Sig 556 Port sizes

[Crowmosly]

So I've been working on adding settings and tuning my Sig patrol swat and wanted to let the other 556 owners know the results of the port size testing.

I've ground in 6 total settings to the gas block. The original port into the piston was around .40 with a .42 or something out port. Which the out port basically has no effect on the cycling at all by the way so don't enlarge your factory out port. DON'T DO IT!...lol.

I just tested the first setting and progressively larger bits. I am using no out port at all for these. Keep in mind mine is the patrol length probably take larger bits for a full length system.

.025 #72 Came back far enough to get the shell out of the chamber and stop.
.028 #69 Eject case almost straight forward about 4 feet and didn't chamber the next round.
.032 #67 Ejected 12 feet at a 45 degree angle.

Case damage is reduced big time. It now leaves two very light dents one midway down the case, and on the bottom of the case rim. Normally these dents are big... the rim dent actually makes the cases very hard to fit in a shellholder. It use to eject 30 feet...

 

[seurto]

thanks for the posting. Would you be interested in doing this for others, with Sigs? lol

 

[Fyrtwuck]

Is case damage the only reason you're making these changes? How badly are they getting damaged?

 

[Crowmosly]

Uuuuum... I could... but I would suggest doing it yourself... I wouldn't want to be liable for breaking a part that super hard to find... All you need to do it is a dremel, drill and a $9.99 set of little tiny drill bits. (amazon.com)

As for the cases they were really tough to get in & out of shellholder. And it put big dents in the side of the case. Some the case neck is smashed in. Plus it threw them 30+ feet, making them hard to find.

 

[Fyrtwuck]

Is there any kind of ejection port buffer for this type of rifle?

 

[Crowmosly]

Nope... some people place a piece of velcro outside the ejection port. I kinda like the scar the brass leaves on the side really. Just hated how it dented brass.

 

[seurto]

lol, appreciate it.. Lemme ask you, how are you keeping the port that you want lined up? Are you also creating indents on the selector (is that what you mean by "ground in"?

I'm gonna have to break mine down again and take a look to get a better idea of everything..

 

[Crowmosly]

The best way to determine where to drill is dremel in the detent where you want it. Then clean as much carbon off the outside of the valve as you can. Then place the rifle on that middle setting or wherever the detent is and fire about 5 or 6 rounds. It will fire in single shot.

The firing will place a perfect carbon spot where the port is so you can drill it precisely. There is some room for error. The port from the barrel is fairly large.