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Posted: 11/22/2025 12:25:34 PM EDT
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Reposting this in the correct forum section Wanting to build a new 9mm RDB upper to go on my CMMG lower. Im thinking about going side or front charging and a receiver without a rear charge handle. Trying to minimize gas when suppressed. budget is a concern because its an upper not normally going to be used. tying to keep handguard 7-8" long because the CMMG barrel will be 8". i dont think i will mind if the handle reciprocates or not I liked the Type Zero front charging handguard but its not available yet in 7.5" and i still need a receiver. I have also considered getting a side charging BearCreek 556 upper and converting it to 9mm RDB because the uppers are soo cheap. i would assume i can change the bolt for 9mm RDB. are there other any options that would be better? does the side/front charging uppers make a significant enough change in reducing gas? i might consider doing this to a couple others such as a .300 and my BRT CAR15SD because they could use some gas reduction |
| Assuming you go with the Fixed Ejector version, left side charging isn’t an option. I built a couple of Gibbz side-charging uppers with the older plunger ejector parts - they worked OK if you changed the ejector spring when it wore out. I’d be open to selling if you can’t find the parts anywhere else. |
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i think ill stick with the old plunger style ejector just because its cheaper. and ill do right side charge so gas wont blow in my face right now my plan is to order a cheap BearCreek 300 8.5" upper right side charger, its on Black friday special for $160 and if i cant convert it to 9mm, at least i have a extra 300 upper https://www.bearcreekarsenal.com/300-blackout-8-5-parkerized-hb-1-8-twist-pistol-5-3-handguard-scg2-nrail-upper.html i can find the complete 9mm CMMG 8" barrel+ BCG kit ill go that route. but doesnt seem like its offered anymore, probably cause the upgraded fixed extractor. But places still have it. hopefully i can just swap the bolt head and maiby the weight if there iso ne to the 300 BCG i think i have a couple 7.5" handguards laying around or ill jsut buy another 8". i really like using 8" handguard cause the tri-lug adapter for the can adds half inch and i like minimal gap am i missing something? |
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Originally Posted By Kingfish999: i think ill stick with the old plunger style ejector just because its cheaper. and ill do right side charge so gas wont blow in my face i can find the complete 9mm CMMG 8" barrel+ BCG kit ill go that route. but doesnt seem like its offered anymore, probably cause the upgraded fixed extractor. But places still have it. hopefully i can just swap the bolt head and maiby the weight if there iso ne to the 300 BCG Link to my site with 2 different fixed ejector CMMG RDB builds I did https://c3junkie.com/?page_id=2747 Let me know if I can help.  |
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I'm wondering if you could just buy a foxtrot mike 9mm complete upper with a forward charging handle on the handguard, disassemble it, then reassemble it with your barrel/RDB BCG. You then sell the FTM BCG/barrel for $125-$150. Primary arms have them available that uses a 7 inch barrel.... but the handguard is 8.75 inches long.  OR....maybe call/contact them, and ask if they will sell you just the upper receiver, handguard, and the charging system. . |
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Originally Posted By IdahoPCCinc: I'm wondering if you could just buy a foxtrot mike 9mm complete upper with a forward charging handle on the handguard, disassemble it, then reassemble it with your barrel/RDB BCG. You then sell the FTM BCG/barrel for $125-$150. Primary arms have them available that uses a 7 inch barrel.... but the handguard is 8.75 inches long. https://image.primaryarms.com/production/SSP%20Applications/NetSuite%20Inc.%20-%20SCA%20Mont%20Blanc/Development/img/PA-FM9-8.5UPR-7IN_01.jpg?resizeid=7&resizeh=1100&resizew=1100 OR....maybe call/contact them, and ask if they will sell you just the upper receiver, handguard, and the charging system. . here is another pic from my site:  |
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Originally Posted By Sailormilan2: The upper really doesn't care what barrel you use. I would get a Bear Creek upper, hopefully with a Black Friday sale, or, get one of their side charge upper and bolt. Then use whatever barrel I decided on. Also note that you need an upper thick enough so that when you do mill the relief it doesn't break through the other side. |
| Trying to make the obsolete and unreliable plunger ejector system work with a side charger is a lot of work just to address the gas-in-face issue. My recommendation would be to start with the current FE system and do the RTV sealant mod to the charging handle. |
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Originally Posted By amphibian: You are correct that it doesn't care on the barrel but it MIGHT matter on what RDB carrier he uses. As I posted above, the FM uppers are NOT clearanced for any cam pin relief. I machined a cam pin relief for the FE Banshee / Dissent carrier which is also further back than the standard AR cam pin relief location which BTW is what the old spring loaded ejector Banshee uses. Also note that you need an upper thick enough so that when you do mill the relief it doesn't break through the other side. I guess I should have been a bit more specific. I just had a blowback in mind. Sorry about that. |
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in my BRT CAR15SD (9mm RDB integrally suppressed), i never had any issues with ejecting with the plunger ejector. its main issue seems to be FTF every now and then. it hated Endomags but seems mostly alright using colt mags Originally Posted By StealthyBlagga: Trying to make the obsolete and unreliable plunger ejector system work with a side charger is a lot of work just to address the gas-in-face issue. My recommendation would be to start with the current FE system and do the RTV sealant mod to the charging handle. ive done the RTV mod in all my rifles. they still seem to be abit gassy. also i feel like the side charging is something different to try. my CAR15SD is very gassy and unpleasant rapid fire. my AR45 isnt bad without its suppressor but gets some with its can. id rather use a reciever i dont have to grind for the cam pin. tho i know i can easilly do it id just rather start with one already done. but is the FM upper worth using over the BCA? it does look nice |
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i guess an issue with the Foxtrot Mike front charge is that the minimum handgaurd lenght is 8.75". So i would need to buy a 16" CMMG barrel and have it cut. and im assuming i would need to do the Dissent BCG and do a fixed extractor. all in all i think this is getting in too deep for something i dont use alot ill accept the plunger ejector and probably still do the BCA upper and convert it to RDB |
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Originally Posted By Kingfish999: i guess an issue with the Foxtrot Mike front charge is that the minimum handgaurd lenght is 8.75". So i would need to buy a 16" CMMG barrel and have it cut. Originally Posted By Kingfish999: i guess an issue with the Foxtrot Mike front charge is that the minimum handgaurd lenght is 8.75". So i would need to buy a 16" CMMG barrel and have it cut. and im assuming i would need to do the Dissent BCG and do a fixed all in all i think this is getting in too deep for something i dont use alot ill accept the plunger ejector and probably still do the BCA upper and convert it to RDB |
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i know its gonna be more than i really want to spend. and im already getting to a point i could just buy a Dissent upper. how much would you want to build me an upper? i dont need to worry about bufferless since my primary upper uses it. 10.5" barrel is perfectly fine if you happen to have a 9.5-10.25" handguard otherwise how much for one of those barrels? is there a place to buy these barrels? i only see the 5, 8, and 16 inch sold despite them selling the 6.5 and 10.5 uppers i dont shoot much at all. handfull of times a year and maybe only 50-200 rounds per rifle. so i never noticed issues with ejection of my two plunger RDB setups. the CAR15SD just gets an occasional FTF that i i never found the cause, but the Colt mag lower works significantly better than the milspec lower with Endomags which would FTF every 1-3 rounds. random other question: on my RDB AR45 using CMMG lower, the LRBHO activates EVERY shot. when cycled by hand it works flawlessly but some reason shooting it makes it trip every round. if i hold the release when shooting its perfect. i have since removed the linkage for it so its not an issue but would be nice to have. any idea what might cause that? |
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Originally Posted By Kingfish999: random other question: on my RDB AR45 using CMMG lower, the LRBHO activates EVERY shot. when cycled by hand it works flawlessly but some reason shooting it makes it trip every round. if i hold the release when shooting its perfect. i have since removed the linkage for it so its not an issue but would be nice to have. any idea what might cause that? However, if you look at my link, I'm using an MGI lower w/ their Grease Gun magwell and GG mags do not have LRBHO so I can't comment on your issue. I'm guessing that the carrier is bottoming out in the buffer tube and jolting the BHO to engage so maybe a stronger BHO spring would help....again just a guess since I don't run a CMMG .45 Glock lower. I'll send you a PM on the other topics. |
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i cheaped out and ordered a BearCreek 556 side charge upper. Didnt want to deal with modifying the FoxMike for the cam pin. Ill buy a 10.5" RDB barrel and a CMMG 9mm bolt repair kit. Im assuming i should be able to use the Foxtrot Mike Mike9 Gen 1 handguard with a standard AR9 upper. or am i wrong about that |
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Got the BCA upper today. my first side charger and its pretty cool. intrested how it will shoot in 556 11.5" barrel before i disassemble its for parts did try and swap my existing 9mm RDB bolt into the side charge carrier and it does not fit. looks like ill need to open the hole where the gas rings go in order to fit the 9mm bolt can i not post pics on this forum without using an image host site? |
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just an update for anybody who sees this and wants to do something similar. all my plans fell apart pretty quickly despite ordering way too many upper stuff. could have just bought a CMMG Dissent but now i have soo much more knoweldge and parts to upgrade my other PCCs. original plan was use the BearCreakArsenal 556 reciprocating upper and swap a CMMG 9mm RDB bolt into the carrier. found out pretty fast the CMMG bolt will not fit a standard carrier. I had to use a lathe to narrow a section of the CMMG bolt to fit inside the carrier. Then i had to use a carbide bit to enlargen the hole larger for the stem of the bolt so the spring the CMMG uses will fit. https://i.postimg.cc/CLDNt9Zm/85df37bd-3f07-4687-b55e-00ff94fbb8fa.jpg after that i thought i had it done and went to test cycle the upper to find the BCG basically locked solid. after mortar clearing it to open it, i realized that a fundemental flaw i overlooked was the cam pin track on the CMMG is very different than a standard AR15 BCG. it makes the bolt rotated too much where it cams the angled lugs of the CMMG. the standard AR bolt also extends further out and retracts further in than the CMMG https://i.postimg.cc/tsNjj8MV/20260121-192809.jpg https://i.postimg.cc/75nkkjWH/20260121-192512.jpg https://i.postimg.cc/w1QppnGm/20260121-192633.jpg since i have no way of reworking the cam pin track, i completly abandoned that side charger upper and made it into my 300blk upper to see if it reduces gas to the face. |
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next attempt was using a FoxtrotMike 9mm upper front charger upper and convert it to RDB using the older plunger ejector. Even bought stuff to do a second front charger handguard on second PCC. As Anphibian warned me and had pictures of, the FM front charger handguard needs the charge lever slot extended when used with the RDB. cutting the slot longer didnt come out very pretty but it is functional. there is a fine line cutting the slot too far and not enough. too far and the rail looses support and makes it have a bump as it realigns and makes it less smooth. too short and the bolt hold open wont activate. the first handguard i modified i went quite abit too far, the second one is right on the line of being perfect https://i.postimg.cc/63nrSvqJ/20260202-193838.jpg Anphibian also mentioned cutting some of the return spring because it becomes solid before the bolts far enough backwards. i had to almost cut my spring in half to get it to lock the bolt open. i streched the spring best i can but it will never be long enough. but i dont think it will be an issue for me. i also had to mess around with the rod length to contact the BCG. the seperate rod i ordered was too long and i had to shorten it a good amount. one rod was too short and i had to weld on an extenshion. again rod length became very picky as too long would hold bolt open, too short would not engage hold-open i used a dremel to grind out a cam pin recess in the FM 9mm upper which actually wasnt very hard to do with a carbide bit. everything was working fine so i took it to range and it was plauged with non stop ejection issues. basicly caould only get off 1-2 shots at a time before it would jam. i dont blame the plunger ejector for this, i blame the ejection port opening for this and i suspenct this is why people want to convert to fixed ejectors. i have never had issues with the ejection on my other 9mm or 45 RDB setups but this use full size ejection ports. |
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so now i sprung for a Gibbs side charging non-recip upper that i got today. it is what i should have gone with in the beginning. i swapped that into my old 9mm with no issues because it will benefit the most from it. its intregral suppressor prevents front charge and it has the most gas i nthe face when shooting. for this new 9mm, i went ahead and ordered the CMMG fixed ejector retrofit kit since i still needed a RDB BCG and receiver. i might modify it to use a FM front charge handguard. all i have to do is drill a hole for the charge handle rod. i already ground of the lug of the handguard that locks into a FM receiver rebuilt the FoxtrotMike 9mm blowback upper and ordered a lower for it so ill have a good comparison of RDB vs Blowback 9mm. |
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Originally Posted By Kingfish999: amphibian and FoxtrotMike confirmed that their front charge handguards do not fit standard AR uppers. has to be a Mike9 receiver. so i guess im just gonna stick with side charging for now. It only takes a little modification to the upper. The charging handle only rides around 1/8" higher than a gas tube.   That's it. I used it to do a couple of .22lr builds.   You may need to mod your charging handle, depending on how the charging rod interacts with the gas key. (Either to allow clean pass through of the charging rod to contact the carrier's key, or plug the CH hole so the front charging handle pushes the standard charging handle which pushes the bolt. (The charging handle's catch will also need to be modified in the second approach. You may also need to alter the length of your forward charging handle's action rod, too. (I think that's their term...) I've not adapted one to a 9mm build in a standard upper, but the process is the same. |
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