I kept my loaded 9mm mag in the pistol; I had a leather holster so it was safe enough. I was slim hipped enough to wear it on a waist belt whilst sitting in the armoured seat - others couldn't!. Same with the SA-80. Can't recall where I kept the second mag for that one but it was at immediate readiness.
I remember "Sid" B****er panicking having dropped and lost a round outside the armoury, only to be hugely relieved when he found it lurking in the fabric surround of his flying suit knee-pad.