Obviously I know that .357 .38 aren't rifle calibers, I just use that as an example because I know that a pistol billed as a .357 can fire .38 but not the other way around...

There IS a difference between .223rem and 5.56 NATO, a quick google search will give you a plethora of articles explaining the difference. From my understanding 5.56 NATO does produce higher pressures in the chamber than .223rem. That being said, most AR varients will run both .223Rem and 5.56 with no issues. I've ran 1000s of rounds of each through my RRA AR-15 and never had a problem.

.38 and .357 are dimensionally different cartridges (rounds).A 357 is too long to fit in a .38 revolvers cylinder .223 and 5.56 NATO are dimensionally the same round that's the difference.

Thats pretty much what I am wondering due to the fact it is such an old model... This thing is probably early 80's at its youngest... Also, as with any rifle, I wonder about seals and gaskets and what-not... I know the springs have been replaced recently, not too sure about anything else...

What's the barrel marked? U can shoot .223 and 5.56 in a 5.56 barrel. Do Not shoot 5.56 in a .223 barrel!!!!!

http://youtu.be/juUJdzFFORs

This one is mobile!!

So there is a marking on the barrel that should tell me this? Thanks Justin this is the answer I am looking for... Where is this marking typically located?

If the barrel doesn't say 5.56 is it just a simple matter of changing out the barrel to make it into a 5.56 or is there more to it then that?

Can you elaborate on this?

Typically it's marked between the front sight and flash hider in that area but could be on the underside. If not, remove the handguards and look at the rest of the barrel. Something like
Image

5.56 barrel/chamber has more of a leade vs 223. It's has something to do with the pressures.
http://www.thegunzone.com/556v223.html

Rob, granted most ammo u will find will be .223 anyway

Thanks... :-) I'll have my Pop's take a look and see what he got... He bought it from a friend for 400.00 either way its a decent deal I'd say...

Next question... My dad has it in his head that it is worth more because it is the original civilian version made by Colt... is this true? Does it need to be kept as is or is there no harm in modifying it? He seems to think this Triangular handguard is something special... other then making it look older I don't see anything special about it...

I would say its possibly worth more depending. Best bet would be to ask over on ar15.com and post good pictures of the rifle and the markings on the lower receiver. Or send me the pix and ill ask

I'll definitely take you up on this... It might be a month or 2 before I see him again and can take pictures but I'll definitely send em your way.... I just wanna know if it was a decent deal for my Pop's and if this rifle is better left as a dinosaur or if I should mod it out...

Thanks Justin... :-)

sounds like a good deal to me.

The caliber will also be located on the bottom half of the rifle on the side of the magazine well, IF the rifle is 100% original parts from the factory. If someone changed out the barrel at a later date, then the markings on the side oft he mag well don't mean anything.

Now, depending on how far back that AR dates, it is worth considerably more than $400, even before all this craziness started. Honestly, you need to ask the guys at ar15.com, but I'll take a stab at what I remember.

The original Colt AR lower had a design "flaw" that made it super easy to convert to full auto. These are commonly referred to as "preban" AR's. Bearing in mind that I don't know jack, there is a decent chance that the AR your dad picked up is one of those. If so, then you would have the most value in selling it as is to a collector and buying yourself a tricked out new AR :-)

BTW, ALL of the preban lowers I'm looking at right now in the gunbroker.com history all are marked .223 caliber, so I'd stay away from 5.56 ammo for now.
ALL of the preban AR's I'm looking at also have a round handguard, even the one dated all the way back to 1977, so like I said, you're really going to have to post pictures for the ar15.com guys that know their stuff in order to correctly ID it. But I definitely wouldn't do anything to it until then.

Definitely won't, all we have done to it so far is give it a good field-strip cleaning and put a few .223 rounds through it... I will get all sort of pictures of it when I go visit next time... It was a PD- swat weapon from early 80's if the story is correct... he let it go for so cheap because he was hurting for money... This was a few months ago but my Dad just showed it to me recently... I bet he is kicking himself in the ass right now... :-)

Another reason I ask is because I am left handed and I want a Left-handed AR... from what I understand this one is either not convertible or is to valuable as-is to convert for my left-handedness... All I know is that it feels like a toy shooting .223 through it... I am pretty sure a 9mm has more kick...:-)

It does give you the option of using different uppers by not choosing a dedicated lower receiver.

My RRA 9mm uses a magblock, made by rock river, that uses colt style magazines. I can remove the magblock and go back to .223 or even 22 and whatever in between. The only reason that I would like a dedicated lower for Glocks, is I have a crap ton of Glock mags and when going to the range I can shoot both the Glock and the carbine without having to carry extra mags. Plus I believe they may be offering .40 and 357sig too.

If you want to try an AR-22, I can let you try one of those out as well :-)

Thanks the input and offer Greg. I was planning to get a .22 AR until I found out about the pistol caliber rifles. Either way, it'll be hard to find any 9mm and larger carbines with the frenzy going on now.

Even more mobile...

http://www.youtube.com/watch?v=O_lnq0HYBQE

Dare I say the ultimate in home defense?