However on the range having fought through the plastic to get a mag to use up life ex ammo, one lets rip down range to find I only fired off 18 rounds out of 20... Asking an Armourer what gives, he points out that they would often get bored filling them, so it was anyone's guess how many rounds were in the mags
When I was a pongo, we only used to put 18 rounds in our SLR mags. This is because number 19 and 20 compress the mag spring so much, it loses a lot of it's springiness and the chances of having a jam in the first two shots were greatly increased.