Dreuf is right! That is why it is not connecting."dreuf"If you need to get it perfectly centred :
1) remove the stock
2) unscrew the bottle
3) unscrew a bit he foster fitting until it is perfectly centred
it is fixed
Hope it helps
If you have a regulator you need to bleed the regulated pressure inside the action too, keep that in mind. The screw that secures the stock to the action is a bleeding screw that goes all the way to the regulator chamber, by just unscrew that one the air will come out and you will be able to twist the foster. If you don't have a reg this step is not necessary. Cheers"dreuf"If you need to get it perfectly centred :
1) remove the stock
2) unscrew the bottle
3) unscrew a bit he foster fitting until it is perfectly centred
it is fixed
Hope it helps