What is the difference between a full auto carrier- bcg and semi auto. I need to get one and am looking at some but does it really matter for an ar15?

Full auto is not cut on the bottom so that it trips the sear.

It does not matter what you use in your AR, more of a personal preference

Thanks. Very good illustration.

I have the M16 bolt. Do any of these have an advantage over the other? Other than the ability to go full auto.

Some say the cutout carriers are tough on firing pins. I haven't found that to be the case. These days, get the one you can find at a reasonable price.

It doesn't have the ability to go full auto.  It's simply supplied as designed by Eugene Stoner.  It's called the full auto or m16 carrier simply because for a long time that was the only place you could find them in. A semi carrier is a design compromise used to lessen the liability for manufacturers.  Semi carriers run just fine in full auto with a registered legal lightning link

This is why they are legal. They have nothing to do with full auto by them selves. As in a full weight (what I call your full auto carrier) is used to fire the gun in any configuration. An auto sear as a example is only used to fire in auto.  It's like saying a gun is full auto becaus they barrel is capable of firing full auto. Sure it is but that means nothing.

It's the lower and the FCG that dictate full auto.

I think some people overthink this. Maybe they do notice a difference in a semi-auto as far as functioning (with their particular setup), but I don't. I generally use FA carriers, but I put a SA BCG in my son's new rifle and it runs perfectly (16" mid.)

As long as it's a good brand, get/use what's available right now.

That's the only place they will work and function in full auto also.  If you have a registered receiver with the 3rd hole and auto sear, you would absolutely HAVE to have the M16 (full auto) carrier for the full auto to work.  On a semi-auto carrier the bottom cutout on the carrier prevents the BCG from being able to trip the auto sear to release the hammer.  (Not entirely sure on the DIAS, never really looked at one or handled one, but I'm assuming it functions the same as a standard auto sear.)

I never claimed it had the ability to go full auto by itself. I was asking if one had an advantage over the other. "Other than the ability to go full auto (with the right components)".

I have read, and listened to opinions on both sides.  This topic will never have an end.  I have played with; and own both styles.  I have 14.5" rifles in midlength and carbine, and I have 16" rifles in midlength and carbine.

I mention this because the only difference I notice with the 2 styles of BCG (all of mine are top quality BCGs) is that in a carbine, expecially the 16", the extra weight makes it a bit smoother to shoot.  Having said that, I can add an H buffer, switch back to the SA, and achieve the same thing.  The 16" carbine is obviously a bit overgassed, so this is a bandaid.  

My midlength rifles could care less.  With a carbine buffer, I notice no difference at all.  I haven't done extensive testing, as swapping bolts in and out of carriers tends to eat up my range time.

In short, it seems to me that the felt recoil, or comfort in my carbine gas rifles is the only significant difference.  I do run FA BCGs in all of my 5.56 rifles, now.  I have SA as spare..  I recently moved one of those WMD super whiz bang BCGs in place of one of my DD SA units.  Hoping that was not a mistake.

I wish I knew for certain that one was better, but I don't.  Arfcom says run the full auto, so you must assimilate, or be destroyed

Incorrect. Lightning links require the SP1 carrier, not the semi auto carrier.
Colt later went so far as to remove the bottom completely to prevent any FA use. Google colt half circle or half moon.
Correct about DIAS. They require full m16 parts kit minus the regular sear.

About 1/2 oz.

Which is the reason most "experts" recommend them. The extra weight is said to enhance reliability.