Roadblock

Looks like I have 4 ports, not 3. Cane someone give me the size for a 4 port barrel? Also what size drill bit?

Unfortunately I'm not sure I'm any more ahead then before I asked the question. I'm almost more confused now I think! I don't think I'm going to give up on the S-12 yet but I think I want to pick up a good ol Remington 870 Express too!

After some careful examination, I've learned that I actually have four (4) ports in my barrel. I can not actually see one of them from the gas block BUT if I shine my 300 lumen Surefire LED light down the barrel from the threaded end and look into the gas regulator, I can clearly see 4 points of light shining. They are in a diamond formation with one at the back, two to the sides and one in the forward most position of the formation. The one forward most seems to be JUST either under or right on the edge of the gas blocks large hole because I could not see it without light shining threw it.

First off I want to say thank you for the replies. Also I have been doing a TON of reading here which was why I posted my questions. This is my first shotgun. When I say first shotgun, I mean FIRST shotgun! Picked a hell of a shotgun to learn on huh? =) I've big into 1911's and AR-15's. I've never bought a off the shelf AR before, I've always build my own. I've also re-worked all of my 1911's and build two of them from bare Wilson Combat frames and slides. I like to tinker. I've also done a conversion on an HK USC to UMP and a SL8 to G36K. Funny story, I went clay shooting about a

Just picked up a S-12 Sporter. Just finished my conversion. Bought some Herters 2 3/4 7 1/2 target loads which are low brass and it will not cycles on the number 1 or number 2 positions. So far all I had done was add the C.S.S. piston to the gas system. My understanding is that this is somewhat normal. Some people report they have S-12's and never had any issues but it sounds like the majority do? I saw the thread about opening up the gas block to more of a D shape if the ports were obstructed. Well, I can actually see all 3 ports OK'ish when taking the regulator plug out but it's