I recently purchased my first firearm - a Glock 21sf. I have 3 mags for it. Last night was my first attempt to put some target rounds (Remington 45acp 230g) into 2 cartridges. It got harder and harder as I put them in. I was only able to get 10 into each of them and they're supposed to hold 13 max. Am I doing something wrong or is this typical? Thanks.