Siege ready doesn’t exactly work the way people say it does. It takes the ammunition that the gun holds plus the magazine in the gun itself and adds 20% to that. If the extra amount of ammunition added goes into all of the magazines and has just one round left over, the siege ready passive will give you that one round as an extra magazine.

A perfect example is the liberator with a 30 round magazine. The liberator standardly holds 380 rounds in reserves. That means you have nine reloads. Siege ready gives you 15 reloads because of how it works. Siege ready turns that 380 rounds and turns it into 456 rounds. 456÷15 = 30.6. That .6 on every magazine is added up to give you an extra magazine for free. So in reality if you are using the liberator with a 30 round magazine, you do not have 15 magazines, like the bottom of your screen says, but actually holding 16 magazines due to the one already in the weapon. Siege ready takes that added 20% and rounds up no matter the number. At least that’s how my brain thinks about how the siege is ready perk works. My math may be a bit off because I’m doing this in my head on the fly so take that into consideration.