I was thinking about using a lower I had initially earmarked for 5.56x45 instead for 9mm. As I understand it I need to replace the hammer (cheap), buffer (cheap) and add a buffer spacer (cheap) and mag block (fairly expensive). I think thats the complete list other than adding a 9mm top end. My questions are:

Why is the mag block so expensive and how does it attach? What I dont want is a block that only allows mags in from the top.

Does the type of mag block dictate which magazine could be used? Im interested in using Uzi mags.

Whats involved w/ converting an Uzi mag to use w/ my AR? I figure its creating a new catch hole or modifying an existing one. If the former how accurate does the hole have to be? In other words can it be done at home w/ common tools and a simple jig?

For this conversion do I also need to replace the mag catch? It seems that adding the mag block would necessitate it.

Blocks run from about $100 to $200.  To me that isn't really all that expensive when you consider what other AR stuff can cost.  The blocks themselves have to either insert from the top or the bottom of the magwell.  Inserting one from the front back or side just isn't an option.  The mags will insert from the bottom, just like on a regular AR.  I am not aware of any blocks that require the mag to be inserted from the top.

For Uzi mags, you can use Hahn, RRA, ASA, or Garrison blocks (require modified Uzi mags), or the Hytech block (uses unmodified Uzi mags).  There are also other blocks for different mags.

Uzi mags need to have the notch at the back opened up and a new mag catch notch cut.  I did mine at home with a dremel.  Out of 15, I only had one (the first one) that gave me any problems.

No need to replace the mag catch.

tacked threads above should answer just about all you questions.

Quoted: tacked threads above should answer just about all you questions.

[/sarcasm on]Only a few hundred more informative posts like that and you'll hit 15,000!  WOOT!!!

Keep up the good work!!!!! [/sarcasm off]

Quoted: Blocks run from about $100 to $200.  To me that isn't really all that expensive when you consider what other AR stuff can cost.  The blocks themselves have to either insert from the top or the bottom of the magwell.  Inserting one from the front back or side just isn't an option.  The mags will insert from the bottom, just like on a regular AR.  I am not aware of any blocks that require the mag to be inserted from the top. For Uzi mags, you can use Hahn, RRA, ASA, or Garrison blocks (require modified Uzi mags), or the Hytech block (uses unmodified Uzi mags).  There are also other blocks for different mags. Uzi mags need to have the notch at the back opened up and a new mag catch notch cut.  I did mine at home with a dremel.  Out of 15, I only had one (the first one) that gave me any problems. No need to replace the mag catch.

What modification is done to the back of the uzi mags? I have a RRA 9mm and it came with two modified mags. I want to buy some mags and modify them myself and I know about having to cut the mag catch slot in them, but I didn't know I had to do anything to the back. I don't have any unmodified mags to compare to the RRA modifed mags.
Also how can the Hytech block use unmodified uzi mags if you have to do work on the back of the mags?

Thanks for any info in advance.

Compare an unmodified Uzi mag to your RRA modified ones and you will have an idea on how far you need to enlarge the notch on the back.  I just compared mine to my Colt mags.  The back of the Uzi mags has to be cut though so it doesn't hit the bolt catch.

The Hahn Precision website has a detailed drawing of the modifications needed for an Uzi mag to work.......look under the 'library' section.

Start off with good mags......there are some cheap ones on the market not worth the time.