I didn't link from Brownell's. Must have been a different poster. I was referring to the shorter barrels, to you or somebody saying that the shorter barrels were somehow illegal. I have shopped Brownells, and they have good quality names, but usually you can get the exact same less expensive.
I am not and have not been in the market for a sear and other components to change my weapon to full auto or even 3 shot auto. It is another capability you only need if you are going to kick in doors, spray and pray, putting a lot of rounds in a small enclosed area. No matter how bad it gets, I am not going to have to do that. If spraying a silhouetted target at 200 meters you will probably miss a lot more than you will hit. I may not waste as many rounds downrange as fast, but I never miss at 200, even with iron sights. The probability of me, needing to engage past that is low, unless hunting or on the range practicing. If you got 30 guys, scared shitless, because they are being engaged by a machine gun and holding up their avenue of approach, OK. If all of them put a bunch of rounds downrange, they can definitely suppress or take it out. I don't do that anymore. I don't even teach it anymore, as I am retired. I sight, spotweld, aim, control my breathing and squeeze while holding on target. Modifying unless you have the proper credential is illegal and wasteful of ammo. I am paying about 52 cents a round. I can blow plenty of money on a Saturday without emptying 30 round magazines with 1 pull of the trigger. With 18 inch barrel and scope, i can reach out and touch the target while the spray and pray guy might not even scare the target if the target has been shot at before. I had a buddy, that set up a hillbilly range for paramilitary wannabe cowboys and there were a lot of full auto weapons. He put quarter pound sticks of TNT on a berm at maybe 50 meters, maybe less. He made a pile of cash selling ammo that day, and that was years ago when ammo was cheap. The people he had there were people that couldn't be trusted with a potato gun. I left, asking my onetime friend when he became such a fkup.