I have the Plus model, 15 rd. double stack and it was stiff. It got better after shooting a few clips. I do spray some Rem. dry lube in my mags on all my semi-autos. A clip loader would help press down a round in the clip while you insert another round. The Bersa website has them for sale. I have to use one that came with my Taurus .45 due to stiff springs in the mag.
ST6 - Adco Super Thumb Loader - For Bersa 380