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Discussion Starter #1
Couple of interesting pics. I was able to stick about 20 10mm in a UMP 45 mag. What's the chances of reaming a .40 chamber and modifying a .40 mag to hold 10mm??? Interesting little thought, ain't it? Here's the pics I have.



 

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What's the chances of reaming a .40 chamber and modifying a .40 mag to hold 10mm??? Interesting little thought, ain't it? Here's the pics I have.
Just about anything is possible, its just a question of how bad you want it, and if you've got the cash to back the want.
 

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Discussion Starter #3
I don't really see a lot of cost involved. Just have to find someone to ream a barrel. Someone here was trying their hand at modding a 40 mag to work with 45.
 

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The 40 mag mod was a success for the 45 so it should work.

W/e floats your boat.
 

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Discussion Starter #5
There you are. I was following that thread but never saw where you succeeded in converting it. I may try it when I finally pick up another USC.
 

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Big Chris 304 did some USP conversions (.40 to 10mm). You might want to talk to him before you do anything.
 

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Wasn't me, I believe the last thing he said was it took him a couple of hours to get tweaked just right with a long file his relative made for him (which I'll take to be success).

It's in the "ump mags wtf" thread (or something like that).

Regardless it would be nice to see a more unique USC/UMP setup.
 

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Discussion Starter #9
I suspect you'll have a bit of experimenting to get the right spring rates to get it run reliably.
I'm sure that is going to be the toughest part of this. Are the .40 barrels fluted?
 

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The .40 UMP barrels ARE fluted. You're going to have to take my word for it, I've been working on a friend's car on and off most of the day and getting up and digging out the barrel is about all I'm up for right now! The spring is captured, you're going to have to design a system to get around that. I think Chopstix Kid was thinking about this and he has machining capabilities so he might be the person to talk to about that. If not I'm sure I could get it done (machining etc).
 

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Discussion Starter #11
Copy that lohe. Wonder if anyone made a non-fluted 40 barrel. Maybe one of the old top notch barrels?
 

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Copy that lohe. Wonder if anyone made a non-fluted 40 barrel. Maybe one of the old top notch barrels?
Finding any non HK .40 barrel is going to be a pain. Call Adam at HKparts, he gets TN barrels in occasionally. I don't know if they are fluted though. The case length difference is something like 3.6mm.. I don't think that it being not fluted for that short of a length will make a huge difference. Fluting is really important with a roller lock gun (from what I've read) but not so much with a non roller lock. Looking at the 9mm conversion kits one of the barrels is fluted and the other is not and they both run really well from everything I've heard.
 

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To me the biggest issue is spring and buffer mass. My limited understanding of the UMP is, that the UMP is strictly blow back. I'd think that low power 10mm would run just fine using a standard .40 S&W bolt. The problem is that there is such a wide range of power in 10mm AUTO.

I have some experience with the Colt 9mm M16 system. Using a 9mm upper, Colt designed the 9mm buffer to be extra heavy compared to the standard carbine buffer to have the proper delay in the bolt "opening" during the high pressure phase of the cycle. I notched that a guy with a M16 9mm set up that seemed as though the gun was running very fast. I asked him about his set up. He was using a standard "H" buffer. We got to looking at his brass on the ground. All of it was bulged. Looking inside the upper, there was some brass shards inside the upper. He had said that he noticed a round sounded different and he stopped. He said he checked the barrel but didn't see a blockage, so he thought it might have been an underpowered round.

There were brass shards inside the upper. With that and the brass being bulged, I told him I though a case had ruptured. In a blow back gun, the mass of the bolt/buffer is what holds the bolt "closed" during the high pressure phase. If the mass is too small the bolt will "open" too soon. Lucky for him, it ruptured away from the ejection port instead of toward the ejection port. Had it ruptured toward the ejection port, he might have gotten brass shards in his face.

Do I know that for a fact? No, but if I'm right, getting brass shards in the face from a ruptured casing would not be good. So my concern for a 10mm AUTO UMP would be that a standard .40 S&W bolt would not have enough mass to hold the bolt "closed" during the high pressure phase when using full power 10mm AUTO rounds. With the extra power of full power rounds, there could be a catastrophic failure. I certainly wouldn't want to be the one holding the 10mm UMP conversion, if there was a catastrophic failure. YMMV.

Scott
 

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The 10mm UMP has been done. One member on this board did it using modified M3 mags and a Grease Gun lower. He did it as an SBR, and from the sound of it it was quite effective. I too am interested in this conversion, but the extra pressure from a 16 inch barrel does concern me.
 

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You have the pressure from the bullet trying to push the bolt back from the front of the bolt and the spring trying to push the bolt forward from the back and the tendency of the mass of the bolt being ‘at rest’ to want to stay at rest. So, if you increase the spring rate of the spring or even take a small length of another spring and add it to the captivated section of the spring assembly you should be able to counter the greater pressure of the 10mm (of course the spring would have to be fully 'captivated'). You might take a UMP spring and cut it into varied lengths and try them out to see how the rifle fires. I would build some sort of rig to hold the UMP to a table and pull the trigger with a string, personally ;)
 

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Why are the 45 hk ump barrels so hard to find? seems like all other cals are so much easier. But a 10mm sounds like fun!
 

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Why are the 45 hk ump barrels so hard to find? seems like all other cals are so much easier. But a 10mm sounds like fun!
Where are you finding actual HK UMP 9mm and .40 barrels? The only barrels that I know of that are 'easy to find' are the 9mm barrels being made by Glenn and Mike or the .45 barrel by HDPS.
 

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Necro thread resurrection... Because this is what I'm doing to my UMP.

Base platform: UMP converted USC with my ACR stock conversion block, Navy conversion kit with UMP lower with complete trigger/hammer/sear swap, milled the upper here at my house, had Tommy Bostic do the bolt milling on a factory UMP .40 bolt, SBR'd and suppressed.

I bought a second .40 barrel off Gunbroker to keep in reserve because my USC/UMP is SBR'd and BATF says I can change calibers but I must ALWAYS have the ability to switch back to the original filed caliber. My original .40 barrel I had threaded 9/16x24 in front for a suppressor which has worked quite well also. I'm running the original .40 UMP BCG (with the heavier tungsten insert still in it) and it fires just fine once we reamed the chamber for the longer 10mm round.

One thing I found is that yes, the chamber is fluted, but we're only adding .30" of unfluted chamber deeper into the barrel and right where it meets the shoulder, so it shouldn't be and was not a problem. Extraction functions fine, bolt locks back on an empty mag just fine, that's not the issue at all. Recoil feels about the same as it was with .40, but granted that's with 10mm 185gr JHP from Freedom Munitions, not the REAL 10mm loads from Buffalo Bore or Underwood (loaded a lot hotter).

Originally the idea was that I'd also be able to shoot .40 in it still because I can in my Glock 29, but the issue is in how the round is held in the Glock - it'll work in a Glock but with the way the UMP bolt works, the .40 bullet has nothing to keep it from dropping all the way to the chamber shoulder so that will not work in a UMP.

The issue I'm running into is mags. The UMP .40 mag isn't anywhere near deep enough for the longer 10mm round. I bought several .45 mags but the problem with THOSE is that the upper retention / feed lips are a LOT wider for the wider .45 casing, and they won't retain the 10mm round, it just pops out the top. I tried just one round carefully placed in the mag and it fed OK, won't know about mag spring pressure until I get the feed ramps right.

In comparing mags (I can't find the other referenced thread UMP Mags wtf) it appears there is a plastic blocking tab that runs down the length of the magazine in the .40 caliber that keep the bullet from seating as deeply back. If that were removed, the 10mm round would fit. I may try that first, as the alternative is taking a Bondic pen and adding plastic to the lips of the .45 mags then filing them straight.

Just bookmarking brainstorming ideas and seeing if anyone else has actually done it with ALL parts from UMP's (not grease gun lowers). I'd like to keep the ability to also run .45 still in those mags just to have every caliber still covered (I have a 9mm kit as well), so I'll have to be careful with adding material (although I can always just file it back down).
 
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