...please! :)

I guess this is probably the best place to put the "noob" questions. I've been doing as much reading and research as possible before jumping into this sickne...er..hobby, and I still can't find the meaning of these terms-

-What is meant by a "fence" on the lower reciever?

-What exactly is headspace?

-What is meant by high shelf and low shelf?

-And the bonus question...

Assuming the ban expires in 2004 and isn't renewed, will we be able to combine preban parts with postban receivers? This may affect how I plan to purchase items. I know, I know, nobody has to say it, none of the preban stuff will wind up attached to a postban reciever. I just want to know now because I'm not going to waste my money on a preban reciever/rifle if it's a moot point in a year.

Thanks for anyones help.

2) headspace is the dealing with the chamber and when a bullet sits in there.  Too much is bad, to little is also bad.  There are Headspace gauges that everyone should have.  a) GO gauge, b) NO-GO gauge & c) Field gauge.  It's good to have at least a GO & NO-GO.
IF the bolt closes on a go, then it's good and you good to GO.  If the bolt closes on a NO-GO then you'll want to try another bolt, if still closing on the NO-GO then the chamber is out of spec and a new barrel should be bought.  Do a search on Headspace, you might find more.  Gauges can be bought at [url]http://www.brownells.com[/url] or [url]http://www.bushmaster.com[/url]

3) High and Low shelf.  This is in the lower reciever toward the rear.  under where the take-down pin is.  In some newer recievers the shelf is high not allowing a [url=http://www.quarterbore.com/nfa/dias.html]RDIAS[/url] to fit.  A low shelf was the original mil.spec sizeing.

4) IF (and we all hope) the AWB will sunset there will not be any Pre or Post, every thing will be the same.  Thus all parts will just be parts, not pre or post.

Actually headspace refers to where the case is held in the chamber by the bolt or breach face.  Different firearms are headspaced differently.  Most pistol cases are head spaced on the mouth of the case at the forward edge of the chamber.  Bottle cases like the .223 are head spaced on the sholder of the case.   For these types of cartriges the head space is the position of a SAMMI spec case shoulder when held in the chamber by the bolt.

Edited to add that the fence is the ridges on the mag well.

The fence is the raise area on the front-right side of the receiver, around the magazine catch button and along the top of the lower, running forward.

I probably should have posted this with a new subject, but here goes anyway...
After reading the link for the RDIAS and DIAS and the following responses, am I to conclude that even the pre 1981 DIASs would be legal if the present ban sunsets?  If so, that would be yet another reason to call the senators and make sure this thing does sunset!!!  Also, how expensive are the M16 parts that would be required?  Probably just dreaming but this is interesting stuff.

No, the DIAS you mentioned would not be any more legal if the ban sunsets. Those were made prior to the 1986 Machine Gun Ban, and aren't covered by the 1994 Semi-Auto 'Assault Weapons' Ban.

RMK