I am wanting to build a rifle but have a couple of questions. I want my hunting rifle to be a .223 caliber. Do I need to buy a 223 lower or upper or both? To be a little more clear - I know that I need both parts for the rifle but does the caliber make a differance when buying these components and if so does it matter with both upper and lower or just one?
Is it cheaper to buy a complete upper and a complete lower or should I build one or both of these componnts? Also, is there any certian companies that I SHOULD STAY AWAY FROM? Please help a newby Harley

I'm not quite sure I understand exactly what you are asking, but I will try to help you out as best I can.  

Yes, the upper needs to be .223, or 5.56, or what is called a "Wylde" chamber.  For the differences on these, you can do a search for more details but a short answer is as follows: 5.56 is NATO/Military ammo and is loaded to higher pressures which benefits from the slightly more generous chamber on a 5.56 upper.  A 5.56 Upper will shoot .223 but is generally thought to be slightly less accurate due to the larger chamber.  A .223 upper will most likely not cycle 5.56 NATO loads reliably, but may have the potential to be more accurate due to tighter chamber tolerances.  The Wylde chamber, and I have no experience with these, is supposedly a compromise between the two and will fire and cycle 5.56 or .223.  

If you have no experience building rifles, or AR's specifically, and you don't want to learn, you can buy one complete.  Might not be a bad idea for your first AR.  You can learn about them, then build your next one.

Regarding the lower, same advice as far as building vs. buying a complete lower.  The lower needs to be for an AR-15 type rifle.

Hope that helps.

Thanks Jason, I really appreciate someone responding to my message.  It seems like there isn't many people in this forum willing to do this.

I didn't know if the upper is what dertermined the caliber or if it was the lower or both Do I need to specify a 223 upper and a 223 lower? So just to be clear. The upper is what determines the caliber of the rifle? The lower unit can be fitted to both calibers?

What is the price differance like between the 5.56 and the 223? Do they have varmint rounds for the 5.56?

I was in a gunshop this weekend looking for a 700BDL 22-250 and came across a bushmaster and I instantly fell in love with the AR 15 type rifle. I have never had anyexperiance with these type rifles but I know now that I have found a new interest. I am an avid hunter and own many rilfes from semi-auto carbines to bolt-action and even a couple of singleshots (ultra rifles). I have always done my own work on all of my firearms and really enjoy working and tinkering with them. After seeing this Bushmaster this weekend, I have decided to order all the parts this week and build me one (NOT BUSHMASTER PARTS TO MUCH $$$)). I found this site while doing some searching and have been doing some reading but it is all like foreign language to me. I don't know what I need other than I think it needs to be a flat top so I can mount a conventional scope and I would like a 20" barrel. I think I want the A2 butt stock and the regular pistol grip. Other than that, I have no idea what is a good CHEAP upper and lower that will be good to use as a hunting rilfe. SO, I am here hoping to get some help from the friendly forums of ar15 Thnaks for your help, it is very much appreciated.

You don't need to specify a .223 lower.   Just make sure you're buying an AR15 lower.

But you will need to make sure that the upper ( or barrel, if you're building)  has the correct chamber, Jasoncap gave a good quick rundown on the differences of the cartridges.  You should be able to get some more information with a couple of searches on the site.  Also check out the Ammo Oracle for allot more info.

CDKayak

If you are hellbent to build your own quickly, then I suggest picking up a Stag lower and a J&T or Model 1 Sales kit to assemble it.

If you don't mind spending some time doing research, then you can piece together exactly what you want and not have to end up with extra part.

From my understanding DO NOT fire  5.56mm in a .223 chamber. It  will overpressure the chamber.  Loers will work for .223 or 5.56mm or wylde .  Start reading threads and you will get a better idea.

I'm in a similar situation as Harley, I've been reading my butt off and can't really determine what I want to do. It seems that $$$ are not really that different between kits and puchasing halfs. Seems that the real advantage of building you own is that you get the exact rifle you want and don't spend the extra money and time swapping parts out after the fact.

I'm seeing about $100 jump from complete build to assembled halfs and again between halfs and a complete rifle.

Am I anywhere in the ballpark?

I saved about $100 building from parts as opposed to buying the comparable Rock River rifle.

I saved ONLY because I planned what I wanted and didn't let the "upgrades" get me.

I just didn't like alot of the "kits" because sometimes you get parts from manuf. A or sometimes Manuf B. I wanted to know where the parts were coming from and what kinf of QC they went through.

Of course it is a little different if you aren't betting your life on your rifle.

I have a Rock River Arms upper with the "wylde" chamber and it cycles 5.56mm and .223 rem great.

No problems with either. And both seem to be as accurate as the other.

thanks evryone for helping this newby out. I have been doing alot of reading but its confusing when you don't what evrything means or the differnce between an A2 or A4 or flattop. I will continue to read more and I hope to have some more specific questions for you all. I would really like to get into these rifles though I know once I do, I might as well sign over the house cause I won't have the money to make the house payment anymorehere
Anyways, thanks for all the help.

Harley

The lower has no idea and does not care what chambering the upper has.

It is not that big a deal shooting 5.56 in .223 uppers... I have done it quite a bit.  The rounds cycle fine and nothing has blown up.

The helps a bunh! I have done a lot of reading and never seen anything that said that but I have been wondering alot about that.

Harley