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Old 11-16-2019, 04:52 AM
mlg mlg is online now
Join Date: Nov 2004
Posts: 200
HP 40 S&W to 9mm conversion with +P

Can anyone advise of their experience converting a HP 40 S&W to 9mm and using 9mm +P ammo? My question is of durability and longevity. What pound recoil spring are you using? Several smiths recommend against it and if that's the thought why convert? I have one and thinking of using Speer Gold Dot 124+P.

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Old 11-16-2019, 09:16 AM
TNorris TNorris is offline
Join Date: Jan 2018
Location: Chicago
Posts: 485
I wanted to get a .40-9mm conversation barrel years ago but never got around to it. My first HP was in 9mm with the second in .40 cal, at a great price for a new HP. I liked the idea of having two in the same caliber. I then found a new 9mm replacement slide and picked up a EFK 9mm barrel instead. A .22 kit was a no brainer after that... so I could shoot either HP at a lower cost per round, or 9mm in either and .40 in one. I have since picked up another nice .40 and several more in 9mm.

I still don’t understand the need for +P or +P+. I’m pretty happy with standard 124 grain. For me, they seem less pleasant to shoot.

I could be wrong but I think you need to change the ejector on the .40 to effectively shoot 9mm with it. In my memory, the 9mm with the .40 slide worked better than the .40 with the 9mm slide. The .22 works better with the 9mm frame. The only difference, as far as I know, is the ejector. Hehe... or maybe it’s the extractor! It’s been awhile!

Sorry I can’t answer your actual questions. I imagine someone here can.
Have fun with it!
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Old 11-16-2019, 02:18 PM
mlg mlg is online now
Join Date: Nov 2004
Posts: 200
The only thing you need to change is the barrel and recoil springs. I have a recent conversion by Novaks and it works perfect. Thanks for your input.

PS I currently use standard 124 JHP and 115 JHP. The +P has a better track record for LEO's which is why most have gone to it.
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Old 11-17-2019, 06:28 AM
robmkivseries70 robmkivseries70 is offline
Join Date: Sep 2005
Posts: 289
IIRC a 15 pound recoil spring is where to start. Some of that depends upon the weight of the main spring too.
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