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BCA bolt action upper for $350? (Page 9 of 21)
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Originally Posted By HK_DUDE: Not being a dick or anything....but why is this better than a semi AR .300BLK with an adjustable gas block with a "closed" option for suppressor use? Need to see if I should change my tentative plan. So, a similar question was asked on like page 3 or so, asking why not build a straight pull bolt gun instead of using this, and the answer is about what the other guys said, but to put there's more some nuance. The biggest thing is it's designed and machined to make extraction much easier. I have 3 straight pull bolt AR uppers (.300 blk, .350 Legend, 6.5 Grendel) in addition to this BCA bolt upper, so that's my basis of comparison. Extraction is made easier by the following design features:
While extraction on .223 and .300 blk isn't terrible, some cartridges it really can be -- .458 SOCOM is always at the forefront of my mind in that regard. ETA: Additional benefits beyond easier extraction include: fewer parts/failure points, simpler operating mechanism, no fouling/cleaner operating. For legal purposes, not a semi-auto and not convertible to a semi-auto (no hole in upper for gas tube). No concerns about gas block adjustment screws locking with fouling. A closed gas block, depending on the type of gas block, can still be discharging gas loudly, and can still leak gas. Weight loss may exist, or it may be a wash with the addition of the handle. ETA 2: many edits made |
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Originally Posted By D_Man: I'm considering using one of these to make something silly.  https://www.ar15.com/media/mediaFiles/157876/Screenshot_2025-04-22_181334-3523558.png |
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Loving how mine is turning out, If only someone can make a better looking handle with a removal knob! Feel like a flat profile for the handle and not the round wire it is would look awesome and the option to thread on custom knobs would be great. |
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Originally Posted By AL1EN: Loving how mine is turning out, If only someone can make a better looking handle with a removal knob! Feel like a flat profile for the handle and not the round wire it is would look awesome and the option to thread on custom knobs would be great. |
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Originally Posted By TNRonin: I'm waiting on the relocation part. And yeah I thought about that as well, I wonder if you could get it cut and turned and threaded? Originally Posted By TNRonin: Originally Posted By AL1EN: Loving how mine is turning out, If only someone can make a better looking handle with a removal knob! Feel like a flat profile for the handle and not the round wire it is would look awesome and the option to thread on custom knobs would be great. After some range time I actually got very used to the forward short throw bolt. It would be neat to try other options but as it stands now, I am having a hard time adapting back to a regular long throw bolt action... |
Originally Posted By ar-jedi:
SO MUCH WIN IN ONE POST IT COULD CRASH ARFCOM !!!
SO MUCH WIN IN ONE POST IT COULD CRASH ARFCOM !!!
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Originally Posted By thederrick106: After some range time I actually got very used to the forward short throw bolt. It would be neat to try other options but as it stands now, I am having a hard time adapting back to a regular long throw bolt action... |
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Originally Posted By Burnsome-: Looks great How's the cycling with your bolt handle "shoe" mod working out? It slides like glass! When I first started to build the upper I carefully cycled it once and it was gritty garbage, it was sad. After I did all my mods to the BCG and my spacer it’s butter smooth. I will say i noticed the biggest difference when I polished the gas key so all edges were slippery smooth. BCG Mods 1. Stoned the gas’s key from 240-1000 grit, then polished with mother mag polish and dremmel. Then coated the gas key with dry moly lube. 2. POF roller pivot pin. 3. NiB bolt assembly. 4. 8mm spacer behind the bolt handle. |
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Originally Posted By AL1EN: It slides like glass! When I first started to build the upper I carefully cycled it once and it was gritty garbage, it was sad. After I did all my mods to the BCG and my spacer it’s butter smooth. I will say i noticed the biggest difference when I polished the gas key so all edges were slippery smooth. BCG Mods 1. Stoned the gas’s key from 240-1000 grit, then polished with mother mag polish and dremmel. Then coated the gas key with dry moly lube. 2. POF roller pivot pin. 3. NiB bolt assembly. 4. 8mm spacer behind the bolt handle. Excellent! I've installed the POF roller pin and it helped mine a little bit. Still have to push the bolt leftward as someone else mentioned earlier in this thread to make it cycle fairly smooth. Will try polishing and dry moly lube tip on the gas key that you mention. I also have a Sharps Relia-Bolt sitting in my parts bin that I'm thinking about trying Sharps Did you make your own spacer behind the bolt handle? |
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Ok, I have now read pretty much the entire thread. I am thinking 300 black out and a 9mm would be great...full time suppressed. It was brought up before.....CMMG RDB 9mm bolt and barrel. Why wouldn't that work again? That would be slick if it could. Thanks. |
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Originally Posted By HK_DUDE: Ok, I have now read pretty much the entire thread. I am thinking 300 black out and a 9mm would be great...full time suppressed. It was brought up before.....CMMG RDB 9mm bolt and barrel. Why wouldn't that work again? That would be slick if it could. Thanks. 9mm would be the bomb. I'm in for the RKI's to chime in on this one. |
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Originally Posted By Burnsome-: Excellent! I've installed the POF roller pin and it helped mine a little bit. Still have to push the bolt leftward as someone else mentioned earlier in this thread to make it cycle fairly smooth. Will try polishing and dry moly lube tip on the gas key that you mention. I also have a Sharps Relia-Bolt sitting in my parts bin that I'm thinking about trying Sharps Did you make your own spacer behind the bolt handle? I made my spacer with scrap plastic and files. User VTD 3d printed me some and there on the way. |
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This is my final iteration, waiting on the bolt handle relocation. Attached File |
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Originally Posted By HK_DUDE: Ok, I have now read pretty much the entire thread. I am thinking 300 black out and a 9mm would be great...full time suppressed. It was brought up before.....CMMG RDB 9mm bolt and barrel. Why wouldn't that work again? That would be slick if it could. Thanks. The RDB bolt's rear face edges would be the only issue. IIRC, the RDB bolt doesn't rotate quite as far as a standard AR bolt in the CMMG carrier, creating a slight misalignment. Again, IIRC, I think this is done with the cam path. This misalignment puts the leading edge of the lugs on the barrel lined up midway through the angled lug of the RDB bolt rear. In the BCA carrier, one of two things would occur: 1) the bolt would be rotated fully shut, and the full force of the recoil would be transferred from the rear edges of the bolt lugs into the faces of the barrel lugs. This is not how the bolt was intended to be used, but may be able to handle that pressure. I'd expect the rear edges of the bolt lugs to eventually/slowly wear down flatter, or could crack. Or nothing could come of it as they're not high pressure rifle rounds. 2) the carrier/bolt aren't fully closed. Upon firing, the handle rotates upward on its own, and the carrier retracts... with no spring to slow it down. Rotation is gonna take a lot more energy than in the RDB setup (on account of also needing to spin the carrier and the handle, which has a lot of weight far from the center of rotation. So, maybe it rotates and barely causes any retraction. Maybe it sends it flying to the back of the receiver. Those seem like the downsides I can think of, but I'm sure someone with more experience with those uppers could offer more insight. If you can find or get modified a standard AR bolt to have the right face diameter for a 9mm, I think that should work with one of their barrels. Alternatively, you could contact someone like Rudy at Macon Armory -- he specializes in .45 ACP DI PCCs (not blowback), but does other calibers -- and source a bolt and barrel there. I know you could get a .45 ACP or 10MM bolt and barrel from him to do a bolt gun, as I've inquired. Not if he could do a 9mm barrel and bolt like that, or if it'd be outside his work. |
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Originally Posted By TNRonin: This is my final iteration, waiting on the bolt handle relocation. https://www.ar15.com/media/mediaFiles/13145/IMG_20250423_142353_jpg-3524622.JPG That's slick. |
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Originally Posted By HK_DUDE: Ok, I have now read pretty much the entire thread. I am thinking 300 black out and a 9mm would be great...full time suppressed. It was brought up before.....CMMG RDB 9mm bolt and barrel. Why wouldn't that work again? That would be slick if it could. Thanks. Blowback or delayed blowback would require you to hold the bolt manually closed when firing, no? I don't see how the factory BCA setup would function correctly in a system designed to work without a gas tube in the first place... |
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Originally Posted By PreacherOfGadget: That's slick. The way I understand it the RDB system is dependent on the carrier group and the bolt. You can use it with any 9 mm barrel that has the AR-15 locking system. But the whole purpose of the RDB is to work with the semi-automatic movement there would be no point in having the RDB system because it's towards the release of the locking. Where is the BCA bolt gun is the opposite. Interestingly, yesterday while I was shooting, and then a couple of my students, I noticed that at the end of the locking stroke you could feel it engaging the extractor onto the round. Attached File Attached File In fact you could use the click and jump onto the rim as an indicator that it was ready to finish the movement of the locking process. I got to play with that a little bit more. And the motion pattern is starting to become more fluid. I don't have near the issues of closing the bolt I had with the 5.56 barrel. But I never felt the extractor going over the rim of the 5.56. Maybe the head spacing, or freebore has some bearing on that particular 5,56 barrel. These are just data points that I use when operating the gun. |
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Originally Posted By HK_DUDE: Ok, I have now read pretty much the entire thread. I am thinking 300 black out and a 9mm would be great...full time suppressed. It was brought up before.....CMMG RDB 9mm bolt and barrel. Why wouldn't that work again? That would be slick if it could. Thanks. On another thread about the why no love for the CMMG RDB, it was discussed about 9 mm barrels. Once the correct bolt size to match up with a 9 mm, getting a barrel is a no-brainer. And it would be pretty neat to have a 9 mm bolt action suppressed. But the way I understood it the 300 blackout was designed to replace the 9mm MP5. I think the only value to having a 9 mm suppressed bolt gun is cost of ammunition? |
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Originally Posted By AL1EN: Agreed the ammo cost of 9mm would be nice. But ain't that the benefit of a bolt gun? You can shoot more expensive ammo conservatively and reducing cost over fewer round count. 
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When you can feel every part of the cycling, like the extractor clicking over the rim of the case, it really helps understanding what is happening while it cycles. The more polished all the parts are, the smoother running it is, the more you can feel all of that. I like that tactile feedback. I gotta say, I would be curious to hear or read about the volume difference between 9mm suppressed subs and 300 blk suppressed subs in bolt guns. I could see the suppressed 9mm bolt gun being better than .300 BLK for pest removal in areas that aren't completely rural. Less over-penetration risk. Probably still a lot better of solutions in most situations, but 'tis a valid use case. Cheaper ammo is cheaper ammo, and that makes sense. While the bolt gun stretches your dollar's value on .300 blk, 9mm would be stretch it much further. Different financial situations could make for that being a wise choice. I'm a big fan of starting new shooters on soft shooting cartridges. While 5.56 and .300 BLK aren't hard hitters, 9mm is even less so. 9mm in a bolt upper to learn and practice with, especially for a kid, and would be a great stepping-stone to most AR-15 length cartridges. (A few of the hard-hitters like .458 SOCOM, .450 BM, & .50 Bewoulf might be a bit big step, lol.) I'd think extraction would also be very, very easy with the short case. The ability to have multiple uppers on the same lower, sharing identical ergonomics -- I like that, especially for new shooters. If you're working on training out a flinch, too, working with lower recoil setups is awesome. You get all the sensory feedback, but less intense. |
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Originally Posted By PreacherOfGadget: When you can feel every part of the cycling, like the extractor clicking over the rim of the case, it really helps understanding what is happening while it cycles. The more polished all the parts are, the smoother running it is, the more you can feel all of that. I like that tactile feedback. I gotta say, I would be curious to hear or read about the volume difference between 9mm suppressed subs and 300 blk suppressed subs in bolt guns. I could see the suppressed 9mm bolt gun being better than .300 BLK for pest removal in areas that aren't completely rural. Less over-penetration risk. Probably still a lot better of solutions in most situations, but 'tis a valid use case. Cheaper ammo is cheaper ammo, and that makes sense. While the bolt gun stretches your dollar's value on .300 blk, 9mm would be stretch it much further. Different financial situations could make for that being a wise choice. I'm a big fan of starting new shooters on soft shooting cartridges. While 5.56 and .300 BLK aren't hard hitters, 9mm is even less so. 9mm in a bolt upper to learn and practice with, especially for a kid, and would be a great stepping-stone to most AR-15 length cartridges. (A few of the hard-hitters like .458 SOCOM, .450 BM, & .50 Bewoulf might be a bit big step, lol.) I'd think extraction would also be very, very easy with the short case. The ability to have multiple uppers on the same lower, sharing identical ergonomics -- I like that, especially for new shooters. If you're working on training out a flinch, too, working with lower recoil setups is awesome. You get all the sensory feedback, but less intense. I was just giving them the suppressor experience. Because of all the noise and whatnot, this changes their perspective. I was shooting both this 300 blackout build, and a CMMG banshee build I just finished. One really like the banshee the other one wouldn't shoot it. The lady that went before this one she gladly took magazine from me and shot another magazine out of it. But this thread's not about the CMMG. I think for the price the BCA bolt gun is in excellent upper to have. |
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| I meant all my rambling in regards to the idea of a 9mm in BCA's bolt upper, not in regards to CMMG's products in specific or in regards to your training of someone, though admittedly I can see how some of it could apply. I've got a couple of nieces, one whose coming up on learning to shoot soon, so it's another lens I view gun builds through. |
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Attached File Attached File Attached File Paladin did a good job. Going to get the rest of the gun back together in the morning and see how it feels/operates. |
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Originally Posted By VTD: https://www.ar15.com/media/mediaFiles/26478/IMG_0560_jpeg-3524926.JPG https://www.ar15.com/media/mediaFiles/26478/IMG_0561_jpeg-3524928.JPG https://www.ar15.com/media/mediaFiles/26478/IMG_0562_jpeg-3524929.JPG Paladin did a good job. Going to get the rest of the gun back together in the morning and see how it feels/operates. |
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Originally Posted By D_Man: Looks good! One small suggestion, for the screws with tips pointing out, try shortening them a bit and using acorn nuts on them to give a bit more finished look. Attached File |
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Originally Posted By VTD: I would absolutely love a bolt action 9mm upper. Since then, I make my own CMMG RDB compatible barrels which also work if you want to do a bolt action build: https://c3junkie.com/?page_id=1882 I have one for sale on Gunbroker right now and some others on hand BTW.  The issue is that with the short 9mm case that ejection is an issue as the spent case wants to flop out right after it clears the chamber. Here is a thread on Reddit discussing it: https://www.reddit.com/r/guns/comments/1jxrk8r/comment/mn1jlnv/?context=3 I am considering getting a BCA upper to try this myself and modify it for a fixed ejector like I have done in the past for the CMMG Banshee. However, I am waiting for them to get their 450BM kit to come back in stock as I want to do a bolt action in .45ACP. vs buying their 556/300BLK kit when I have a bunch of those bolts already laying around. |
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I'm sold on the bolt action idea. When funds allow, I will order the upper/bolt action BCA for 5.56/300. I currently have 4 different 300 barrels, so I can play around alot. I will build a 300 first, then see if a 9mm will be next. I have a CMMG 9mm built and can try that barrel. May start to look for a 5.45 bolt sooner than later, if the factory 9mm CMMG RDB bolt won't work. I have just dipped my toe into the suppressor world. Bought a SiCo Spectre 9mm TI. So far, it does better on 9mm than 300, but still playing with loads. I reload everything. For me, the 9mm seems less expensive to load and play with super soft and quiet loads. I am just playing so ballistics don't really mean much for this project. |
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Just finished my build, the flat trigger I order got here today and had two different springs. The yellow ones seem super light and feels great but I’m curious on light primer strikes. Hoping to go shoot tomorrow and will give my honest opinion if money is well spent on this build. https://ar15discounts.com/products/dirty-bird-industries-single-stage-nickel-teflon-trigger-group/ |
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Geeez, I could dig in on doing a 9mm, a .45 ACP, or if there were the parts available, .357 Mag sounds cool. I know how quiet my .357 lever gun is running .38 spl; so, I have to imagine a bolt gun would be about as quiet, presuming the barrel isn't stupid short. I'm reading the words in these posts, and I'm feeling myself being poorer, lol. Too many fun projects here. |
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Originally Posted By PreacherOfGadget: Geeez, I could dig in on doing a 9mm, a .45 ACP, or if there were the parts available, .357 Mag sounds cool. I know how quiet my .357 lever gun is running .38 spl; so, I have to imagine a bolt gun would be about as quiet, presuming the barrel isn't stupid short. I'm reading the words in these posts, and I'm feeling myself being poorer, lol. Too many fun projects here. 158gr 38 special is almost Hollywood quiet out of a 10”+ barrel with a can, but you get full powder burn and power on 357 loads. Do I need one? No. Do I want one? Yup. |
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Originally Posted By HK_DUDE: May start to look for a 5.45 bolt sooner than later, if the factory 9mm CMMG RDB bolt won't work. You can get cheap 5.45 bolts here: https://www.redxarms.com/Bolts-s/1876.htm One thing to note is that the CMMG RDB bolts do have the bottom two bolt lugs closer to together to clear the feed lips of Glock mags. So a 5.45 bolt isn't going to work with Glock mags. I would just use Endomags or better yet an Exomag like seen below. One of the lower capacity mags would probably be great for a bolt action build.  |
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Originally Posted By amphibian: I don't understand why you want to try to use the CMMG RDB bolt for a bolt action. The angled lugs on the bolt combined with the cam pin path are going to try to cycle the action. You need a 5.45 bolt which has the correct size bolt face and traditional squared off bolt lugs so that the bolt is locked when the round detonated. You can get cheap 5.45 bolts here: https://www.redxarms.com/Bolts-s/1876.htm One thing to note is that the CMMG RDB bolts do have the bottom two bolt lugs closer to together to clear the feed lips of Glock mags. So a 5.45 bolt isn't going to work with Glock mags. I would just use Endomags or better yet an Exomag like seen below. One of the lower capacity mags would probably be great for a bolt action build. https://www.meanarms.com/uploads/images/ExoMag%20Banner_8bfe156bf9e7.jpg Well now I want to build a 9mm bolt action rifle! No sbr in NY or cans, but 9mm is my primary handgun round and I am setup to reload it sooooo..... |
Originally Posted By ar-jedi:
SO MUCH WIN IN ONE POST IT COULD CRASH ARFCOM !!!
SO MUCH WIN IN ONE POST IT COULD CRASH ARFCOM !!!
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Originally Posted By amphibian: I don't understand why you want to try to use the CMMG RDB bolt for a bolt action. The angled lugs on the bolt combined with the cam pin path are going to try to cycle the action. You need a 5.45 bolt which has the correct size bolt face and traditional squared off bolt lugs so that the bolt is locked when the round detonated. You can get cheap 5.45 bolts here: https://www.redxarms.com/Bolts-s/1876.htm One thing to note is that the CMMG RDB bolts do have the bottom two bolt lugs closer to together to clear the feed lips of Glock mags. So a 5.45 bolt isn't going to work with Glock mags. I would just use Endomags or better yet an Exomag like seen below. One of the lower capacity mags would probably be great for a bolt action build. https://www.meanarms.com/uploads/images/ExoMag%20Banner_8bfe156bf9e7.jpg Originally Posted By amphibian: Originally Posted By HK_DUDE: May start to look for a 5.45 bolt sooner than later, if the factory 9mm CMMG RDB bolt won't work. You can get cheap 5.45 bolts here: https://www.redxarms.com/Bolts-s/1876.htm One thing to note is that the CMMG RDB bolts do have the bottom two bolt lugs closer to together to clear the feed lips of Glock mags. So a 5.45 bolt isn't going to work with Glock mags. I would just use Endomags or better yet an Exomag like seen below. One of the lower capacity mags would probably be great for a bolt action build. https://www.meanarms.com/uploads/images/ExoMag%20Banner_8bfe156bf9e7.jpg I want to try the CMMG bolt and barrel, simply because I have one. Didn't think it would hurt to throw it and manually check it. If it is a sure "no go", I won't bother. I am using CMMG gen 2 9mm AR mags. |
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| The problem with using the CMMG RDB bolt is the best result you could hope for is a setup where you use an overpriced bolt that is going to wear/break faster than a normal bolt because all the force that's normally distributed over 5 flat surfaces is instead applied to 5 edges, and as a result applies a much greater force in those areas because it is concentrated. You risk damaging or destroying the bolt. Spend the $60+shipping for the 5.45 bolt to be safe. This is a time when it's worth the money. |
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Originally Posted By PreacherOfGadget: The problem with using the CMMG RDB bolt is the best result you could hope for is a setup where you use an overpriced bolt that is going to wear/break faster than a normal bolt because all the force that's normally distributed over 5 flat surfaces is instead applied to 5 edges, and as a result applies a much greater force in those areas because it is concentrated. You risk damaging or destroying the bolt. Spend the $60+shipping for the 5.45 bolt to be safe. This is a time when it's worth the money. Thanks. The more I research, maybe the stowaway pistol with a brace in 9mm would fit the bill better. Still do the BCA for 300. After realizing that my 9mm can isn't too great on 300, the 9 has went to the top of the list. |
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Range report: Only had 20 rounds to play with but it was a smooth shooter. Did notice that you have to mind the force you use chambering a round. To light and you have to back the bolt up a little bit and push the round forward again. I wouldn’t have even tried to shoot this rifle without the bolt mod’s performed. Grouped well I would say, less than 1.5” out of a 7.5 barrel at 50 yards. I can bring that in tighter with a rest. sighted it for 50yards with a 4x scope, just think 100yards would be a lot for this pistol. All said and done it’s a fun range toy. 
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Originally Posted By HK_DUDE: Thanks. The more I research, maybe the stowaway pistol with a brace in 9mm would fit the bill better. Still do the BCA for 300. After realizing that my 9mm can isn't too great on 300, the 9 has went to the top of the list. |
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Originally Posted By VTD: I wish they made a repeater. Originally Posted By VTD: Originally Posted By HK_DUDE: Thanks. The more I research, maybe the stowaway pistol with a brace in 9mm would fit the bill better. Still do the BCA for 300. After realizing that my 9mm can isn't too great on 300, the 9 has went to the top of the list. Absolutely agree. Maybe a guy can cut a window and jam a glock mag in...haha. |
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A few different 556 and one 7.62x39 complete uppers (16") are down to $219.95. I couldn't get a coupon code to work but after $10 shipping and tax I was right around $250. I probably didn't need another one but ordered a 556 for future build use anyways. Attached File |
Originally Posted By ar-jedi:
SO MUCH WIN IN ONE POST IT COULD CRASH ARFCOM !!!
SO MUCH WIN IN ONE POST IT COULD CRASH ARFCOM !!!
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Originally Posted By thederrick106: A few different 556 and one 7.62x39 complete uppers (16") are down to $219.95. I couldn't get a coupon code to work but after $10 shipping and tax I was right around $250. I probably didn't need another one but ordered a 556 for future build use anyways. https://www.ar15.com/media/mediaFiles/140266/Screenshot_2025-04-30_080842_jpg-3529492.JPG Damn. That's approaching the price of just an upper and a gas block/shaft collar. |
BCA bolt action upper for $350? (Page 9 of 21)
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