I am sure this topic has been covered many times before. I've read so many reports by police agencies , by the FBI and so called armchair experts. That the usual gun fight is settled within five feet and the average is three shots fired in 6 seconds.
Am I being over the top paranoid by carrying an extra reload on me? I carry a 9mm with a 15rd mag, and I carry a spare of the same round count. I don't go to any bad areas, am very aware of my surroundings. I just want the extra for that just in case 100,000 to 1 time if needed. Does anyone else plan this way when carrying ccw?
If you feel comfort carrying the extra magazine, it's your call.
There's been some variations repeated in the 'average gun fight statistics' numbers bandied about over the years. We used to tell people that most shootings occurred in conditions of diminished light, within 0-6 feet, and were over within 2-3 seconds.
Spare ammunition is ... spare ammunition. I used to carry 2 speedloaders in the older service revolver days, although there were times when I worked beats a little further out (for hope of getting cover) when I carried an extra 1-2 speedloaders or speedstrips. Nowadays, I carry an extra 5rd speedstrip when I carry one of my 5-shot snubs. It doesn't take up much room alongside my pocket-holster, so why not? There have been times, when I thought the risk assessment might be higher, when I'd drop 2-3 speedloaders/strips in a jacket pocket.
When I carry one of my 9, .40 or .45 pistols, I typically carry a spare magazine (regardless of capacity, or whether they're single or double stack). Old habit. In my plainclothes days I carried either 1 or 2 spare magazines (policy was at least a single spare was to be carried in plainclothes assignments).
Now, practically speaking, having a spare magazine at hand is useful for resolving magazine-related problems. As a longtime trainer of LE, and several years working with CCW licensees, I've see all manner of shooter-induced problems occur during training and quals that required a fresh magazine. People can fumble under even moderate 'range stress', and do things they never thought they'd do, like depress a magazine catch and dump a full magazine when they're shooting, or just manipulating their pistol. Baffles the hell out of most people when they do something they didn't think they were doing.
Then, there's actual
magazine problems.
Like not realizing one-too-many bumps against a veh door frame, or a seat belt buckle, caused a buttplate to become damaged and dump loose rounds out the bottom of the magazine. Or, have the magazine catch button depressed enough to dislodge the magazine, causing it to drop just enough to be out-of-position for feeding, or fall entirely free of the grip frame. Coming back to your veh and seeing your primary magazine sitting on the seat, or on the floor next to the seat, or even on the ground outside the veh door, can be ... disconcerting, to say the least.
Then, there's the chance for a kinked magazine spring, or tipped follower, to cause a feeding problem when the magazine load doesn't rise in the magazine after a shot or two. In older days one of the gun companies used to caution armorers that the normal bump/contact between rounds in a double stack magazine, resulting from normal walking, might over time cause some mild deformation of brass cases (think flat spots), which might interfere with normal movement of the rounds during live fire. Never saw that myself, but gun companies don't come up with stuff like that on their own, meaning they've usually heard it from agency users at one time or another, and passed it on during armorer classes.
Sometimes a particularly nasty type of feeding stoppage (stubborn double feed) might require dumping/ripping the primary mag to resolve it, which means a fresh mag would be needed.
Seeing someone unintentionally ... dump their primary mag during some frenetic shooting drill ... and see the mag find that dark shadow at their feet ... or the deep puddle of rain water ... or bounce a step or two away (or into the bush next to where they're standing in the real world) ... is usually best resolved by having another magazine available.
So, situational context and risk mitigation might make having a spare pistol magazine handy, but not only for the 'extra' ammunition after running a primary magazine dry.
Suit yourself.
If you ever actually need it, at some point it'll likely become part of the chain of evidence gathered during the shooting investigation, anyway.