What guns can penetrate what kind of structures?

Solution 1:

The more damage a gun (or class of guns) does, the more likely it is to be able to shoot through objects. That means that LMGs, assault rifles, and sniper rifles are better equipped to shoot through objects than shotguns, SMGs, machine pistols, or handguns. This doesn't apply to launchers, which inflict massive damage but are effectively useless for penetrating objects.

If you want to better shoot through objects, pick a LMG, assault rifle, or sniper rifle and use it a lot in order to increase your weapon proficiency level with that particular weapon. The more you use it, the more proficiency choices you unlock -- including one called Impact, which gives your bullets increased penetration. It's effects are similar to Hardened in Black Ops, Deep Impact in MW, and Full Metal Jacket in MW2.

As for aerial weapons, things that deal bullet damage (the helicopters) are more likely to penetrate objects than the ones that deal explosive damage (a predator missile).

Ultimately, even with with the proper gun and Impact equipped, it is going to take some trial and error to get a feel for when you can shoot through stuff, as some objects are simply easier to penetrate than others, regardless of appearance. One example that springs to mind are the concrete pillars in the center of the map Interchange; they are notoriously easy to shoot through even though they shouldn't be.

Solution 2:

The weapon proficiency 'Impact' increases the bullet penetration of your weapons, just like 'FMJ' from MW2. In general, bullets can only penetrate 'thin' materials (sheet metal, thin walls, fences) but not things like solid walls. Sometimes thin brick walls can be shot through, but there is no hard and fast rule about what can and cannot be penetrated. For those materials that can be penetrated, they cut a certain percentage of damage for all weapons (except for rockets, which have no penetration). However, weapons like sniper rifles will generally penetrate better while weapons like shotguns have terrible penetration. For aerial guns, if you can shoot through a wall with a personal weapon, usually it can be shot through with a aerial weapon. Like portable launchers, aerial missiles have no penetration though sometimes you can kill people through walls with splash damage. Additionally, most guns will break glass allowing you to kill people and most launchers (and the predator) will go through the glass and then blow up, allowing you to kill people on the other side. Sniper rifles are capable of actual penetration kills through glass, since they do not shatter the windows unless it is already damaged.

Solution 3:

Since it hasn't been mentioned already, it is important to look at the wall you want to shoot through. The in-game texture are reasonable facsimiles of the appearance of the real world materials. You wouldn't expect to be able to shoot through stone walls, but soft materials are always worth a try.