It's not that I dislike the 9mm, I have several but it is what it is. My comment was aimed at the claims by gun writers and others that technology has made the 9mm the equivalent of the .45ACP and .40S&W, so why not the 10mm as well?
I've always took the improvements to the 9mm projectile selections as it has now made the 9mm a good/great option for threats. The 9mm projectiles of past were deep penetrators without reliable expansion or vice versa, new bullet technology (that can be applied to all projectiles) afforded the 9mm to meet criteria that was afforded in the past only to wider meplat projectiles such as the 40 and 45 ACP.
Now maybe the gun writers didn't get that point across or made the wrong interpretation of the projectile makers improvements, but it is not hard to see that the gap between 9mm and the 40/45 has significantly narrowed in performance when it comes to balancing penetration and expansion. That is the real improvement afforded to the 9mm. The 40 already hit the sweet spot on penetration and expansion even with older bullet technology as well as the 45acp. The projectile improvements did improve the 40 and 45acp, but they didn't need as much help in the same area as the 9mm gained, so the gap in performance narrowed.
I like all the service calibers (used to carry daily a 40, which is a great round), but when good controlled expansion bullets came out for the 9mm and the improvements showed up in tests it was clear that the projectile manufacturers achieved a great improvement for the 9mm where the improvement didn't mean as much to the 40 and 45acp as their projectile meplat already afforded some of those characteristics.
So to say it simply the 9mm closed the gap, quite significantly in penetration/expansion performance as compared to 40 and 45acp. So when one is taking consideration magazine capacity, firearm size, recoil, cost of ammunition for training with the improvements to the 9mm projectiles, 9mm starts to look very good as compared to 40 and 45acp as opposed to in the past the 9mm suffered from either due to poor penetration due to rapid expansion, or poor expansion and excessive penetration.
In
Lucky Gunner's ballistic tests:
9mm - Winchester 147gr Ranger T-Series
5-Shot Average Depth = 18.7"
5-Shot Average Expansion = 0.74"
40 S&W - Remington 180gr Ultimate Defense
5-Shot Average Depth = 15.5"
5-Shot Average Expansion = 0.79"
45 ACP - Winchester 230gr Ranger T-Series
5-Shot Average Depth = 14.5"
5-Shot Average Expansion = 1.00"
One can see that the performance is pretty close between all three cartridges. I picked what I thought the best balance of penetration and expansion for each of the respective cartridges. As you can see the 9mm might be a touch on the over-penetration, the 40 S&W load looks like a good balance of penetration and expansion but the expansion is the same as the 9mm. The 45 ACP great expansion, but a little bit shallow on the penetration, would be better if closer to 16" if one needs to shoot through a limb and reach vitals.
So with the projectile improvements other we've been afforded decision based variables such as: cost, recoil, firearm size, and magazine capacity starts to play a greater role in decisions on cartridge when performance has been narrowed.