Speaking as an NRA Instructor with 21+ years of experience; as a former Law Enforcement Officer and as a former US Army Infantry Captain, Ill give you some feedback and you can take it or leave it.
First off, I wont even join a thread like this. You are going to get a ton of uninformed abeit will meaning replies.
Choosing a firearm is a lot like choosing a mate. Ya sorta gotta TOUCH them before you make a decision! So whatever advice you get, go to a gun show and FIND that exact model firearm and handle it! Trust me when you find THE ONE (not our Prez!) youll know it as surely as the Boy King drew Excalibur from the stone! Youre looking for that ineffable feel in your hand. How does it balance? Does it point naturally? Lay your finger along side the frame and POINT. Do you get the feeling that the barrel is aligned with your finger so that if you pulled the trigger the bullet would go near the point of your finger?
So Ill tell you what to absolutely avoid and a reason for that. Side by side or over/under shotgun: TWO SHOTS and very slow to reload under pressure.
Any PUMP action shotgun. Under extreme pressure, too easy to SHORT STROKE the reload in order to fire the second round. This means that there is a failure to bring the pump forcefully to the bottom of its cycle and then start back up to chamber the round. This results in a double feed jam and can only be cleared by a detail strip of the weapon (usually a gunsmith job) difficult to stay alive under these circumstances.
Here is what I recommend to paying clients (no charge to freepers like you) in the way of defensive firearms. All the way from handgun to shotgun to assault rifle.
I recommend to my clients (I just finished a consulting job in south Miami Dade for a guy who specializes in kidnap insurance in Latin America) a good semi auto with extended tube. Either the Benelli M2 or M4 or a tactical version of the Remington 1100 12 ga:
http://www.remington.com/products/firearms/shotguns/model_1100/model_1100_tactical.asp
Semi auto pistol is something that is reliable after firing an extended number of rounds without lubrication or cleaning and that lets out the majority of guns including the venerable 1911A1 Colt Government model. I can only suggest three brands: H&K, Glock and Sig Sauer. Caliber choice depends on your level of expertise, but I suggest either a 9mm or a 45acp. REMEMBER, bullet size does NOT "end the fight." Only shot placement does that! That's why both the British SAS and the FBI's famed Hostage Rescue Team used the Browning Hi-Power for a good many years. The SAS stuck with the 9mm and simply segued to the newer and proven Sig P226 while the FBI is still futzing around with calibers and makers. Not sure what they're currently using. Last I heard it was a Les Bauer custom 1911.
NOT the 40 because it offers a vicious barrel whip that will induce FLINCH and quikly start degrading accuracy. Thats what wins a gunfight, you know. ACCURACY under stress. Not caliber. 9mm is as small as I ever recommend and 45 is as big. I have used both. I do recommend that you use a DA first shot. Not a shot from the cocked and locked mode like you find on a 1911 Govt model. Its waaaay too easy to trip off the shot without being CERTAIN youre on target. You also have to remember to wipe off the safety and thats tough under life and death circumstances, especially as you age.
I carried a 1911 for 20 years both in the army and places I cant tell you about. But it was in a stupid IDPA ( I recommend you join: http://www.idpa.com) match several years ago that I lost precious time because my muscle memory failed me and I failed to wipe the safety off. If it had been real, Id have been dead. Now I know that MUSCLE MEMORY isn't unlimited. I went to a gun that didn't require that step for a very long time. However, recently the 1911 bug once again chomped on me and I decided it was simply time to REFRESH my "muscle memory." That just requires some practice. So, while I'm saving for the purchase of a new Sig Sauer C3, I'm doing exactly that. I'm practicing with IDPA and I'm carrying a 1911 once again to reinforce the need to keep a good mindset as a precursor to muscle memory. FOCUS is the key.
A revolver should be something you can hit with. Either from a range of 6 to 10 FEET from the hip (two handed grip, elbows locked into your sides) at rapid unaimed fire. OR at a greater range of 21 feet using the sights. 38sp or 357 magnum only unless you opt for the Taurus JUDGE with the 410 shotgun and 45 Colt caliber. I just bought one of those for trips out of town. Its a specialty gun for anti carjacking that I bought for my wife. Otherwise, I have everything I need. But certainly NOT everything I want!!! In a short barrel (3 or less) best to go with 38+P rather than 357 because the magnum will degrade in velocity so as to be less than optimal.
Assault Rifles:
STAY AWAY from the AK47 family in 7.62x39 cal. Yeah, its an awesome assault rifle. Designed to be cleaned in a muddy creek, shook dry and resumed firing by some little illiterate commie drone. The problem is the ammo. There are damned few makers in this country. Most is WARSAW PACT surplus and can be choked off much more easily.
You want to stay with a caliber that your own military and police forces use. That means NATO compliant. 5.56x45 and 7.62 x51 IOW 223 and 308 Winchester. I own an M1 Garand because the hunting aspect of the caliber makes it easy to come by everywhere and there are some specialty angles that are available to that round that are still LEGAL and decidedly not so to the other calibers. Remember the 30-06 was a US military round since the early 1900s. So it is still legal and possible to get ammo that is AP, API and most desirable of all APIT: Armor Piercing, Armor Piercing Incindiary and Armor Piercing Incindiary Tracer. Great for work on engine blocks and gas tanks. Plus the Garand is a very good (not perfect) battle rifle and of course if you run out of ammo there is that bayonet and club aspects available. Its heavy but I dont expect to hump it in any more jungle jaunts.
Stay with the AR platform because of its ease of maintenance, accuracy and caliber symbiosis. lol. Remember something else, youve got to have the WILL to win no matter how bad it all looks. Youve got to have the soul and mindset of a sheepdog:
http://www.gleamingedge.com/mirrors/onsheepwolvesandsheepdogs.html
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Saiga makes a "sport" version of the AK in .223. It's the best of both worlds.