as already said just get a decent top hat and spring guide if your gun has a bar from the middle of the piston that locks into the trigger you will find it a bit of a squeeze the single beast spring that robb does is very pokey and with a decent set of guides will certainly bring your gun upto speed also give all the internals a good polish and decent lube before reassembleyand she should be fine for the next 10 years
S400 Carbine