I Like to think I'm pretty good at bo2 and have about 200 15 gun streak medals can't get a gun streak over 15 in mw3???
MW3 doesn't have as many head glitch locations as BO2 does which does play a part in the difference. However, the biggest difference and likely your issue is gun kick/flinch. In MW3 the guns don't always kick straight up and the gun flinch is basically the same as BO2 without toughness. You can reduce the gun flinch by using the focus proficiency. That will help you make the guns feel more like BO2 guns. Or you have to adjust your aim lower to compensate for the kick mechanics. If I remember correctly upper abs is what you want to aim for.
Edit: I actually played MW3 last night for the first time in many months and I don't know if it was lag (I don't think that it was) but I got killed a number of times by guys that hadn't even turned the corner yet on my screen. I suspect though that it wasn't lag so much but rather bad camera angles that made my routes poor. I'm sure that when I used to play MW3 regularly I instinctively hugged the right corners and avoided these issues but being a noob again I basically made my enemies job a lot easier by giving them a full view shot on me while my view of them was completely obstructed. Granted there may have been some lag involved that contributed to this problem as well but generally speaking when I engaged them in the open I didn't have much trouble killing them. So the lag couldn't have been too bad even though I had zero chance of winning.
Edit: I actually played MW3 last night for the first time in many months and I don't know if it was lag (I don't think that it was) but I got killed a number of times by guys that hadn't even turned the corner yet on my screen.
And this, is why I sold the game
Basically, MW3 requires more skill, BO2 the skill gap is reduced. So that would be why.
MW3 doesn't have the option for target assist for multiplayer also like BO2 does.........Like the other guy said focus proficiency will help.........
MW2 and MW3 multiplayer doesnt have the aim assist option;nevertheless, both the campaigns have the aim assist option though......... I just got done playing both MW2 and MW3 and I didnt see any option for aim assist on the multiplayer side
You don't have the option to turn Aim Assist off in MW3. It's on all the time. If you'd like to test it, just go into any match and ADS without firing while an enemy walks by. Technically firing has nothing to do with the Aim Assist but not having the muzzle flash makes it easier to notice how you will get pulled towards your target.