WE 3.8 Baby Hi Capa Problem

[Mac4456]

Recently after getting this pistol off of here i took the slide off to see the hop up then as soon as i put i back i loaded a mag and cocked it and the bb's just fall out the barrel and in a 24 round mag only 2 load propely?
Has anybody else experinced this problem if so how do you fix it?
And can you change the whole hop up unit to a TM one?? And where abouts would you purchase one from?