No way! I just purchased a walther p99 only a few months ago. [beer]

-Case length
-Amount of powder
-Maybe bullet weight
-The barrel has different twist rates.

The slugs used are the same. The 10mm is like a magnum version of the .40, and was actually designed first. You can use heavier bullets with the 10mm and also download it to equal the .40. It will still have a longer overall length. 10mm's really beat up guns too, my friend had a Delta Elite that wasn't very fun to shoot. And it didn't live to long either. Follow the manual and stay within the limits. I wouldn't experiment with bullet weight without exact loading data.

.40 S&W = .40 Short & Weak.  definitely a much downloaded kid sister to  what promised to be an excellent round.  Thank the limp wristed among the boys & girls in blue who can't deal with a little recoil.  If you hand load a .40 with 10mm data, you have just made a hand grenade.

The 10mm is designed for use in a .45 ACP size handgun, typically with a single stack magazine.  The 40 S&W is a shortened, weakened version of the 10mm meant to be used in a 9mm size handgun with a double stack magazine.

At close range, the 10mm does not perform much better than the .45 ACP +P.  Thus there is little merit to it over the .45 except that you can generally get one additional round in the magazine.

You should read Sanow and Marshall's latest book on handgun 'stopping power' before you decide that the .40 is 'short and weak'.  In actual shootings, the lightweight .40 rounds (155 and 135-grain bullets) are doing better than almost all the .45 loads.  The 155-grain Winchester Silvertip at 1205 feet per second has almost 150 more foot-pounds of energy than a 230-grain .45 load, expands to an average diameter of .70, and penetrates an average of 13.5 inches.  With longer barrels like in the Glock 35, .40 loads can closely approach full-power 10mm velocity and energy.

And the .40 was NOT designed for the 'limp-wristed among the boys & girls in blue who can't handle a little recoil'.  It was designed specifically for the FBI by Winchester and Smith and Wesson, when the FBI wanted the 1076 downsized.  Winchester and S&W designed a cartridge that would match the ballistics of the downloaded 10mm round in a 9mm-sized package, which S&W provided in the form of the 4006.  It was the feebs who wanted to download the 10, and I don't consider them to be 'boys and girls in blue', unless you consider cheaps suits as blue uniforms.  I know lots of road cops who carry a full-power 10.  In the right gun, it's an excellent load for duty use- plenty of energy for punching through car windshields, etc.  It does that much better than a .45.  For shooting at unarmored humans, 199 is right- there isn't a whole lot of difference.  For punching through obstacles or shooting at things like black bear or cougars, the full-power 10 has a definite edge.

I load 10mm auto, from my understanding, you can use the same loading dies and bullets for the 40S&W.  The only difference is the amount of powder and overall length.  The full power 10mm is the most powerful round commonly available for service pistols.  It treads pretty closely, but not quite at 41Mag levels in terms of velocity and energy. Check the specs at [url]www.windchester.com[/url]

HELLOOOOOOOOO

PRIMER SIZE!!!!!!!!!!!!!

Aw rats, Weasel beat me to the draw.  Yeah, S&W switched to the small primer when they discovered that the ejector on the mid-size guns hits the edge of a large primer of an unfired round.

At 1205 fps and 155 gr. your foot pounds are right at 500. 10mm rounds can easily be loaded to 650+ ft. lbs. A 200 gr. bullet at 1210 fps for instance.  The 357Sig round is also a good alternative to the .40S&W  I've got all three!!

Yessir,
as much as I love my Dillon 650,
I HATE changing over the
priming system.