Not real sure what all parts you're using. But I guess if the ports line up within the comp it would work ok. But it does seem like a bit of overkill. Still it's a bit hard to picture exactly what you're doing … for me anyway...but then I'm easily confused ...

 

Sounds like a great way to convert your semi-automatic pistol into a single shot wonder.

 

If the barrel is ported, you already have the benefit of a comp. However, there are reasons to have ports and a comp if you are looking for almost no recoil effect and very flat shooting. It does take tuning of lots of things to accomplish this - overall weight, weight distribution, slide lightening, spring tuning, to name just a few.
The biggest rub is that you need a LOT of gas pressure to achieve this. So, 38 super can do this easily. Example one of my race guns had a 5 port comp and the slide was essentially stock. Even going to an 8# recoil spring, it would not function well. I cut two of the ports off the comp, cut two ports in the barrel (and milled the top of the slide flat and an exhaust for the two ports). Presto, worked like a charm. Just seems to float out there. So little recoil effect you barely need any grip at all.
But I wouldn't try this with a 9mm.

 

Hey bcd
A friend gave me a 9mm ported barrel(2holes ea. side) which I thought maybe could use on a 2 hole comp for extra effect. It seems like that would really work. Could possibly interfere with operation of the slide.
Appreciate your thoughts

 

If you can share a couple of pictures I might be able to give you a more informed opinion.
For example you say the ports are on the side? On the surface of that info, it makes little sense, unless they are like at the 10 and 2 o'clock positions maybe?
Also, is the barrel long enough that you can thread it for the comp? And it would need longer thread distance than is used for a suppressor (maybe).
So, a photo of the barrel showing those ports, and another with the barrel in the slide would be helpful.

 

It really depends on what you are shooting through the gun and how the porting is done.

The ports in the barrel will steal gas from the port baffles, and can make them useless. But if you have enough jetting gas everything will do something and it can be quite effective.

For USPSA open guns, you will see this exact thing done. The "ports" are usually referred to as popple holes. But moving from a setup with no popple holes to one with requires redeveloping your open gun load to something that makes bunch of gas.

THey are usually using 38 super or supercomp, but you see them on 9mm open guns.

Factory 9mm is likely not going to cut it. A lot of it isn't even going to efficiently drive a comp.

 

^^ This.
My point about not doing this with a 9mm. Even developing a major load would still be a heck of a challenge. You'd probably also need to shorten the slide or make other lightening cuts. Recoil spring weight would have to go way down, and then you have to modify magazine feed lips to assure consistent feeding with the reduced slide velocity. Oh, and as of shooting 9mm major loads in a stock SIG barrel, hope the insurance is paid up, 'cuz the risk factors increase exponentially.
So, yeah, don't do it. At least with the SIG configuration. Just my opinion.