BBs spiralling out of barrel

[Prisce]

A guy I play with has an M14(I don't know the make), he's fairly new to the wonderful world of Airsoft. He was playing with it today and half way during the day it stopped shooting perfectly and started to spiral out of the barrel.

Im talking 3ft spirals for about 20M and then flying off on any which direction it wanted.

As its new I advised he took it back to the shop to get them to look at it. But it got me thinking, what caused it?

My personal opinion (without taking it part) would be the bucking has split or moved severely causing the force pushing the BB to put severe side spin instead of top spin on it?

Any of you experienced techs had this before? Or any ideas what it could be.

This is purely because I'm interested in what it was, I'll probably find out next week  what the shop said!

 

[Lozart]

Gut feeling is that the hop rubber is split as you say.

 

[Samurai]

That, or some other obstruction in the barrel, I think.

 

[Hangtight]

Sounds like a combination of backspin combined with some axial spin. The only thing I can think of that might do that is a lump of grit or something in the barrel, probably near the muzzle.

 

[Prisce]

I thought this on site, but we cleaned his barrel on site with an alcohol wipe, and it still did it. 

Im still sure it is a split bucking, was wondering if you guys had seen the nozzle push the bucking and twist it to give this effect or something. 

What you guys say makes perfect sense and they were both my immediate thoughts.

Thanks for your opinions, I appreciate them.