If your playing core, never use an SMG, if you want something small run a Kap 4 class. SMG are just to weak, and do not have enough range to be effecient in Core. In Hardcore you will find SMG to be king!
Actually I have been mostly playing HC KC or HC Dom. I think the easy bullet damage has made me complacent when it comes to aiming properly. Maybe a change back to core is needed.
I can't even handle anything core anymore unless im using the remmington Hardcore has me too spoiled. not to mention every 5 steps you have a big icon covering your sight dot telling you, that you can pick up someones else cruddy weapon. It would be nice to play HC FFA though.
If you stay in HC the SCAR or AN are both good choices (I also like the SWAT for HC). They both are also good in Core but for an SMG guy I would recommend the AN over the SCAR. The SCAR feels slightly better to me for mid to long range but the AN is better on short range because those first two bullets come out so quickly.
There have already been some great suggestions that will slow you down. Weapon changes and game mode changes should help. When it comes to games modes, I'd suggest playing hard core.
For me though it took changing my weapon, game mode, and play style. I was an SMG, LW, EC, tag whoring rusher until I hit PM. Learning to quickscope is what helped me the most when it came time to slow things down. It took me a lot time to learn the skill. Not only did slow me down, it improved so many other areas of my game. You'll improve your accuracy will all weapon types. Quickscoping hardwires a good habit of keeping your cross hairs right where they should be. It will help lead to a game play style that is based on anticaption first and reaction second.
I have always sought out the enemy rather than be a player that waits for them to come to me, It will be hard trying to change that mindset.
I have tried to learn to QS a few times but I just can't seem to get it down. I just can't seem to get the kills before they kill me. Most of the time I miss wildly.
There are so many tutorial vids on youtube but a lot are contradictory to each other. I would really like to get better at it as I liked to snipe in MW3.
Dedicating myself to getting diamond ARs is what has slowed me down. Now don't get me wrong, I do go back to my roots on maps like Nuketown and Hijacked by running a shotty or a SMG. Play with a gun like the SMR or FAL (in HC, most of the time they are 1 shot kills), being single shot they will slow you down because you'll have to think more. Also what everyone else has said about HC, learn to love it
Thanks, I do like the FAL, I have it at prestige 1. I must admit to never having played with it in HC. It could be another way to get me thinking again.