isnt 10mm closer to 40 than it is 45? 10mm a longer .40 with more powder, but its nothing like a .45 picking between 45 and 10mm is the same as picking between 45 and 40....if you want a lighter bullet with more energy but a smaller wound channel, 10mm is what you want (or 40 if thats the only option)....if you want a slower heavier bullet then you want a 45 personally, i like .40, .357sig, and 10mm all better than i like 45....i would rank it 10mm, .357sig, .40, and then 45 in order of what caliber ide choose for SD in all reality, any of the 4 are going to put somebody out of commission......so buy whichever caliber you feel better shooting....some people hate how 10mm shoots and prefer 45, but some people dont mind it in my opinion, 10mm is the ultimate SD caliber....i had to settle for .40 because HK doesnt make a 10mm...but if i bought a glock, thats the caliber i would choose....ide like to own a glock 29 in 10mm as a BUG 10mm is expensive to shoot....might not be a good beginners gun because you will want a lot of practice and a lot of trigger time, which gets expensive...but if youve been shooting awhile and just want another gun the 10mm should be great for you