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Discussion Starter · #1 ·
I am hoping one of the gurus here (thinking maybe you Dane, as you have done this with Kimbers I think) can help me with a project. I have a 40S&W gun that I have rechambered to 10mm. I is working well and is very accurate, I have just one issue. When I inspect the fired brass there is a slight ring near the end of the brass. From what I can tell the chamber of the gun (HK) might be a looser chamber than the reamer makes (clymer). In other words the extension of the chamber (the part that I reamed) is slightly undersized as compared to the original portion. When the round fires the brass expands more in the .40S&W portion of the chamber than the new, longer 10mm portion. How can I make it all match in dimension?
 

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Discussion Starter · #3 ·
A USP40F rechambered to 10mm. Para P-16 mags instaed of USP mags. Have to keep 10mm loaded to no more than 1.250" to feed properly. Open ejection port to allow loaded 10mm round to eject. Swap magazine catch to USP45F.

I haven't done the mags yet, but I have everything else done. A guy named Monte told me how to do it. He did several up in Alaska.

I have shot it (single loading) and it does quite well. I started with 180g bullets at 40S&W power levels and went up to 11.5g of Blue Dot (.5 over max for 10mm per Speer No. 13) and no problems. No signs of excess pressure either. At first I was disappointed with accuracy at the lower levels (10.0g Blue Dot I think), but as the power level increased accuracy improved greatly.

Looks like a keeper
 

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I have heard of this being done. If you wouldn't mine, could you email me some more info on it at your convenience?

My email's in my profile.

Cheers!

J
 

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"How can I make it all match in dimension?"
Things like what you have just done, scare me...VOODOO guns :eek:


There is a reason that the HK USP 45 is larger physically. The 10 mm works at higher CUP pressures than the 45 by a LONG ways. Keeper? Not in my safe, thank you.

So how do you fix it? New barrel (I might suggest BarSto) or an over size reamer will take out the "collar". The over size reamer will make things even less safe IMO. Good luck :roll:

<font size=-1>[ This Message was edited by: Dane Burns on 2001-11-19 21:16 ]</font>
 

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Discussion Starter · #6 ·
Well I can understand that conversions like my voodoo gun can and do scare professional gunsmiths. I understand the risk involved with it and as such assume my own risk. While I do not claim to be anything near a gunsmith I did research into it a fair amount before diving in. I have spoken to a gunsmith in Alaska that has done this for his own carry piece as well as for half a dozen or so others. He proof tested it with 200 grainers at 1400fps and settled on a carry load of 1300 fps with the 200s. He has to date fired over 5,000 rounds through it without failure. Does this mean it's okay? Maybe not, but 10mm is to me what 9x23 is to many on this board.

My thought process here is simple, which could be my problem :smile: The USP40 was designed as a .40S&W gun, unlike many others that were 9mm built over as a .40S&W. This fact alone means to me that it is stronger than other .40 S&W platforms. As far as the, "10mm is higher pressure than .45 and the fact that the USP45 is a larger platform." I don't know that that matters as much as people may think (this is a common argument for those that think the 10mm USP is a bad idea). After all, the 9x23 is higher pressure than the .45ACP but 1911s are converted all of the time. In addition, the USP357C is a smaller yet version of the USP and it is chambered for the .357 Sig which operates at 40,000psi max pressure.

We have the USP40 which handles the .40 S&W cartridge at max 35,000psi. The USP357C which handles the .357 Sig at a max of 40,000psi in a smaller package. And the USP45F & USP45C which are larger than their .40 S&W and .357 Sig counterparts handling the lower pressure .45 ACP at max 21,000psi. The 10mm with a max operating pressure between the .40 & .357 at 37,500psi. My logic is that the USP45F & C are larger because the .45ACP cartridge is larger.

Now although the 10mm is lower pressure than the 357 Sig, recoil for me is greater with the 10mm duw to heavier bullets. A 200g JHP @ 1200 recoils more than a 125g JHP @ 1400 in my hands. I don't know if there is a mathematical equation to show the relationship of fpe to recoil but I would assume that 10mm would be harder on a gun than 357Sig despite it's lower pressure. I could be wrong and please correct me if I am.

On a slightly less correlated note: Glock has the G20 and G29, both in 10mm. The G29 is smaller than the USP40F yet can still handle the more potent 10mm. I also think that polymer framed guns will be more forgiving than a steel or aluminum frame.

All in all I guess I'm saying I don't think pressure matters as much as energy. Which in this case means I'm saying that based on pressure as I understand it, it is not the sole reason for a gun design or it's ability to handle a cartridge. On the other hand, I am saying that 10mm develops more energy or recoil energy which in my interpretation means more stress to the gun. So in short, I don't think this is a bad idea based on pressure alone, but it may be a bad idea regardless of pressure. Factor in the anecdotal evidence from the gunsmith in Alaska that has not had any problems, my love for the 10mm, and my (maybe poor) judgement and I chose and do choose to do it regardless.

I specifically asked you for your input Dane, and I am very appreciative for it. As I said I am not a gunsmith and do not even play one on TV, so if any of my assumptions or information is wrong, or you find fault with it, I would be more than willing to hear it. I have been surfing assorted gun boards for a few years now and of all the posters I find you to be among the top of the list when it comes to sound knowledge and advice. I would commision you to build me a 9x23 1911 but I have instead commisioned my wife to have our fourth child, so unfortunately for me it's not in the finances for some time. Of course another child is a whole 'nother kind of joy.

I guess I just want to say that my argument is based on my logic which may not be right, and I would be more than willing to hear your thoughts and/or rebuttal of my information. Have you ever run into the collar issue on your Kimber conversions? Or do you just avoid it by replacing the barrel with a new 10mm one? Thanks again for your input.
 

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In my youth I did things like solo 5.11. I rememebr when challenged on my sanity commenting it was like "walking down a side walk for me".

I have also worked with lots of wild cats, things like 9mm @ major (you don't want to know the CUP that one works at) 38 super at major and the wonderkin 9x23 with a 147 doing 1400fps. I have had lots of voodoo guns. I would NEVER use one for carry. Too many reasons to list on that one, safety, liability, reliability among the most serious.

I like "safe and sane" now. Doesn't mean what you did isn't and it always takes innovative thinkers to come up with new ideas.

One way to make it safer is add a BarSto.
 

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Discussion Starter · #8 ·
Dane, do you ever ream the Kimber's to 10mm or do you just put in a Barsto?

Before I posted this question I actually contacted Barsto about a barrel, no reply yet. Does anyone have a phone number for them?

I like the idea of a Barsto anyway, just because I can fit it to the gun and get better accuracy anyway. But I would like to fix this barrel just for the sense of accomplishment. Here are a few questions: Did I do something wrong to cause the collar?

Is my assumption right that the HK chamber is a little looser than the reamer's dimensions?

Is there a brand of reamer that would be .001 looser?

Is there a way to use my Clymer reamer to correct it? Or polish it with a different tool to make it uniform?

I used a Clymer finishing reamer, used tapping/cutting oil and slowly cut the chamber deeper using a tap handle. That's about it. As always, thanks in advance.
 

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As to the pressure issues, many folks get confused as to what matters.
AN OVERSIMPLFIED ANSWER!(I'm not the sharpest pencil in the drawer)
It ain't just the pressure! Breech thrust is the big issue as to what the locking mechanism can support. Breech thrust is the force applied to the breech face/locking surfaces in a direction opposite the bullet. The operating pressure multiplied by the surface area of the breech is the breech thrust. That is why you see guns like the TC Contender chambered for 45-70 but not 308. The available locking surface is not large enough to resist the force applied over time. The failure may be immediate & violent or simply wear over (a relatively short) time to the point that the gun becomes too loose to function properly/safely.
Certainly there are others who are smarter than me who can explain this better or present more factual data, but that is it in a nutshell. Not saying that what you did is unsafe, but someone needs to do the math on it to get a handle on what is really happening.
 

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"Certainly there are others who are smarter than me who can explain this better or present more factual data, but that is it in a nutshell. Not saying that what you did is unsafe, but someone needs to do the math on it to get a handle on what is really happening.
Thank you sir :grin: You said it better than I. I have neither the inclination or the time to follow through on another wild cat.

But I know that HK had both, when they designed the USP. For some odd reason they didn't chamber the 9mm/40 platform in 10mm but they did chamber the locked breech MP-5 in 10 and 40.

The large frame USP had proto types done in 45 and 10mm. I got figure those German engineers actually have a clue...hell, I am just a has been climber doing gun plumbing :grin:
 
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