Midway has the Arredondo +5 Base Pad for the Glock 20 / 21 on sale
Save $5.50 thru 21 April
http://www.midwayusa.com/product/511319/arredondo-checkered-extended-magazine-base-pad-5-glock-20-21-nylon-black-and-10-pct-extra-power-spring?cm_vc=ProductFinding
I run them on my MG20 and they work great....no issues on the five I have
(http://i1108.photobucket.com/albums/h414/denstinettm14/MG20-M4_zps0701498d.jpg)