The rifle referred to was originally the B20, imported by SMK and given their designation XS20, it had a 25mm piston.
Around 2005/6 the piston diameter was increased to 26 mm and had the international designation B26, but SMK still called it the XS20
There was a version with a thumbhole stock, but a very high comb (too high) being the B26-2.
However the B26-2 was never imported into the UK in any great numbers.
They did copy the Rekord trigger but cut corners with the top of thetrigger blade i.e.shaped lobes of metal instead of impressed rollers.
A good fix was to buy a HW trigger blade then drill its axis hole to 3mm to accomodate the fatter axis pin on the B26.
In that way, you got the proper 2 stage triggerand a lighter smoother pull.
Subsequent versions did away with the Rekord copy trigger altogether but still kept the SMK designation of XS20
My .22 is now17 years old and notwithstanding being made of "monkey metal", can still shoot the nads off a gnat out to 45yds