Quoted: Due to current envents in my life I am getting ride of a few hobbies ($) and my firearms hobby is going to take a big hit here. I am thining down to two weapons, a pistol for carry and a SHTF rifle. Sad, yes but I dont want to get into that... anyway, here is the scenario: If a man could have only one rifle and that rifles primary duty would be as a SHTF rifle, able to kill large animals for food and used in defence of family and home, rifle would need to be good in a brushy enviroment as well as the open flat ground out to say 400-500 yards. What rifle and caliber of the following would you pick and why? AR-15, 5.56mm standard 20" A2 AK-47, 7.62x39mm AK-74, 5.45x39mm PTR91, 7.62x51 M1A, 7.62x51

From your list I'd advise 2.

AR-15, 5.56mm standard 20" A2

AK-74, 5.45x39mm

out of that bunch-m1a, personally I'd rather have the AR, but you said hunting large animals

Quoted: Due to current events in my life I am getting ride of a few hobbies ($) and my firearms hobby is going to take a big hit here. I am thining down to two weapons, a pistol for carry and a SHTF rifle. Sad, yes but I dont want to get into that... anyway, here is the scenario: If a man could have only one rifle and that rifles primary duty would be as a SHTF rifle, able to kill large animals for food and used in defence of family and home, rifle would need to be good in a brushy enviroment as well as the open flat ground out to say 400-500 yards. What rifle and caliber of the following would you pick and why? AR-15, 5.56mm standard 20" A2 AK-47, 7.62x39mm AK-74, 5.45x39mm PTR91, 7.62x51 M1A, 7.62x51

I applaud you.  We get this question semi-monthly.  Most people don't bother to define the mission and then select a rifle to meet the mission.  You are in the 95th percentile on that procedure.  I want to check some of your assumptions though.

400-500 yards engagement range.  Why?

In a SHTF you are a lone actor/microunit entity.  I say "Microunit" because you aren't even five members strong.  You don't have the ability to fix enemy with covering fire and maneuver to kill it because you don't have command and control of even small unit mobile forces.  Therefore you sort of have two options:

1.  Fixed Point Defense. (House, home, property) with the hope that you won't be flanked by a sophisticated small unit tactics enemy.  Not a particularly good hope to be making in SHTF since natural selection would hint that your enemy, if still alive, is somewhat sophisticated and motivated.
2.  Low Intensity Defense.  (Your distinct advantages are high mobility for a ground force (no logistics challenges, no communication issues between units) and familiarity with the local area.  You also have preparation time.  It is a meeting engagement for the enemy, but not for you if you prepare properly.

Fix point defense in a lone actor situation is a bad idea since it is quite easy to figure that in a SHTF situation you are outnumbered 3:1 or potentially FAR higher.  My doctrine in SHTF environment with lone actor/microunit forces is escape and evade down to inside 50-75 yards (where you can actually see and reliably engage all the targets you may have to deal with) and engage from field expedient, prepared positions.  Given that you have no idea what reserves or backup or communication hostiles may be possessed of, anything with any level of enemy force is an E&E problem for a lone actor.  Dispatching anyone, even trespassers, is a last resort.  Even MORE so with SHTF than in normal everyday civilization.  You have the rule of law and its general deterrent to protect you if you use justified lethal force when civil order reigns.  As flawed as it is the criminal justice system in developed countries is at least sufficient to deter vigilantism.  You are likely to attract unchecked and undeterred vengeance from the associates of anyone you dispatch.  They may know where he/she was headed and never returned from.

Now, would I permit a scout to steal my survival equipment?  To leave having reconnoitered my equipment and stores, potentially to tell 15 people were they are located?  No.  Of course not.  I would detain the threat at the least and make an evaluation.  That's dangerous and probably not desirable.  A swift death is more likely for a trespasser.  Whatever the case I would be gone as would any sign of the body, before any reply to my acts was launched.

All this is a long way of saying that your survival rifle probably doesn't need 400-500 yard range.  Hitting uncooperative, moving targets at unknown distances over 200 meters is a tough thing for experts.

Rifle and Mobility:
Mobility and stealth (low footprint) are the Lone Actor's best (and maybe only) assets.  The three largest mobility limiters for a lone actor are food, water, weapon and ammo.  That said you need a lightweight, self-sustaining and self-contained weapons platform to complete your mission.  That mission being: Anti-personnel out to 100-150 meters and hunting out to, say, 300 meters.  You will be amazed how much of a difference half a pound makes over the course of a day.

Rifle and Combat Flexibility
Since you can't carry around an armory you need your survival rifle to do everything in your defensive requirements.  That really means CQB-150 meters for anti-personnel work.

Rifle and Durability
Simple.  That thing better not break.

Rifle and Maintenance
Simple again.  If it breaks, parts better be easy to find.

Rifle and Ammo
Never know when you might need to find/scrounge for ammo.  No stock, no matter how large, lasts forever.  SHTF means leaving caches around since you can't always carry it all.  Leaving caches means potentially losing caches to environment, memory, or enemy action.

All this tells me that a 14.5" or 16" AR platform is the best pick.

Shorter barrel for CQB and work from a Vehicle.  In my experience 16" works nicely for terminal performance and gets in and out of cars and other CQB situations nicely.  Some people like 14.5" but I think that the 1.5" difference isn't enough to change anything.  Add a 3x24 Compact ACOG with crosshair and you can put rounds on target out to 600 meters if you really must and can still do snapshots to the head at 5 meters without issue.

Lightweight itself and more ammo for the same weight than any of the 7.62 calibers.  8.5 pounds is 320 rounds of 5.56, 355 rounds of 5.45x39, 210 rounds of 7.62x39 and 160 of 7.62x51.  (See: The Maryland AR15 Shooters Site

I prefer HBARs because I like the durability side of the durability/weight tradeoff.  Also because I am prone to use barrel punches as part of my self-defense repertoire.  Some people prefer M4 but going down to fluted or superlight is a bad idea, I think.  AKs might beat out for durability and maintenance, but they can suffer for accuracy and "dems the breaks."

Can't beat ARs for parts availability right now (except maybe MAYBE with the M14/M1 platforms).  I keep a full parts kit with a spare bolt in a trapdoor grip and a full cleaning kit in the stock.  A lot has to go wrong with the weapon before I cannot repair it in the field.

Ammo.  I could go on for hours.  Suffice it to say that the 16" 1:9 will hurl 55 grain M193 out to 150 meters before it stops fragmenting and doing ouchies to badguys.  That's good because there is so much new M193 (sealed milspec ammo) around it's easy to store in bulk.  I have many thousands of rounds around in various places.  Plus, it's pretty hard to go somewhere and not find a sporting goods store with some .223.  That is, if the Zombies haven't moved in yet.

Let me know if any of this makes sense for you.  If not I can try to come up with other alternatives.

-Tatja