M4 - 2 port 4 port barrels

[Milspec]

I'm just trying to clarify.  When people talk about 2 port/4 port this is in reference to the gas ports in relation to the the pistons correct?

We're not talking about actual conventional porting which mitigates recoil/muzzle rise.  I searched for barrel picks to compare the two but I couldn't find anything on the interwebs.

[Vertigofirearms]

4 port barrels are exceedingly rare. I don't even know if they make them anymore.

[StrangerDanger]

Correct. When you look down the barrel of the current production M4, you will see two ports. One port for each ARGO plug. On the 4 port models, each ARGO plug had two ports about half an inch from each other. 
 

I haven’t seen one of these 4 port barrels in years. My burnt bronze M4 came with one when I bought it in 2004. It was the first release of the 11703 models with the neutered receiver extension. Within the first outing, I snapped a piston in half firing 2 3/4 buckshot. Took Benelli a month or more to send me a new piston after mailing them the broken one. 
 

Then for another 7000 rounds, the shotgun performed okay until I noticed that the bolt carrier was getting stuck when pulled to the rear of the receiver. Closer inspection found that the face of the bolt carrier was mushroomed where the pistons make contact. The carrier was so badly deformed that it was binding inside the receiver. The 4 port barrel was battering the carrier to death.

 

Trip back to Benelli at this point at my expense. Benelli replaced the entire bolt carrier group, barrel assembly, pistons, ARGO plugs, and handguards with 11707 model parts. 
 

Now at 17,000 rounds, no more issues have been encountered.