Yup, Thorvikingpower shoots the matches. And I agree with what he is saying. You will see everything under the sun at a match. People will go with what they have or based on an idea of what the matches are. Once you've shot some matches, you get an idea of what works for you.
When you look at what the people going to the finale are using, there are some trends. Equipment is changing, and that makes sense. Equipment isn't issued and fixed, you choose it yourself, so why not customize it to something that works better? Precision rifles were traditional built and configured for prone shooting. But that doesn't make a lot of sense if most of your shots are not from prone. Barrels have changed from a preference towards MTU and M24 to Palma profiles and Sendero. Scopes have evolved and now we are seeing actions and stocks evolving as well. The barricade stop on the MPA is an example. I think that is just the tip of the iceberg....
To the original question; what weight? Well, it's a little more complicated than just a total weight. It's not just weight, it's balance. Balance isn't important if you're only shooting off the bipod or always putting the bipod on the barricade. But, once you start having to shoot in confined spaces, that's not always possible. Also doesn't work well when you put the rifle in a HOG saddle. And lets add positional shooting to that, with timings that don't allow you to sling in. A barrel heavy setup works against you when you start moving the balance point back.
This is how my rifle is configured:
That's isn't a HOG saddle, it's just sitting loosely on a U-shaped rest. But, it's perfectly balanced. I don't have to fight the barrel. The barrel is a 26" Medium Palma, but that alone isn't what balances it. Notice the black block under the cheek riser? It's made from carbon steel. Weighs about 2 1/4 lbs. That's right, I've added 2 1/4 lbs. to the rifle. And you know what? It makes it EASIER to shoot because it balances the rifle. Total weight is just over 18 lbs., but I'll take it over the 16 lbs. without the weight.
Few other things I've done to improve handling. Notice there are no butt spacer? Stock is as short as possible. And I'm 6'4"! Scope is also in a Badger cantilevered Unimount. What does this do for me? Well, it makes it easier to shoot positions with. When I shoot standing, I can keep my support arm perfectly vertical and lean it against my body. That means that I've achieved complete bone support. Don't need a sling or a bag to add mechanical support, the rifle balances itself on my hand right in front of the magazine. If I add a small weight to the back of the stock (small bag of shot), the rifle now balances on the mag. Ever see how Service Rifle shooters shoot an AR off their knee. I can do that too with my PR rifle. Again, no sling needed. Complete bone support achieved without one.