3 rating). Went to Armax, set match to Cerberus footsoldiers, and took Talon w/ ext mag and Cranial Trauma. Same thing, I had no issue freezing CATs in a single shot, provided it wasn't the shot that killed them.
After failing a test for the Crusader at Armax (I had too much weapon damage from passive I guess), I went back to MP and tried out a Silver game with Battlemaster and the Crusader with no damage barrels. Took Cryo I ammo (rating 1.0). Using the standard formula it should have a 0.75 freeze chance, and with the shotgun formula it would be only be 0.09. It usually froze the CAT's when I shot it, so it was almost certainly closer to 0.75 than 0.09 unless I was getting extremely lucky with the FRand() function.
If you were having issue with the Talon, I am not sure what the problem was. What enemies were you trying to hit? If it was Cannibals or Husks, I don't think pellets that hit armor can proc. Also, the pellet has to hit health, not shields or barrier to freeze.
I might take a look in the script viewer again to see if I can figure out if it is defining shotguns differently than I thought. I could have tried testing a low damage, inaccurate shotgun, maybe tomorrow. Might PM someone and ask if they know about what it is doing.