When you shoot at a match, most have some type of rules regarding what your rife can weigh to compete with the other shooters, so you need to be in the general weight of the other shooters ( I am at 22 lbs.). In general longer barrels will give greater velocity, with a slow to medium powder for the 6 mm. I have seen anywhere from 26 in to 34 in in length most barrels and they do not have a taper and are a straight blank, you can then cut off the ends to re-crown and re-chamber over the life of your barrel. The will veri some what for the 6 mm between 2650 to 2850 seem to be the correct velocity, now you can push the round faster and some do, but you burn more powder and barrel and recoil. Check with some local shooters at the next match in your area and see how they have their rifle set up. This will save you time and money when you build your rifle. Just a thought Savage make a nice factory target rife in 6 mm and it may fill your needs, I have seen how well they shoot right out the box.