Xbox – How to get the ‘Messer Sandman’ and ‘Sweeper’ achievements in Assassin’s Creed 2

I think this may be a bug. I have Veronica and gave her the Q-35. She was doing fine until I saw her shooting her stock 10mm at a giant radscorpion. I look in her inventory, no Q-35. I use a console code to give myself another one, and give it back to her (items are created with full CND). She did not equip nor drop it, I checked her inventory again and... no Q-35.

I loaded from before I gave it back to her, generated another one and put it in her inventory, saw it sitting there before I closed it, transferred it back to me and her a couple times, and now it seems like it's staying there. For now, anyway.

This is definitely sounding like a bug though, unless I'm missing something.

I got both of these during story missions.
The car one I got in the first mission where you have the cars (shrouded bunker), there a part where you enter a porch overlooking a room, with a short spiral staircase on the right, enemies tend to bottleneck just after the stairs, you can hide behind the porch's rail and send cars down the stairs, with some luck you'd get to the enemies before they blow up the cars and blow up 3-5 of them. I managed to do this on Nightmare after a few tries.
I got the arrow one during the prison break mission just after releasing the prisoner, there was a a part when he's busy hacking and you have to fend off enemies, a few guards grouped near the left side of this area and I shot one with an arrow and it got the job done. A better opportunity was in Dead City Reverse, there was a part where you watch a few soldiers fight off mutants, while they were busy with the mutants, I used my arrows and blew them all up.
If you're past these missions, I recommend doing this either on Bash TV, sewer missions (DLC) or later in the game in the distillery missions, there will be parts where you're on a ledge and multiple mutants will climb over, I think this will be a good place to try the trophies although I didn't get them there myself.