How does the AR's forward assist work? I've never understood it.

The forward assistbutton  pushes a little claw into  notches in the side of the carrier which  push the carrier forward then it can engage the next notch if it needs to be pushed farther forward.

When is the assist necessary?

ensuring the bolt is in battery

one way to quietly load a round in the chamber

and for Those of us who are old timers:

[b]SPORTS[/b] (for malfunctions)

[b]S[/b]lap (bottome of the magazine)
[b]P[/b]ull (charging handle to the rear)
[b]O[/b]bserve (cartridge being extracted and next round is ready)
[b]R[/b]elease (charging handle)
[b]T[/b]ap (forward assist)
[b]S[/b]queeze (trigger)

In theory it was for when the gun was heavily fouled since the charging handle design doesnt allow you to force the bolt home.  In practice, the only time I ever use it is when Im verifying the chamber's loaded condition just to make sure its fully locked.

Some guys, myself included, tap the FA after we charge the weapon just as a precautionary measure.

I always thought SPORTS stood for
Scream
Panic
Overreact
Run
Throw down your weapon
Surrender

Maybe that's just in France.

Never

I have seen comments on this board and others deriding the forward assist feature as useless and dangerous.  The usual objection goes something like this "if a round won't chamber because of fouling, you probably don't want to force it into the chamber anyway, since it might damage the weapon or cause excessive pressure".  This assumes the the only reason a bolt doesn't reach battery is because of chamber fouling.  It is much more likely that fouling or foreign matter (sand, dirt, etc) will accumulate in the upper receiver around the bolt carrier and cause the bolt to stop prematurely due to friction and or obstruction.  In this case a firm rap on the forward assist will bring the rifle into battery and allow the weapon to be fired.  I personally wouldn't own a weapon that didn't allow me to positively insure bolt lock-up.  It is like an emergency brake on a car.  You don't always use it, but when you need it - you REALLY need it.

2IDdoc - THAT was hilarious!

I use mine constantly, its only been needed a couple of times, but I thumb it constantly.

The idea that you should never use the forward assist because if the round doesn't chamber you probably don't want to shoot it anyway is a valid point for range shooting. However, if you are not range shooting, you might HAVE to use the forward assist to chamber a round because you are shooting for your life. I seriously doubt that I would ever be in that situation, but it is nice to know it is there if needed.
You can't always just stop shooting and sort out the problem. One option of course is to simply run the action and eject the offending round. But what if the next round does the same thing ?
When I was in the military, I had to use the forward assist a number of times in training (never served in combat). I suppose I could have just said that my rifle was malfunctioning because there was sand in the action, but, you fight as you train, so I just hit the forward assist and kept firing.
It is also nice to know that the bolt is fully forward when you load the rifle. I think it is a good habit to get in to. And, as was already mentioned, it is a nice feature when you are press checking to ensure that a round is chambered. When you pull the bolt back 1/2" or so, the bolt doesn't always seat fully when  you let it go. A tap on the forward assist give you the peace of mind that the weapon is ready to go.

I can tell by sound if the bolt seats properly or not.
If I need to push the bolt into battery,
I just push on the dished-out portion of the
bolt carrier.

Never had a rifle witha F/A and never will.
They are not needed.

I wish some one could prove this definatively one way or another.

It would make the AR upper much lighter and cheeper to make if the FA could be eliminated.

My HK91 &FAL don't have the charging handles connected directly to the bolt & I have never had them not go into battery before.Millions of these rifles in their military form have seen use around the world, although Israel did fit forward assists to their FAL's.

I have seen rifles locked up non-functional because the forward assist allowed the rifle to partially lock closed just enough to not allow it to fire and make it damn near impossible to extract.  

If there is crap in the chamber, remove the mag, point weapon up and down, cycle weapon a couple of times and then blow the loosened crap off of the bolt face.

The FA is no good in this scenario and will anot allow you to re-size an oversized round either.

True Story.

Soldier is in combat. As he is running, he trips and as murphy would have it he lands in sand, basically he needed tear down and clean in a battle. No thime for that. With the FA he was able to have a single shot weapon. Though he was not as effective as his comrades he was still in the game.

Who knows that guy in Iraq that was single shooting his weapon coud of been doing the same thing.

I treat it like 4 wheel drive. I really never use it, but it is good to have if you need it.

GG