I've got 2000 kills with the Executioner, most of them Dual Wield. With the Shield setup I suggested, all maps are your friend. You'd be surprised at how good it is on the bigger maps. Since you'll run into a lot more people ADS'ing their line of sight or trying to snipe.
I recently golded the executioner last weekend and here are a few of my pointers if interested.
I mainly play HC but I found that its easier to get the challenges and headshots in core.
My setup was dualwield for attachments, which also acts as fast mags.
perks were ghost, scavenger, toughness, and dex.
Corner camp often, always try to throw concussions at enemies, and try to ambush rooms that are known sniper locations for the easy headshots.
dual wield and try to aim up as you shoot, you will love it in core for the improved health that you have.
But overall, it is a long road and it sucks and it will get you pissed off but eventually it will be done if you camp and camp alot.
When you go for bloodthristies and double kills, it will suck even more.
It is the only gun that I was not comfortable doing both the no perks and no attachments together. I did them seperately and dropped dual wield and used suppressor and fast mags. double kills are easier to obtain if you can limit the first target to one or two bullets which is not hard to do once you get used to the gun. Bloodthirsties requires you to camp ALOT. Just camp and good luck.
Play how I did in those 2 videos. Use the class I suggested but instead of the Concussion Grenade, use a Tactical Insertion. The Executioner honestly was the easiest gun I got gold and the most fun I had. I did the no perks/attachments together. Ended up getting all the bloodthirsties, doubles, and revenges as I did the 150 no perk/attachment challenges.
Oh I finished with the executioner already. I had a much more harder time with it than you must have had. I agree with you though it actually a fun gun to use trying to get the double kills challenge once I knew how to conserve the bullets.
Play FFA, spam concussions when you get a hit sprint over to the guy and you will have plenty of time to line up an easy headshot, resupply of the corpse and repeat. Once you learn the FFA spawns this technique is really effective so long as people don't wise up and put Tac. Mask on which hardly ever happens, if they do just find a new lobby. Can get between 10-20 headshots per game doing this with any weapon.