Thanks all, all info gleaned has helped a lot, howvere LOL..
SSG I am still on the fence, reason is that the cocking/firing sequence
1 The "sealed" unit can only extened so far untill hammer is free flight hence the short spring. similar to a SSG
2 Hammer then carries on for 2..5mm as the valve stem is hit by the now free flight hammer. Same as a SSG
3 Stem is now free to return with out fighting the hammer "debounced" in effect, same as SSG
There is a tiny amount of pressure left on the stem, but WAY less than if not a restricted spring/hammer unit.
Different to other guns I have as factory, so what are the thoughts?
a halfway house? with a fraction shorter stem it will work as an SSG debouce?
I aquired 3 13XX at once (swaps

) amazing how the transfer ports vary on Crosmans