Mass Effect

You just have to kill 150 people for the pistol expert achievement. Not actually unlock it in the upgrades.

That's not what he meant. He's saying that he and Garrus were using the rifles, while Kaidan had a pistol. Kaidan fired a shot, killed someone (obviously), and he unlocked the achievement. I'm pretty certain the game also takes into account your squadmate's kills and uses of abilities, but I'm not entirely sure.

Based on my experience, I think our squad members also have the chance to score a hit using the weapons, and the game will record it the way it records my hits.

My Assault Rifle Expert achievement was unlocked after Ashley's hit killed a Geth, my Pistol Expert one was unlocked after Kaidan's hit. I unlocked Shotgun Expert and Sniper Rifle Expert myself with the help of Wrex (for Shotgun Expert, since he has proficiency of that type of weaponry).

My Biotic-related and Engineer-related Expert achievements were unlocked the same way too, thanks to Kaidan's, Tali's and Liara's active role using their own skills (I set the squad member to be actively using their own powers and skills in the game option). I can't confirm this further than I did see the achievement - Throw Mastery - unlocked after Kaidan hit an enemy with Throw. Either the achievements have glitches, or simply our squad members do give us significant (not to mention faster) help to unlock certain Expert/Mastery achievements.

Forgot to explain, Ashley was using Assault Rifle when her hit unlocked Assault Rifle Expert achievement and Kaidan was using pistol when his hit unlocked Pistol Expert one. Wrex was using shotgun, but it was my hit that unlocked the Shotgun Expert achievement. Sniper Rifle Expert achievement was unlocked by myself (since I was the only one in the team who used Sniper Rifle). And when I said hit I mean it kills (only for Expert achievements, since Mastery achievements only require you to use certain skills/powers 75 times, exclude First Aid Specialist, which requires you to use medi-gel 150 times).

I apologize if I made confusion.

the achievments are completely glitched and they accumulate kills and times for biotics/tech oddly. You can use singularity and throw on your mako and still get the acheivements, but not lift and stasis. Some of your party members like Wrex can help you unlock the pistol achievement, but members like Kaiden cannot. Now on BDtS, those patterns are switched to the opposite, its very confusing.

I don't know if this is a glitch, but, kills per weapon/power carry over across game saves.

I started with my first character and used all weapons, and unlocked several achievements. Then I started a second game, and killed about 15 enemies with a specific weapons Achievement Unlocked!

It isnt a glitch your weapon/power count carries over into future games although to get them out of the way i just grinded them out so i dont have to worry about it anymore

This is obviusly a glitch cuz unlocking those achievmentsshepard can only add kills to get them kaiden couldnt help shepard unlock pistol expert unless its a glitch i dont know how it happend but thats a glitch a good glitch.