Not going to be wearing the holster in the jet, just when I'm on deck .... over a flight suit ...
In that case: try Cabella's for quick & easy shoulder holsters if you don't want to spend @ $130+ for a Galco Miami Classic or something similar ....
Leather M7/M9 Shoulder Holster $40


24 reviews ... 4.3 stars out of a possible 5. One review said: "Nice product. I found it to be very comfortable. It seems to hold a Colt Commander or a SIG 229 nicely. If your chest size is over 46", this holster will probably be too small for you. It would nice to see assembly instructions with pictures and more detail."
Another said: "I bought this holster to be used during my deployment to Iraq with the US Army. I am a military policeman and this holster really does the trick for my Beretta 92fs. Its been 2 months so far and no problems, great leather, great stain, and great stability. Buy it, you will love it, great piece of history."
Other offerings from Cabella's ... shoulder holsters
or 30 shoulder holsters from MidwayUSA for SIG's
or 27 shoulder holsters from Cheaper than Dirt for SIG's
I can't offer any personal recommendations as I don't carry a SIG.
