I had one Crossman Skannaker that was a capable of competition accuracy. It was a bulk fill CO2 gun. The removable CO2 cylinders were filled from a bulk tank, and held enough for about 100 shots, but the pressure seemed to drop off after about 80 shots. It was fine for the 60 shot matches. I shot a couple of PTO matches with it and did as well as I was capable of, 530-540 on the 600 point match. This was back in the mid 80's when I could still hold a gun steady. If left and not used for awhile the seals tend to go bad and need replacing.
My current air gun is the IZH46,, single stroke pneumatic, and it is up to Olympic accuracy levels.