To antagonize your expectations
:
I've installed one for my client on a G&P before(I believe this was Drache's G&P SAMR a year or two ago).
It worked great, trigger master full auto no problem with hicap that it came with.
You maybe correct to assume that the nozzle that reaches into the mag is not long enough. Try epoxying a bit of material onto the retainer lip end of the nozzle.