Three challenges in particular were ultimate endurance tests for me on account of the map design and stat tracking. Longshots, penetration kills and X kills affected by tactical equipment.
Shipment 24/7 does have the opportunity for longshots, but it's inconsistent since Shipment IS a small map. Through experience, I learned that a
"longshot" kill can vary between weapon classes. The average range is 38 meters, but pistols, SMGs, shotguns have a shorter criteria. I generally play with assualt rifles, so I would have to go to War, OG Moshpit or Hardcore for those challenges. MWIII does not always have great sight lines with its base maps. Back up as far as you can and use single shot/semi auto for maximum accuracy.
Penetration kills were the worst. Again, MWIII's base maps are inconsistent with having shootable terrain. Penetration kills count when your UI marker would say "Wall Bang." You could shoot through doors, sheet metal, wire fences, and some props. Sometimes, a prop would be vulnerable to gunfire if you could catch an enemy behind cover. I think there's a drop off with damage through penetration with some guns.
I found that the OG Moshpit (MW2 maps remade for MWII/MWIII) have ample opportunity for penetration kills. Scrapyard, in particular, has the perfect layout for penetration kills. One of the warehouses on either side of the map has a chain link fence that you could shoot from with a great sight line through either entrance. But, you'd have to have a bit of distance between the fence for it to count. If you're up close to the fence, it won't count. If it's an objective mode like Hardpoint or Domination on Scrapyard, you could farm wall bang kills since they'll be concentrated in one area.
Now, we have X kills affected by tactical equipment. SMGs love this challenge. Flash and stun grenades count, not decoys, tear gas or smoke from my experience. The middle choke point in Shipment helped tremendously, espeically for Domination and Hardpoint. However, you'd have to obtain the kill as soon as they're stunned/flashed. That's about a 1-2 second window if the hitmarker confirmed a hit. The blessing and curse with Shipment is that it's too small. I cannot count the amount of times I missed the window, get killed from all angles, or be one bullet shy of a kill.
. Even the biggest fans are griefing the franchise and only open shills or biggest cocksuckers are left. Remember the good times, if you want you can try to play the older titles using third party clients on PC. Playerbase is still active, even in games like COD 1 and COD 2. Just remember that playing without third party software is a bad idea, your computer or steam account could get compromised and god knows how console servers look like by this point. Last I played BO2 on my Xbox the game was hacked so that the game turned into some Fortnite hybrid where hackers were building "bridges" out of Care Package crates in the mid-air, I left and didn't look back so that my double-master prestige bandaid account wouldn't get de-leveled.
