Crossman blaze rear open sight problem ?

Hi guys, recently bough acrossman blaze .177 NP .

Started 40 feet half inch circke target, Inmediatly noted that pellets were hitting low, started the process of rising rear open sigth but best result was picture 1, tryed to go al little bit up to reach the circke wth hist but spring and elevation regulation screw jumped off along with the srping. Tha meant that I couldnt go up from that position.
The problem was "solved" by adding some washers to rise the whole rear sight., result was picture two, good grouping of hits an almos all right on target ( hal inch target)
Im quite surprised I had to do that fix since the gun is just perfect other than that. 
Any Ideas on what can be wrong, Everithing looks normal , end sight corresponds to model and rear one too. ( started to think that may be too high end sight from wron model but they dont),
Cant get what is wrong, any ideas will be more than wellcome
Regards from south america friends!
I was unable to upload my images but Im pretty sure folks can figure about situation dont you?

Alfredo