So what are you saying is that the adult xenos can be killed only by assault rifle, shotgun, etc.? No way. Its not possible. Its a tissue after all, its not metal.
Btw the revolver in the game seems way more powerful than the pistols used in A:R and in the movie one bullet to the head killed an adult xeno. The revolver in the game should be able to kill the xeno. It looks like its bigger caliber judging by its barrel and punch. (as someone already mentioned)
Thats bullshit man. You can kill a xeno even with melee weapon. Why the predator is hunting xenos with spear and wrist blade if the xenos were UNKILLABLE like some people think? You are not limited to firearms only. Its funny to think you are.
Can you show me a screen where I can see the mechanical part of a xeno?
I think you are making several wrong assumptions here.
Firstly, tissue. It's Alien tissue, which has been described as needing a laser scalper to cut, and that's just the face hugger stage. Also, it has claws that can rend through steel. It's makeup has been described by the creators as a bio-mechanical silicon based life form, with an external exoskeleton carapace that is like armor.
Secondly, when you talk about firearms and bullets, you need to understand that it's not the gun that damages, its the bullet. There are many types of bullets, ranging from solid lead rounds to armor piercing high explosive. You can have the biggest gun in town with the largest caliber, but if your bullet is a soft lead round which flattens on impact, it's not going to be able to penetrate armor. This is why a small handgun with APHE bullets can be said to be more effective than a rifle shooting lead. FYI, the pulse rifle uses HVAPHE rounds, which can cut through an alien. However, I find it ridiculous that people think a shotgun firing ball bearings can even hurt an alien, like the games assume. The only time it ever got a kill was at point blank range in the mouth, or using high-tech plotbunium ammo. Speaking of which, all the A:R weapons that the team brought in are stated to be souped up beyond what is legal, thus their welcome.
Third, are you trying to compare what a superhuman alien species that can jump 5 meters into the air, and has metal that is made to combat the aliens acid blood, can do to an alien, to what a colonial marine with a USCM K-Bar can do? Or in this case, what one fit female civilian with a wrench can do?