Colt has never been civilian friendly since I became gay for colt ARs in the 1980s. Always been told that Colt did a lot to keep full auto out of civilian hands and for some stupid reason doing that would enhance there chances to get government contracts. I've known several NFA dealers back in the day and all of them did not like to deal with Colt. Having said that I have a converted SP1 big hole lower and 5 big hole uppers for it to have variety in the upper I shoot, I do not like those adaptors you asked about, they will work but a little agravating to use. I also have alot of colt AR 15s put up just for the heck of it.