OMG! Why did it take me so long to start using the SMR in Hardcore game modes? This gun is an absolute beast like no other! Forget OHK sniper rifles/shotguns in HC mode, if you want a versatile OHK weapon, this is the gun to use.
Now, I'm sure a lot of you already know about how beastly this weapon is in HC mode, but for those who don't know about it, I suggest you give it a try. It's not a weapon you want to be rushing around with since you'll want to ADS to get accurate shots. Yes, you can hip fire it, but unless you barrel-stuff the enemy, it might not work in your favor to well. Instead, I find it best to take advantage of it's long range OHK capabilities and I use it to flank the enemies while being able to pick them off from long ranges. In games like Domination, you can flank to a spot, take cover, and pick them off in/near their spawn as your teammates get the B flag. If you can get yourself in a nice spot, it could be very hard for the enemy to get you out of there. Yes, you could call it camping, but I think of it as playing defensively...
Similar can be done with a sniper rifle, but what I like most about the SMR is the quick follow up shots you have as well as a clearer view of the enemies. If you miss a shot, you can follow up with many more. Or if there's more than one enemy, you can fire in quick succession. Also, the weapon does have great collateral capabilities, so sometimes, you'll just need one shot to take out 2-3 enemies if they line up nicely.
My class recommendation that I use for this weapon is:
SMR w/ Quickdraw + Stock
Dexterity + Extreme Conditioning
Trophy System x 2
Perk 3 Greed
Here, you are about to get to your position quickly and can start taking out of your enemies. You'll want to find spots that provide you a lot of cover as well force you enemy into the open to try and take you out. Or you force them to go other routes that are covered by your teammates. The Trophy systems are use because they'll try to grenade you or flash/concuss you out of your spot. And the best thing to do to stay alive is to use good judgement. If you think they're not going to challenge you anymore, move up to a new position and take them out. Or if it's getting to be too much to handle, back off a bit to where you you're near your teammates so you have more cover.
Anyway, this is my class set-up for this weapon in HC mode.