I've seen similar. My guess is that the plastic eccentricity from the shot tube can "point" / deflect the shot tube to point a slightly different direction--resulting in different zeros. In ours, I scribe a white paint mark across the barrel and tube. Then only screw it back to where the lines match. I have also found that cleaning the shot tube contributes a great deal to accuracy. For many years, we have cleaned with lighter fluid and a cleaning felt--the lighter fluid because it 100% evaporates, but the oil draws out quite a bit of muck. Technically, a BB transiting the barrel is an air bearing--ideally with a small cushion of air continually surrounding the BB with most of the air pushing the BB, but a small portion of the air leaking around the perimeter of the BB. To avoid inducing a spin or a bounce on the wall near the muzzle, the most important aspect is likely how uniformly round the BB is.

Do you think a model 25 shottube can fit in it? My friend bought one and when he found out it was a single shot muzzleloader he was very upset but doesn't want to spend any more money than he has to.

Now, I want a 5 page essay on what you did wrong.

@@calebschank8105 best I can do is one because the other four burned

I will except that, but no double spacing

@@calebschank8105 will you take hand written?

Because it takes more effort and has more heart put it, I will make a single exception to the rules.