Keep you stock waterproofed where it is cut away for the action, wood swells when it gets wet!! Also try not to allow water to get into the barrel as it can migrate into the compression chamber, when water and grease/ oil mix it can lower the flash point and cause dieseling on higher powered springers. If you spend a long time out in the rain/ high humidity your velocity can and will change, how much, it is hard to tell but high humid air does compress differently than dry air. For shirt periods of time usually not much change but, having spent many long days in inclement weather at FT matches...everyone had issues by the end of the day!!!