There are a lot of 'toy' paintball guns that use the .5 cals.
The best are the .43 at 400 FPS like the Rap4 Xpower which is incredibly accurate and has a very flat trajectory as used by the military.
but they're not legal in the UK so you are stuck at 300 fps and I assume that .68 was picked because it has a greater surface area for the air to push against.
The best are the .43 at 400 FPS like the Rap4 Xpower which is incredibly accurate and has a very flat trajectory as used by the military.
but they're not legal in the UK so you are stuck at 300 fps and I assume that .68 was picked because it has a greater surface area for the air to push against.