FWIW, not much, about 35 years ago I fooled around with reduced noise .22s. At the time the well known choices were CCI CB caps and RWS cartridges that had no loose powder if their bullets were pulled. Both RWS loads were in very short copper cases. One had 17 grain round balls and other a 17 grain hollow base with a cone nose. Both would only dent fir 1x4 boards at 50 yards. What ever charge they had was underneath a paper wad that was stuck to the bottom of the case. Both of CCI's CB caps used a 29 grain .22 short bullet. One type used short cases, the other long cases. Both would go through a fir 1x4 board at 50 yards. Both were more accurate that the RWS cartridges in my rifles. The CB caps in long cases were a little more accurate than those in short cases. However, it turned out that the most accurate low power .22s were seldom discussed cartridges that are sold for another purpose, international rapid fire pistol matches like those in the Olympics. That's logical if you think about it. Olympians after gold medals need the best low power .22 shorts.