WE Hi Cappa 4.3 mags
 

I'm looking to pick up an extra mag or two for my WE hi capa 4.3. Are the 5.1 magazines compatible with the 4.3 frame?

Yep, 4.3 mags are only shorter than the 5.1 at the bottom. Mag catch cut is at the same location and the bumper starts at the same point, just ends a little earlier on the 4.3.

would it work the other way i have a hi-cappa 5.1 but all i can find is 4.3 mags

Works both ways.

LOL dude, you just contradicted your earlier sentence, it doesn't work the other way around, because the 4.3 uses shorter mags than the 5.1, the top of the mag wont ever reach the slide chamber.

Please reread what I wrote earlier. Both 5.1 and 4.3 bumper starts at the same distance from the top of the mag. In other words, both 5.1 and 4.3 Hi-Capas have the same grip length. The only difference between the sizes of the two mags are what sticks out.