Best rifle caliber

[BlindSpot]

I don't hate the 5.56, but I don't love it either. At best I'll say it's an adequate round for its intended purpose when fired from the longer barreled M16. It's been problematic in the M4 though. I don't know that I would want something as heavy as the 7.62. That's made more for a full sized battle rifle than an assault rifle. I'd love to see the military seriously consider the 6.5grendel or 6.8spc.

[OVERKILL]

I'd love to see the military seriously consider the 6.5grendel or 6.8spc.

 So would I. Only a slight weight increase and couple less rounds in the same size mags or slightly longer rounds for the same capacity, but the effectiveness is greatly increased. I don't own a 6.5 Grendel yet, but I am doing my research and intend to start seriously looking for one after the first of the year and finances straighten out.

[Labdwakin]

.223- availability, penetration of the cranial cavity, typically semi-auto
9mm- availability, cranial penetration, same ammo for carbine and pistol
45 acp- same reasons as 9mm

Let's face it, the simpler you make your life in the aftermath, the better.  Worrying about engaging something that can't move as fast as  you can at anything over 150 yards is impractical at best.  You really don't need more than 150 yards of MOA accuracy for a Z weapon.  My overall fave is the 45 ACP carbine for this task because most of them have a pistol counterpart that accepts the same magazines.  STANDARDIZATION, STANDARDIZATION, STANDARDIZATION.  Don't put yourself in a position where you could lose a gun but have ammo you can't use anymore.

[OVERKILL]

 Having a carbine and a pistol chambered for the same cartridge kinda follows the "2 is 1, 1 is none" theory, if one messes up you have a backup.

 Labdwakin, If you had to choose between carrying a 9mm pistol and carbine or the 45 pistol/carbine combo, which would you choose?

[Labdwakin]

I would most likely go with a Glock 21 45 ACP... you can get hi-cap mags that hold 27 rounds.  9mm might be more available as ammo, but you'll eventually be to the point that you're disassembling any ammo you find for components to load whatever you have.  45 acp is more forgiving with cast lead projectiles than the 9mm and doesn't require as much precision in the shooting. Let's face it, when you're running/fighting for your life, you're not going to be shooting with benchrest accuracy.  You would have to expend over half a million rounds to achieve the proficiency needed to be as deadly with a 9mm as you can be if you're just competent with a 45.