Having bought this old Stevens 94 that originally had no furniture which I've added recently. I had to decide on how to carry extra ammo if I needed it, so I decided on a shoulder strap with a 15 round holder and I already had the stock sleave that had to be form-fitted to the stock manually. However, I soon realized my personal do's and don'ts on this idea so here's what I've come up with as personal tactical care of this fine arm.
In order to avoid the heavy weighted strap from bouncing with the high recoil, I found that holding the strap with the fore stock will keep your left-hand happy vs letting the sling bounce around openly, striking your hand or even damaging the gun in the process.
Your stock sleave is a good support shell holder for cleaning rounds, or forbid shells you hope you never have to use, like emergency flares.
The orientation of the shells on the strap should be augmented for the quickest hand that can reach them. Up front the cases should be oriented to your left hand while the back shells should be retrieved from the right hand.