A fixed 10 round mag remove the rifle from the "feature" ban list.
A fixed mag is defined as ..."removal will require the use of a TOOL" Screw driver and a bullet is defined as a tool.
To build one you'll need:
Receiver wrench - (barrel vise would be nice)
Long 1/2" socket wrench with cheater bar
Go/No-Go gauge
solid vise on a solid bench.
Cliper would be useful to measure locking shoulder.
Scotch Tape
A way to drill and tap the mag release.
10 round mag
Stripper clip top cover
Check out FALFILE.Com for detail build instructions.
Parts kit come in different flavor of quality, and priced accordingly. STG are good kits, almost new condition most times (check DSA). You'll also need to get at least 6 (or 7 if have muzzle ) USA made parts. It is a Fed ATF reg.
Depending where you get your reciever - $240 - $450,
parts kit $200 - $400,
tools ~ $100
USA parts ~ $120
New Shoulder Lock maybe - $25
10 round mag - $15 - $30
DROS / dealer fee ~ 20 - 50
$700 - $1100.
Check Entreprise, sometimes they have whole gun sales...