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UMP 45 to 40 cal. swap?

DevilDog03

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Ok I’ve looked at my bolt and tried finding definite answers so here’s my question.

I have a TBT HK USC to UMP 45 acp conversion from Tommy and I just bought a 40 cal bolt barrel spring and mags.

So will the parts kit bolt 40 cal drop into my UMP or will I have to send the bolt off to be milled down? Will the bolt I’m getting not look like this?


I am getting swap parts tomorrow so kinda curious today about tomorrow. I really hope my receiver is already been fixed to accept the 40 cal bolt?

Thanks

Pic of my current 45 bolt.
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ORL-LLC

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Good question, not that I want to convert my UMP45 down to .40 as I have no other .40 weapons,
but 10mm might be interesting. . . .
 

DevilDog03

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Well I have 1K 40 cal ammo so I bought the parts to shoot both calibers. PITA I know Tommy is probably busy doing T36 rec. work to mill a bolt probably at the moment.
 

Mitchell

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Those bolts are REALLY hard. I would recommend a surface grinder or even a bench top belt grinder. I have done a few of these and abandoned the mill altogether. I built a jig to hold the bolt square and ran the belt all the way to the edge of table and let loose. Took about 5 minutes with minimal pressure. Keep your calipers near by, you certainly don’t want it rattling around in the receiver!
 

Mitchell

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Sorry, didn’t read that correctly. Unlikely it will fall right in. Will likely need to be machined down.
 

DevilDog03

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Ok I got the 40 cal bolt today and no joy it has to go under the mill in order to slide into receiver so for all who does not know if changing calibers from 45 ACP to a 40 Cal bolt on a USC to UMP conversion it will have to be worked on.

3513A0CD-BA6D-49D4-8CA0-C086955AF2DD.jpeg
227B691D-265A-4639-88A2-0CDE8C73258E.jpeg
 

DevilDog03

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Those bolts are REALLY hard. I would recommend a surface grinder or even a bench top belt grinder. I have done a few of these and abandoned the mill altogether. I built a jig to hold the bolt square and ran the belt all the way to the edge of table and let loose. Took about 5 minutes with minimal pressure. Keep your calipers near by, you certainly don’t want it rattling around in the receiver!
I would try myself but IDK I would end up doing too much and yes a 400$ bolt rattling around.
You can’t put it back right.
 

AGG

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I would try myself but IDK I would end up doing too much and yes a 400$ bolt rattling around.
You can’t put it back right.

I would not muck it up--- those bolts are difficult to find in that caliber. ;)

Tony
 

DevilDog03

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I would not muck it up--- those bolts are difficult to find in that caliber. ;)

Tony
Yes I have reached out to Tommy with a work order and while I’m at it I might send rec. to get ejection port opened up?
 

DevilDog03

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Ok at this point no reply from TBT through work orders as impatient as I am so sent it more local for milling to B ops Defense I have used them before and they are pretty reliable so it’s on its way to PA. They do conversions from USCs to UMPs so talked to Wes for those of you who are familiar with them and he accepted the work.
Should be a pretty quick affair I’ll post pics of the work when I get it back. Kinda pumped up like to see the difference in how the 40 cal shoots VS 45 ACP In the UMP.
 

Omega21

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Hi @DevilDog03 Have you gotten the bolt back? I wanted to offer some info to the folks looking at this. The reason the bolt needed milling is NOT because of transitioning from 45 to 40. It's because you are using a full auto bolt designed for a UMP not a USC receiver. The same thing has to be done when inserting a UMP45 bolt into a USC conversion or USC to UMP fuse job. HK does this specifically so you can't "convert" your USC to full auto by swapping out the bolt (among other things) so they narrowed the dimensions of the USC receiver. Easy fix. I'd be curious to hear how much B Ops Defense charged you. AviatorDave does this work for $99 and TB does it for $65 if I recall correctly. They also re-blue the milled part. IF you get a 9mm bolt, you will need to do the same thing.
Also,
In your original post, you mentioned getting a new bolt, barrel, mag and spring. What spring are you referring to?
 

DevilDog03

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I did the get the bolt back and test fired the gun everything worked no bolt rattle it was 110$ shipped from B Ops defense and the turnaround was 2 weeks.
Been real busy I will put up some pics of their work on the bolt.
TB never replied I’m sure due to the T36 work he’s been doing and Dave I had saw where he had done this work but tried Wes at Bops.
 
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AGG

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I did the get the bolt back and test fired the gun everything worked no bolt rattle it was 110$ shipped from B Ops defense and the turnaround was 2 weeks.
Been real busy I will put up some pics of their work on the bolt.
TB never replied I’m sure due to the T36 work he’s been doing and Dave I had saw where he had done this work but tried Wes at Bops.

Thanks for the update. ;)

Tony
 

DevilDog03

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Alright here’s the pics of semi auto bolt 40 S and W and the registered HK TBT converted SBR It used in. Like stated everything’s A OK no movement and is still slightly stubborn to slide into the receiver by itself.

For anyone’s info it cane be done for a small cost on the builders end but as we all know caliber kits are not cheap but cool to have both 40 and 45.

Now I just need to save and buy the 9MM kit lol.

Thanks
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AGG

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Alright here’s the pics of semi auto bolt 40 S and W and the registered HK TBT converted SBR It used in. Like stated everything’s A OK no movement and is still slightly stubborn to slide into the receiver by itself.

For anyone’s info it cane be done for a small cost on the builders end but as we all know caliber kits are not cheap but cool to have both 40 and 45.

Now I just need to save and buy the 9MM kit lol.

Thanks

Thanks for the update and pictorial--- nice CQB. ;)

Tony
 
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