I am not an in-line shooter, but in the traditional rifles, hang fires occur for a number of reasons. The big one is there is some substance be it, water, oil, greese, fouling, or burnt powder in the nipple port area. The other is there are good caps and then there are rotten caps. Another cause is, when you swab the barrel during shooting, you push stuff infront of where the spark comes through. Or there is moisture in the barrel when you load it.

To reduce the chance of that happening, first off, even an in line, pop two caps off before you load your rifle for the day. This will char the spark channel and blow out anything that might be in there. I always make sure the barrel is wiped out with a dry patch or two. I do not want to push any oil that might be on the inside of the barrel down to the nipple area when I load it for the first time. I realize some people have a fowling barrel issue or an oiled barrel issue. I like a clean barrel. After the rifle is loaded, take your nipple pick and push it through the nipple into the powder charge, although with pellets that might be a hard thing to do. Last is, make sure you have a tight fitting cap and it is seated properly on the nipple.

You might want to inspect your pellets and see if they look bad. I am not really sure what to look for in that respect. If the powder got damp, you can definately get a hang fire. If I had an inline, I would use the loose powder. Make sure you load the pellets properly. There is one end that has black powder on it, so I have been told.

I shot my sidelock on the range and it functioned fine in the damp air until I had fired the 12th shot (without swabbing I might add... forgot my patches and alcohol). Then we got a hang fire and stopped with the rifle for the day.