56TH
Be aware these are very hard on scopes, even airgun rated scopes.
Because they use a sled to make the gun recoilless to the shooter,, the barrel, piston chamber and scope travel forward and back violently during the shot cycle.
That part of the recoil that is normally absorbed by the stock and your shoulder is now absorbed by the scope and mounts.
They are also very heavy.
They are a very well put together air gun usually very accurate, and are excellent shot off the bench.
When I was looking I ended up with a HW97KT, still not sure whether I chose right or not.