colt makes thiers with the "das" filled in its called a sear block.
colt also made thier trigger parts "oversized" to prevent tampering.
bushmaster will take a "RDIAS" with no machinging I belive,.,
the Registered "lighting links" were originally for the colt SP1..
tempeing with an AR15 to make it full or busrt is not worth it..
here are your options.. :
1 cheao way .. learn to bumb fire,....
2.. save up sell you left nut and get a regestiered rec. a RDIAS or a "LL"..
wanna see the paper work for transfering a class III weapon go to
www.tittleII.com
form one to make a firearm and silencers
form 4 for machine guns... give the ATF $200 for a stamp wait about 6 months < if your lucky> and presto your a legall machie gun onwer.