https://www.airsoftmegastore.com/22263-kwa-30rd-120rd-aeg-cut-off-airsoft-m4-magazine-197-04110-KWA-197-04110&iid=25207
KWA 30rd / 120rd K120C ERG/AEG2.5/AEG3 Mid Capacity Airsoft Magazine | Airsoft Megastore
The KWA Adjustable Cut-Off AEG Magazine lets shooters choose between 30-round or 120-round capacity with just a flick of the switch.