I'm pretty new dealing with Ar's and I'm going to build my own. Now I'm not talking about from a bunch of pieces I'm talking about buy the lower then the upper and be done with it. However Something I don't know about is say I buy a Mega Lower, Will it be registered? I just don't understand the rules following it. please inlighten me Jerad

The lower is the serial numbered part, so in the eyes of the law, the lower is the firearm.  Therefore, any lower you buy (unless it is a direct in-state purchase from another person which is allowed in many states) is going to be registered and a 4473 will need to be filled out on it like any other firearm.  The lower parts kit, buttstock and kit, and upper end are not firearms so those parts will not need to be transferred through an FFL and you can buy them direct from any number of sources.
 Do not get tricked into paying more for a so-called pre-ban lower.  The law states that regardless of when the lower was made, if it was not assembled into a pre-ban configured complete rifle before Sept 12, 1994, it cannot be assembled now into a pre-ban configuration.

Ok thanks for clearing that up, I now have a much better understanding and I've been doing alot of reading about tooling your own 80's. My questions are these:

When you buy a Bushmaster or Colt what type of metal do they use and is it cast or forged?

Also Where is a good place to get a forged lower and is it worth the xtra $?

I'm sure I'll have more later but this is it for now:)

According to Bushmaster's website, they use 7075 T6 Aluminum Alloy Forging.  I couldn't find what metal Colt uses, but I'm pretty certain it is the same.  Both are forged receivers.

To get a lower receiver, check out [url]www.quanticoarms[/url].  They have Eagle Arms (Armalite) lowers for $85!!!
[url]http://www.quanticoarms.com/asp/itemDetail.asp?dispItemNum=739&type=M&CMN=Eagle Arms&CMNum=22&CMSNum=68&CMSN=Receivers[/url]

You could also do a search on the EE for "Iblis".  He has the stripped MEGA lowers for $99, but I thought they were about $85 or so a while back.

I have one rifle with each lower and they are high quality lowers.  You would not go wrong with either one of them.

Also, forged are much better than the cast lowers and well worth the slightly extra money.  The cast lowers are more prone to breakage than are the forged units.  On the thread "I crushed an AR today" on the main AR discussion board, the man mentioned that it was a cast lower he crushed and it just crumbled.  If you were to, let's say, break down the weapon by pulling the rear break down pin and the upper got away from you as it fell open, the cast uppers are much more likely to snap off the pivot pin holes than would a forged.  Now, you are not supposed to let the upper swing down like that anyway, but as we all know, stuff happens.  The forged lower is much more likely to let you get away with an oh-oh like that once, but the cast is likely to send you to the store for a new lower.  Like they say, spend a little more now or a lot more later.  Go with the forged.  

Well I would really like to build one my self, as it would be legally unregistered. Is there anyone that will sell a forged lower that is ready to be placed in the jig and drilled/tapped? I certainly don't mind paying the xtra money for the stronger receiver, however if you don't have access to a mill it sounds like the only thing you can do is go cast, well it also sounds like cast sucks. I need some advice, because if I do decide to start buying and building lowers I’ll have to invest a lot of money into tools and I don't want to make a bunch of receivers that will crack, break, or fall apart.

TTT The help has been helpful, but I need these questions answered:

Well I would really like to build one my self, as it would be legally unregistered. Is there anyone that will sell a forged lower that is ready to be placed in the jig and drilled/tapped?

I certainly don't mind paying the xtra money for the stronger receiver, however if you don't have access to a mill and it sounds like the only thing you can do is go cast, well it also sounds like cast sucks. I need some advice, because if I do decide to start buying and building lowers I’ll have to invest a lot of money into tools and I don't want to make a bunch of receivers that will crack, break, or fall apart.

thanks guys

[url]http://www.ktordnance.com/kto/products.php[/url] has 80% lowers.  You may also want to look on Ebay.  There are people selling the 80% lowers on there all the time.