Re: 541-T mag
the model 77 5 round mags are almost identical but work much much better. I think the plastic, ugh, is ever so slightly thicker.
the 10 round model 77 are no better than the original 541 10 round mags. they don't work. the metal spring clip in the back doesn't have enough tension to hold the rounds in the mag at full. I have taken the springs off and squeezed them but it had no effect.
The model 522 mags fit in the chamber but won't feed. (i have made this mistake also) Its too bad there so hard to get because they would probably be the best. You have to file down the plastic piece in between the mag spring and the round to get the correct angle and remove the round button-esk thing on the side. (not easy to do by eyeing it up)
good luck, if you find some better mags let us all know please
dgwelsh