Its supposed to be tough with the bolt closed, especially with a loaded mag. essentially you are forcing the compressed spring about another 1/8th to 1/4 inch down before the mag locks into place. I always lock the bolt open, insert mag and drop the bolt with the release because sometimes i will put a loaded mag in and charge the rifle to have the mag fall out because it didnt lock into place and i thought it did... I use magpul p-mag 20 rd mags. they are the best in the west IMO
