Perhaps this will head off some of the repetition in people asking "can I use this Glock (with these parts) at a match?"
The official GSSF rules can be found at the link below:
Or an updated version in the 2014 Vol II Glock Report:
In summary, GSSF requires that your gun be "stock" in that it cannot have any parts installed that were not made by Glock or that have been modified. The exceptions to this are:
any notch and post sights (including express sights, night sights, fiber optic, etc, as long as they're notch and post)
grip wraps/tape/panels or other grip enhancing materials that do not materially alter the firearm
slide and/or barrel stripping or refinishing
Pearce grip extenders on subcompacts
aftermarket non-metallic magazine basepads
Glock makes a flashlight that attaches to many of their pistols, but you can't use it or any other "barrel weight".
The above requirements for "stock" do not apply to the Unlimited division, where pretty much anything goes as long as the frame was made by Glock, safeties have not been disabled, you're firing a caliber for which Glock produces a firearm, and a shoulder stock has not been added.
The only "wiggle room" in the definition of stock is that GSSF doesn't, that I can see, define exactly what's meant by "modified". Common wisdom is that polishing (i.e. the trigger bar, connector, and any other metal fire control parts) is ok.
Grinding/cutting/drilling/changing the geometry of any parts is not.
Where is the line between polishing and grinding? A high speed rotary tool with a cotton polishing buff and the polishing compound of your choice will change the shape of a steel part if you work at it long enough.
Perhaps in a future version of the rules, this will be more clearly defined.
It should be noted, overdoing a polishing job or polishing the wrong places can cause a Glock to "double" or go full-auto. I didn't witness it, but heard that happened to at least one competitor at the 2015 Orlando match.
I witnessed it and it was not a pretty site. It was on the 5 to Glock Stage. IF you don't know what you are doing "Leave it alone!!!"