Took my new purchase apart last night to address the rather miserable 4½ ft/lbs of energy it was producing & pulled out a spring shaped like a 'quaver' and a rather messy piston head that was held on with piece of allen key!

My questions are:
1) what kind of pin holds the piston head on - solid / Roll pin or other?
2) Should the piston head buffer be a substantially smaller dia. than the head? - mine is about 3/8" smaller in dia.

Thanks for any help