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I'm been toying with the idea of switching over my TBostic built UMP45 to a 9mm version. I thought it would be nice to shoot the UMP more without slinging a ton of 45 down range. I already have a DJ Getz MP5 clone which runs like a top. For those who have both calibers, Is it worth switching over from the 45 to the 9? Interested to hear some thoughts on the idea.
 

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My understanding is the USC ejection port causes issues with 40 & 9. Ymmv.

I just got some 9mm parts, because....why not. But I intend to use in a TMP receiver.
 

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Do yourself a favor and keep it as a .45. I tried it using the HK Parts kit. Had Tom Bostic do the conversion. It chewed up brass and had ejection issues. I even sent it to the individual who made the conversion parts and got the line “nothing wrong here”.

Point is, stick with real genuine HK parts as much as possible. Unless you come across a real UMP 9 parts kit (last I saw was over $2500-3500 with a short barrel), it is not worth the headache. Consider the fact you can buy an APC 9 Pro or SP5, both of those options are better 9 mm SMGs than the UMP 9 in my opinion. This comes from someone who owns a UMP 45 and loves it (it is my favorite PCC by far, I get a grin every time I shoot it). The APC 9 Pro is superior to the UMP 9. I have mind set up for home defense/PCC matches. Food for thought.
 

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When SP5s and good clones exist, there’s really no reason to shoot 9mm through a different platform. KISS.
 

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I'm been toying with the idea of switching over my TBostic built UMP45 to a 9mm version. I thought it would be nice to shoot the UMP more without slinging a ton of 45 down range. I already have a DJ Getz MP5 clone which runs like a top. For those who have both calibers, Is it worth switching over from the 45 to the 9? Interested to hear some thoughts on the idea.
I have both.

Lighter, easier to shoot, cheaper to shoot, suppresses well. Not an MP5, but still a different gun to have.
 

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I’d definitely keep it 45.

Plenty of 9mm options available, not so many 45ACP.
 

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The UMP platform is excellent in 9mm! I've been shooting 9mm kits in USC 45s for years. No problems. Just don't use weak 9mm ammo.


Air gun Trigger Gun barrel Machine gun Gun accessory
 

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HK Shooting Team
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oh, if you want a big clunky blow back 9mm (big bolt slamming backwards)....go try a CZ Scorpion before you convert to a 9mm UMP and you will quickly realize why 9mm sucks in the UMP!!!!!
 

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I must admit... I see 9mm as more of a novelty round for the UMP... and 40 for that matter. 10mm would be pretty cool... but I think all of those calibers are executed better in the MP5 and variant platforms.
 

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I Bleed Urban Gray
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@skullbox I'm with @Mr.Maim on this. I have both platforms. My UMP9 is all German ( I have a MM kit, but haven't built it yet). I would also dare say, that I have more time shooting the UMP45 (semi) than many other amateur shooters. While others bring MP5s to... well, MP5 classes, I bring a UMP. While others bring ARs to carbine classes, I bring a UMP. While others bring CZs to PCC classes and competitions... you get the idea.

I think the perspective you are getting from Bystock, BSOE, and others above is that shooting experience of the roller-locked guns is better than that of the blowback guns in 9mm so stick to just 45 in blowback. While that is valid, the two realities are not mutually exclusive.

At the end of the day, the question is whether going 9mm in a large-format (much bigger than the Scorpion) PCC like the UMP is worth it. For me, it's a lot of fun and I always endorse people trying it. It's not the elegant, purring shooting experience of an MP5, so don't set your expectations there. It's a blow back gun with a heavier-than-necessary bolt. So you are gonna feel that bolt moving and it's going to keep you awake - just like that 45. The recoil of the 9mm is a little punchier than the 45 in the UMP, a little faster and not as thunderous as the 45. I much of my 45 suppressed and none of my 9mm suppressed (because stupid flanged 9mm barrel). Despite this, the UMP9 is a pleasure to shoot. It's not too far off from shooting the 45 UMP or USC, so if you like the feel of shooting it in 45, you'll like it in 9mm. It will not, however, mimic a roller-delayed shooting experience. The UMP is a '71 Chevy Charger, not a 2022 6-series BMW. That's the case in 45 and in 9mm.

Here's the good news. Once you go through the cost of converting the UMP to 9mm, it's easy to jump back and forth between calibers. Switching barrels takes about 10 min. If you find that you shoot the UMP in 9mm and it's just not for you, simply switch the gun back to 45 and sell your 9mm kit. They are always in demand and you will easily get your money back if it's a quality kit (i.e., not omega and not GSG9).

Also, since your motivation about converting the UMP to 9mm is to save on ammo costs, I'd think that through. I suspect cost wise, unless you shoot a bunch, the price of the 9mm conversion kit will not be offset by the savings in ammo cost for some time. But it will be a fun trip. Let us know where you land.
 

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( I have a MM kit, but haven't built it yet).

none of my 9mm suppressed (because stupid flanged 9mm barrel).

it's easy to jump back and forth between calibers. Switching barrels takes about 10 min.
Moderator, heal thyself
 

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I Bleed Urban Gray
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Moderator, heal thyself
Yea, I have to send the barrel to Adcor to get cut and threaded like we discussed, it's just not been a priority with work obligations with Delta and Omicron over the past 6 months.
 
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That said where can I find German HK made 9mm bolt + barrel or even 45 for that matter.

Use to be a bunch of bcg combos sold here haven't seen much lately :(
 
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