Arcturus AR MOD1 M4 variable capacity mag

so... while online hunting for variable capacity mags, i came across this Arcturus AR MOD1 M4/M16 30/130rd Variable-Cap Windowed EMM Magazine. what a mouthful... but they were the only mags with the 30/130 variable option that i could snag in the same day. so i jumped on that shit real quick. so heres the "guide" to switch it from 130 round capacity, to 30 round capacity. hope this helps the next guy or gal when purchasing these bad boys. also... forgive my terrible editing and lack of knowledge. IM STILL LEARNING OKAAAAAAAY! link: https://blackblitzairsoft.com/products/arcturus-ar-mod1-m4-m16-30-130rd-variable-cap-windowed-emm-magazine-black-single-pack-of-5