Got around to trying how this launcher would work in a big bore version. This was accomplished by simply replacing the barrel with a 1 inch pipe. Had a truly wicked projectile ready for the purpose, good weight tipped with a broad head. The 500 grain plus dart had plenty of performance, 320 fps generating over 165 joules of energy. Quite comparable to most crossbows on the market. A mark 2 launcher optimized for heavy ammo should have no problem putting out 200 joules plus.
A very interesting discovery was how much temperature affected the performance of this launcher. After a very warm autumn, today was over 12 degrees cooler. Speed was down by a good 10 percent for all ammo at any pressures. Could not get near the speeds tested in warmer weather. This is very minor effect in high pressure air rifles, but the very low pressure of my launcher must magnify the problem.