What ammos that with buddy? Might try that taper myself
Up to 12mm lead mate.
If your tapers are too large for the ammo weight you are shooting you will lose speed. For 18mm lead I would try 23mm-18mm to 25mm-20mm. Anything over a 25mm taper I have found overkill with doubles, unless you are firing canon balls or are using an extreme taper which I wouldn't recommend due to the short band life, especially now the weathers dropped in temperature.