Could someone describe to me the function and effect of a forced rest trigger? I know there has been a big kerfuffle about them, but just haven't kept up on the AR side
There is a lever that gets pushed by the bolt carrier group as it travels, which pushes down on the rear of the trigger. Pushing down on the rear of the trigger forces the trigger forward against your trigger finger, resetting it so that it will shoot again. If you keep steady pressure to the rear with your finger, but not too much pressure, it will fire again, forcing a reset again, and so on until you stop applying pressure to the trigger or place too much pressure on the trigger, stopping the reset and stopping the gun from firing.
If you do not know what an AR15 trigger looks like when removed from the rifle (shame on you, disassemble that thing and look around, lol), then imagine a capital T. The bottom post of the T is where your finger is. The top bar of the T is inside the gun. If the gun's muzzle is pointing to the right, then the left side of the top bar on that T is the rear of the trigger. Imagine a lever pushing down on that top left side of the T, and you can see it would force the bottom post right, which means forward into your finger. It pushes forward until the trigger resets, ready to be pulled and fired again. You normally do this with any semiautomatic gun, rifle or pistol, by releasing the trigger, which lets it reset (do it slowly and you can feel and hear it "click" as the trigger resets - any gun, seriously, try it with your Glock) so that you can pull it again. The Forced Reset Trigger (FRT) simply pushes the trigger so that it resets while you are still pulling, without you needing to release. This results in your pull being made available very quickly as the bolt moves forward, stripping a bullet off the magazine, inserting it into the chamber, and resetting the trigger all in one movement. This means your trigger is pulling the trigger again probably a lot faster than you could do by releasing it and pulling again, and certainly more consistently. The speed it based on how quickly the bolt carrier group travels (and can be changed by changing gas, weight, and spring rates).
This is different from fully automatic fire in which you pull the trigger and the gun commences to firing and does not stop until you let go. The trigger never resets in a fully automatic weapon. The trigger functions only once, but a bunch of bullets are shot. It resets on a machinegun only when you release the trigger.
The frt is still semiautomatic fire because Congress defines a "machinegun" as a gun that shoots, automatically, more than one shot without manual reloading
by a single function of the trigger. Because the frt forces a reset with each shot, the trigger is functioning each and every shot, unlike the machinegun where the trigger functions only once.
Does that explanation make sense?
The Supreme Court in the
Cargill case struck down Trump's bump stock ban on the same statutory definition, finding that with a bump stock the trigger functions each (and every) shot. FRTs operate on a different principal from bump stocks, but the result in court would be the same because the trigger is functioning each time and not just a bunch of shots with a single function of the trigger.
Different federal district courts reached different results (no biggie as different district courts reached different results on bump stocks, too), but the Trump administration recently reached a settlement with Rare Breed Triggers, one of the originators of forced reset triggers, on litigation between Rare Breed and the ATF, and so the Trump administration will not be pursuing those cases anymore. This means that FRTs are no longer a "grey" area and you can purchase, possess, and use without legal consequence. (double-check your state law, though, as a few states have outlawed FRTs and bump stocks, e.g., Florida).
There are many versions of forced reset devices out there. Rare Breed, of course, but they have put a lot of their competition out of business with patent infringement lawsuits. One of the best right now for frt is the Arizona Regulator, already mentioned above by another forum member. It seems to function well in just about any decent mil-spec rifle without too much trouble.
There are lots of super safety designs out there, too, thanks to Hoffman basically releasing his designs (he is a young genius) out into the public without any licensing fees or anything, free for use. Several companies make kits with very high quality materials that last a long time. I use deeznutztactical <-- not a joke, lol. They make a quality kit. Rare Breed is also suing deeznutz, but I do not expect them to prevail because the designs are so vastly different.
If I were you, I would go to another forum, AR15 dot com and go to the AR15 section and then go to the Rate of Fire Triggers section. After about 3-4 hours of reading and going down the rabbit hole, you will have more of an education than you can get here, and be ready to select a quality unit.
Sorry for the lengthy post.