Since the game is horrible and don't provide any numbers, I did some observations in the testing grounds. Note that the damage numbers are based on best guesses due to the ridiculous amount of RNG and damage bonus against "thin" armor (whatever that means).
All ranges listed are only view ranges.
*Tier* Sniper Mortar AT
10 500m 225m 275m, 250dmg, +35% (HEAT-MP)
9 500m 225m 275m, 250dmg, +35% (HEAT-MP)
8 450m 200m 260m, 200dmg, +35%
7 450m 200m 260m, 230dmg, +25%
6 450m 200m 260m, 225dmg, +25%
5 400m 200m 260m, 200dmg, +25%
4 400m 200m 260m, 185dmg, +25%
3 400m 200m 250m, 180dmg, +25%
The reload times of AT infantry and mortar are 4s, this is consistent across all tiers.
AT infantry will only fire at targets within their view range. Mortars have ranges of approximately 250-300 350m, this might be influenced by tier but I haven't been able to reliably test it yet.