Using rifle with shoulder bag may be inconvenient because of opposition between distribution and disposition, i.e. weight distribution and shoulder strap with buttstock disposition. The contradiction is obvious, as operator want to counterpoise bag and rifle, in the same time to place differently buttstock and bag’s shoulder strap.
There is a method to put bag’s strap and bag itself on the same side of a body, just add an attachment pad on the shoulder strap. It consists of two pieces with different parts of fastex on them. Look at the sketch, the bag is simply put on the non-firing side of body, after that strap is crossing the body, every piece of attachment pad (front and rear) is on the another side of body (firing), then fastex is secured and now bag is in place but firing shoulder is clear.
Difference is obvious.
The point is to use shoulder bag and do not interfere with buttstock and sling.
Well, using rifle with shoulder bag is not frequent practice, but if needed, it can be done better.