D.A. fan is back for an ME1 Text Only 'Let's Play' (page 51)

You can purchase an "Offhand Ammo Pack" from one of the shops on the Citadel (the one on the uppermost level).  It increases the ammo capacity of all weapons by 10%.  It is an armor piece (actually a gauntlet), so you'll have to equip it at your armor terminal before you can use it.  The trade off is that you'll lose whatever "boost" your current gauntlets are giving you.  It can also be a little finicky... i.e. sometimes doesn't take effect right at the start of some missions.  It should take effect though after you top up with ammo the first time while on the mission.  You will be acquiring a SR with a larger magazine (48 rounds in 12-round clips) on Thane's recruitment mission (the Viper).  It's not as powerful as the Mantis (which is the SR you were given at the start) but it will fire rounds much more quickly than the Mantis.  You might also have access to the Incisor (which has a 30-shot mag).  However, if fires 3 shots basically at once, so most people can only really get 10 effective shots with it) and, of course, each individual shot is not as powerful as one shot from the Mantis... so some people actually lose out on kills they could have made with the Mantis because the victim starts to ragdoll with the first shot from the Incisor and drops out of the headshot just before the second and third shots hit.

There are a few other ways you can extend your ammo... 1) Be sure to reload before picking up ammo.  That will ensure that you will get full benefit.  If the clip in the weapon is not full, the ammo you pick up will not fill that clip if you're otherwise full.  2) Enemies do seem to drop more ammo if killed quickly.  3) You can save and then reload just after a battle.  Certain "placed" thermal clips will respawn with the reload.  That will enable you to at least go into the next battle with a full load.

One of the challenges I like most about ME2 though is that it does force an infiltrator to be very conserving about their SR ammo and to become adept at switching battlefield tactics to suit the SMG and powers when ammo for the SR runs out.  If you are playing as an infiltrator... you will be given an option (during an upcoming mission) to select a very, very powerful SR, the M-98 Widow (with a 13-shot mag) or acquiring training in an assault rifle or shotgun (giving you another alternative weapon).

I also play Borderlands... great game.  However, I do feel that, for the most part, it can easily get too generous with the ammo between SDUs, mods that can regen, and legendary wepaons that can also regen.  I'm currently in the middle of a Playthrough 2 of the first game... and between my Guardian AR and my Sniper mod, I'm not even looking in any of the ammo crates right now.