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Old 04-20-2010, 07:19   #9
Senior Member
Join Date: Mar 2005
Posts: 303
I second the 10-.40 conversion barrel motion. If there's a best case for a conversion barrel, it's between 10mm & .40S&W.

I wouldn't feel too bad using that barrel for carry.

But short of that, .40S&W loadings get surprisingly hot. For instance, with a 180-gr. bullet one max load for .40S&W is 6.7-gr. Unique, which will drive the bullet around 1000 fps according to the Alliant powder reloading manual.

In comparison, I just loaded up some moderate power 10mm rounds last night for self-defense ammo. 180-gr. bullets over 6.6-gr. Unique, which would get me between 1000 and 1050 fps according to the Hornady reloading manual.

Yeah, that's pretty much the same load.

But... the difference is using that in a .40S&W is a super hot max load, which will be pusing the limits of the gun, brass, recoil spring, and shooter's hand. Accuracy will suffer. In a 10mm, I know that load is extremely accurate and shoots fairly soft out of the G20.

That's the real beauty of 10mm IMO. You get nice hot loads right in the sweet spot of usability. Yeah, you can go nuclear also but then you may not hit what you're aiming for. So sure, go for it - use the .40S&W loads and see what happens. There's a lot of overlap between the two, and a hot .40S&W may make a very nice shooting, 50-60%+ 10mm load.
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