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Posted: 3/20/2024 10:32:07 PM EDT
https://cmmg.com/barrel-and-bcg-kit-8-4140cm-sbn-9mm
Looking to build an upper off the kit above. It says it fits standard AR uppers with a "modified ejection port." How does the ejection port need to be modified? Can I use a standard AR upper with a 9mm defector and dust cover? |
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USA
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Posted: 3/21/2024 6:10:47 AM EDT
[#1]
They’re referring to an enlarged ejection port. Yes, many use regular uppers and they still seem to work fine.
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MI, USA
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Posted: 3/21/2024 9:56:18 AM EDT
[#2]
Quote HistoryOriginally Posted By CJofFL: They’re referring to an enlarged ejection port. Yes, many use regular uppers and they still seem to work fine. And CMMG is not the only manufacturer that indicates that an "enlarged" ejection port is suggested?, needed?, desirable?, cool to have? ... for PCCs. And when a manufacturer says "enlarged" do they mean taller, wider, both taller and wider, with an oval shape, with a teardrop shape? Why do manufacturers think that everyone is a mind reader? Responses from manufacturers are respectfully requested. Responses from non-manufacturers will be considered guesses, opinions, wishful thoughts, musings, anecdotal experiences where 'YMMV' applies, etc. MHO, YMMV, etc. Be well. |
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IN, USA
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Posted: 3/21/2024 10:29:39 AM EDT
[#3]
I built mine with an aero precision xl upper receiver as the xl means enlarged ejection port, rest of receiver is same as any other.
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VA, USA
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Posted: 3/21/2024 11:16:59 AM EDT
[#4]
The XL uppers just trim a little extra metal along the top and front of the ejection port. You can take a dremel from a spot just to the right of where the ejection port cover detent locks in and trim around the corner to the bottom front of the door-like 12:30 to 4:00. This is all behind the dust cover so you will not see it when it's closed.
It is not necessary for a 9mm though. It can help with the larger calibers. |
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USA
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Posted: 3/21/2024 1:46:30 PM EDT
[#5]
Quote HistoryOriginally Posted By SecondAmend: Responses from manufacturers are respectfully requested. Responses from non-manufacturers will be considered guesses, opinions, wishful thoughts, musings, anecdotal experiences where 'YMMV' applies, etc. In my anecdotal experience, you'd be better off asking the manufacturer directly  |
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MI, USA
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Posted: 3/21/2024 3:02:00 PM EDT
[#6]
Quote HistoryOriginally Posted By CJofFL: In my anecdotal experience, you'd be better off asking the manufacturer directly Quote HistoryOriginally Posted By CJofFL: Originally Posted By SecondAmend: Responses from manufacturers are respectfully requested. Responses from non-manufacturers will be considered guesses, opinions, wishful thoughts, musings, anecdotal experiences where 'YMMV' applies, etc. In my anecdotal experience, you'd be better off asking the manufacturer directly My point is that one should not have to waste their time and the manufacturer's time asking and answering. The manufacturers should just put the information in their ads. For example, car makers tell us exactly what oil to put in our engine, not simply, "use oil that's good". MHO, YMMV, etc. |
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USA
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Posted: 3/21/2024 4:31:56 PM EDT
[#7]
Ok, then.
Originally Posted By SecondAmend: And CMMG is not the only manufacturer that indicates that an "enlarged" ejection port is suggested?, needed?, desirable?, cool to have? ... for PCCs. And when a manufacturer says "enlarged" do they mean taller, wider, both taller and wider, with an oval shape, with a teardrop shape? For CMMG: Suggested. I already answered the needed question above- many do not use them. Desirable or cool to have is up to you. Taller and you can see the difference in pics. |
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Posted: 3/21/2024 4:47:39 PM EDT
[#8]
Thanks guys, seems like an aero xl upper should do the trick.
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IN, USA
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Posted: 3/22/2024 6:05:05 PM EDT
[#9]
Quote HistoryOriginally Posted By BuckeyeRifleman: Thanks guys, seems like an aero xl upper should do the trick. 
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