As a player, I use Chummer for character creation, so when I've gotten the character approved by the GM I'll move him to career mode. Then I go to the weapons tab, where Chummer allows you to "Load" the weapon with ammo. Then in-game, I just click the "Fire" button in Chummer, and it subtracts the round(s) fired automatically. When it hits zero in the current clip, I have to click "Reload", assuming I have enough ammo left.
Also leads to the occasional piece of hilarious awesomeness:
We were in a minor fire-fight because a new guy in the group, who was new and still thinking like D&D (aka "bust in and kill everything"), decided to kick down the door and start shooting when we were just supposed to go talk to some low-life thugs.
Bullets were flying, but we needed to keep someone alive for questioning, so another player (a sniper/infiltrator using a Barrett with a dual-mag modification) decided to peg one of the guys with a stick'n'shock. He was using Chummer, and had the wrong magazine selected when he his "Fire!"
The other magazine was loaded with APDS.
Instead of being all "Oops, lemme fix this," he rolled with it and decided that
his character had derped up and had the wrong magazine selected. Thus resulting resulting in the exchange of:
"Oops..."
"Whadda ya mean 'Oops'. You blew the guy's fraggin' head apart in one shot!"
"Yeah, but I meant to use Stick'n'Shock."
"Oh. Well, not like he's the last one left, right?"