The BAM XS-B26 is a Chinese copy of the Beeman R9. It is available in 2 calibres: .177, and .22. It is a break barrel type air rifle.
The 26 in B26 is for 26mm chamber, but it never went in to production at 26mm.
It is a 25mm chamber. The Beeman R9 has 26mm, where the B26 does NOT not have the 26mm chamber.