Reply To: Why does the POI change with a Moderator on?

Forums Field Target Field Target Talk Why does the POI change with a Moderator on? Reply To: Why does the POI change with a Moderator on?

Link

fe7565
Participant
Member

@i_like_irons :

“The only time a moderator would not affect the point of impact (due to barrel harmonics) is if it were a shroud that was part of the breach and the barrel makes no contact what-so-ever with the shroud.  The inherent problem with such a design would be that the baffles would have to have a large enough hole so that you don’t get baffle strikes.  That would make the thing a bit louder. ”

This a very interesting point. My Daystate Airwolf MVT’s 17in barrel has a fork that slides over its end inside the shroud. Then an air stipper/chrono combo follows that which also acts as a moderator. The shroud is held on the barrel by two allen screws. The breech end of the shroud fits up snug against the breech body, it may or may not touch it, or may touch it partially. So my barrel/shroud combo may or may not be “free floating”.  My .22 MVT “kicks” a lot more than my .25 Vulcan. I can see that during the firing in my scope-view. The MVT kicks higher and takes longer to settle down after each shot. I suspect that the barre;/shroud combo may flex during each shot where the shroud may or may not touch the breech.  If it touches the breech that may affect each shot. So I moved the shroud a bit away from the breech, about the width of two sheets of paper. Will see next time I take it out to the range.  But that’s barrel harmonics.

Still, I think that all those internal stuff inside the shroud can affect the pellet as long as such high pressure air is behind it.  Some with the Vulcan added some 1mm to 1.5mm holes near the end of their shroud that allowed some of the air that built up inside the shroud (to be later dissipated towards the front) instead to dissipate towards the rear. I think the Airwolf MVT may benefit from this also, albeit the rear of the shroud near the breech does not have any o-rings so it’s not sealed towards the rear.

Stock photo of an Airwolf (not MVT) front with shroud removed and an MVT shroud where it meets the breech: