Let me see if I have this straight.
A Full auto BCG is stronger and more durable in a  semi auto M4 set up than a semi auto BCG?
A Full auto BCG is totally leagal to own and use without any paperwork?
A Full auto BCG will work with the Buffer set up that's already in a semi auto M-4?
The gun will kick less with a Full auto BCG?

1. Doesn't matter
2. No papers
3. Yes
4. This is subjective

1.  There is more material in the BCG...less is machined away...particularly at the rear.
2.  It is just a part.
3.  Uh huh
4.  Who thinks a 5.56 kicks anyhow?  

kick? Seriously?

forgive my retarded-ness but what is a BCG?

Wouldn't the full auto BCG 'kick' a little more due to its mass?  If you could consider any 5.56 AR recoil 'kick'.

If you use an M16 carrier and a heavy buffer, you might find your carbine choking on 50-55 grain ammo.
This set-up works best with 62 to 77 grain bullets.

If you mainly shoot 50-55 grain ammo you might find a shrouded AR15 carrier and a standard  CAR buffer will work just fine

I use shrouded AR15 carriers and rifle buffers in full length rifles, shrouded AR15 carriers and H buffers in M4 carbines and M16 carriers with rifle or H buffers depending on the stock assembly used in tactical Match and Target Match rifles using heavy bullet loads.

No. (not enough that you would ever notice, anyway.)

Yes.

Yes.

No. (not enough that you would ever notice, anyway.)

No because its moving slower, so the actual recoil is the same, but the energy is more absorbed by the spring and the felt recoil is longer, but the spike at the end (when the buffer hits the back of the reciever extension tube) is less because the BCG has less potential energy.  a light buffer and BCG move back really fast and have more kinetic energy when it hits the back of the tube giving you more felt recoil.  It works like a recoil pad, they dont remove energy(since that is impossible/impractical) they just cause the energy transfer into your shoulder to take longer and hence less energy per unit time.  If the heavier BCG was moving at the same velocity as a lighter one then yes, there would be more recoil, but this is not the case.

for the OP they are more durable and reduce recoil and are legal, but for practical purposes its not enough to matter since most semi BCG last a lifetime and recoil reduction is negligable.