Shotgun Extended Mags... Bulldog 25 double kills, others only 3?

I'm not sure if anyone noticed this, currently on PC, and unsure if intended. The S12 and the Tac 19 only need 3 double kills for extended mags, however the bull dog needs a whopping 25. I already find the three double kills hard to get considering the duration of time between kills is very short. Along with all the movement it isn't very often I find people close enough together to land a collateral, or let alone kill one and switch targets before they either: shoot back and kill me, or I'm out of ammo.

Any advice however on completing the current challenges (whether this intentionally hard or not) would be appreciated. On PC there is a limited number of games to play... essentially DOM and TDM. Ive only managed to get extended mags for the tac-19 because of HC DOM. The S12 feels like it has to be in melee range to kill someone within 2-3 of the 8 shots, and honestly I've gotten 8 hit markers with it before at a range I surely shouldn't have. The bull dog however seems to be in the middle with damage:fire rate.

I'm also disappointed that ADS doesn't improve the pellet spread (at least on the tac 19). Would make it a bit better and give it a bit of a skill curve.

What do you guys think? A bit excessive? Intended? Advice?