10mm is worlds apart of the 9mm europellet (btw the 10mm is actually US made!) The 10mm in fact has more energy at 50 yards than the .45 ACP does at the muzzle and is often used for big game hunting!!!. 10mm is basically the power of the .41 magnum in an auto pistol. 10mm = .400 inches, thus .40 S&W and 10mm bullets are the same ranging from 135gr to 200gr. The 10mm however has a slightly longer case which is much stronger to be able to withstand the magnum spec pressures generated when firing. The .40 S&W case however is NOT simply a shortened 10mm case, as there is significant difference in the case wall thickness, case webbing, primer pocket, etc. The 10mm was a bit too powerful for most people, thus the .40 S&W was designed to achieve the same goal of a 180gr bullet at 950 fps that the 10mm meet and exceeded; albeit with a shorter case due to the 10mm being under loaded to meet those specs.
The 10mm auto is a very fun round to play with, but I wouldn't recommend it for defensive handgun for the following reasons (especially for a first gun):
1) Severe over penetration (liability for hitting bystanders and damaging property, etc)
2) 10mm is sort of a niche cartridge not enjoying the wide spread acceptance of 9mm, .40 S&W and .45 ACP hence ammo isn?t as plentiful.
3) Severe recoil and control issues under rapid fire; think *magnum*
4) Higher ammo cost = buy less ammo = practice less often = makes YOU more dangerous
5) Very few choices of manufactures that make 10mm. Sig and H&K for example, two of the most desirable brands, do not offer a chambering in 10mm at this moment. Colt and S&W 1911 style 10mm frames are no longer in production, leaving you pretty much no other choice for a new 10mm but Glock.
I would suggest 9mm, .40 S&W, or .45 ACP for a defensive sidearm.
.40 S&W is a favorite of mine because it makes the choice for you: you get the mass, momentum, and large bore of the .45 ACP with the velocity, penetration, controllability, and ammo capacity of the 9mm; the best of both words without having to overkill.
I personally carry a fullsize H&K USP .40
H&K is on the expensive side, but then again, so is a Ferrari
😉
I get ammo at $165 a case (1000 rds, or $8.25 box for 180gr FMJ) here in town.
http://members.cox.net/csbaker-az/ammo.jpg