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Posted: 8/23/2026 8:50:40 PM EDT
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Hi all. I am thinking of buying the Daniel Defense M4A1 upper from Brownells. This upper has a FSP. I typically change the gas tube to reduce/fine tune gas. With this specific upper, does anyone know if I am able to pull the gas tube out through the upper receiver? I don't see any other way of changing the gas tube without having to unpin the FSP, which I rather not do. Has anyone removed a gas tube this way before? Since the gas tube is angled, I assume you would need to rotate the gas tube as you pull it out -- and then rotate it while you insert it back in. I have not found any videos or photos of this method, but it's the only thing I can come up with that would allow a swap without unpinning the FSP. |
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You do not need to remove the front sight post to swap out the gas tube Drive out the gas tube pin in the fsb with a punch. The tube will go back into the receiver and inch or so, and can then be pulled out past the fsb at an angle. |
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Tap out gas tube retaining pin in fsb. Simply slide the gas tube out of the fsb and into the upper receiver until it clears the fsb. Twist the gas tube a bit so it's offset from the fsb, and just pull it out of the upper receiver. Do the above in reverse to install new gas tube. |
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Yeah you would need to wiggle it around in some odd angles. However it is not tat difficult to drive the pins out of the fsp too. Just remember the orientations and which pin was the front vs rear. Then just tap those suckers back in once you're ready to go. Since the pins are tapered a little, it will seat just fine and won't need to be replaced like roll pins that you might take out. |
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Originally Posted By flcracker: I'm curious how changing the gas tube helps to reduce/fine tune gas..... 🤔 Not a common thing to do but yes it’s a thing. https://blackrivertactical.com/WP/BRT-EZTUNE-Gas-Tube-Configurable-Carbine-p103167251 |
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Originally Posted By NachoDip: Not a common thing to do but yes it’s a thing. https://blackrivertactical.com/WP/BRT-EZTUNE-Gas-Tube-Configurable-Carbine-p103167251 I have BRT’s on 3 suppressed guns. They are fantastic! |
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Originally Posted By flcracker: I'm curious how changing the gas tube helps to reduce/fine tune gas..... 🤔 https://blackrivertactical.com/WP/Adjustable-Gas-System-c6464009 |
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Originally Posted By NachoDip: Not a common thing to do but yes it’s a thing. https://blackrivertactical.com/WP/BRT-EZTUNE-Gas-Tube-Configurable-Carbine-p103167251 Cool! Learn something new every day! |
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Originally Posted By THEdtw: Normal FSP with carbine handguards, totally doable. If you're looking at the RIS II upper, which I assume you are, I do not believe it would be possible without being able to move the FSP. Yeah, RIS II makes routine stuff not so routine. I had no experience installing one of those handguards until recently. I had no idea the front sight had to be removed. It wasn't difficult as I had experience doing that but it was a surprise that I had too. |
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Originally Posted By HobbitHunter: Tap out gas tube retaining pin in fsb. Simply slide the gas tube out of the fsb and into the upper receiver until it clears the fsb. Twist the gas tube a bit so it's offset from the fsb, and just pull it out of the upper receiver. Do the above in reverse to install new gas tube. This makes perfect sense, but would it work on the RIS II handguard? Seems like the clearance is a lot less forgiving. |
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Originally Posted By dalle0001: Yeah you would need to wiggle it around in some odd angles. However it is not tat difficult to drive the pins out of the fsp too. Just remember the orientations and which pin was the front vs rear. Then just tap those suckers back in once you're ready to go. Since the pins are tapered a little, it will seat just fine and won't need to be replaced like roll pins that you might take out. Yeah removing the taper pins is not too hard, I just rather not because sometimes it's easy, sometimes it's not. I rather just take the gas tube and swap it. I'm just unsure if the RIS II has enough clearance to allow me to do it |
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Originally Posted By THEdtw: Normal FSP with carbine handguards, totally doable. If you're looking at the RIS II upper, which I assume you are, I do not believe it would be possible without being able to move the FSP. This is my concern. The RIS II looks a lot less forgiving with the amount of free space you have.  I see the roll pin and the gas tube, but I don't see a way to pull that gas tube without mangling it. |
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For everyone responding, thanks for helping. Because I would be using a RIS II upper, I am not sure I would have enough space to pull it -- has anyone done it themselves? https://imgur.com/a/W2Dh1c5 |
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Originally Posted By Glockaroni: This is my concern. The RIS II looks a lot less forgiving with the amount of free space you have. https://imgur.com/a/W2Dh1c5 I see the roll pin and the gas tube, but I don't see a way to pull that gas tube without mangling it. The RIS II FSB requires the R&R of the front sight A frame and gas tube. The gas tube is pinned into the front sight, the front sight is inserted into the cutout in the top rail section, and the combined components are slid over the barrel. Do not plan to wrangle the gas tube around the front sight and out of the railed handguard without dicking it up. |
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Originally Posted By TGWLDR: The RIS II FSB requires the R&R of the front sight A frame and gas tube. The gas tube is pinned into the front sight, the front sight is inserted into the cutout in the top rail section, and the combined components are slid over the barrel. Do not plan to wrangle the gas tube around the front sight and out of the railed handguard without dicking it up. I agree, which is why I don't think it'll be viable... Do you think there's any feasibility of being able to pull it out through the upper receiver? It sucks to have to unpin that FSB, those taper pins are a pain in the ass to remove |
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Damn, been concentrating on the fire here and missed this. I would look into getting an adjustable gas key (cheap and easy) or possibly adjustable bcg (if you've got some money to burn) if you really don't want to remove the fsb. Gas key (you can also buy a bcg with it already installed) https://rubbercityarmory.com/product/rca-adjustable-gas-key/ Adjustable bcg https://www.opticsplanet.com/bootleg-inc-four-position-adjustable-carrier.html |
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Originally Posted By Cestratton85: Just remove the rail, it's only 6 screws. Am I missing something here? It's easy, but not that easy for the FSB/FSP upper. 2 screws for the bottom rail 6 screws for the handguard 2 taper pins (hammering from bolt release side towards ejection port) <-- biggest pain in the ass Slide FSB and handguard together off barrel Remove FSB Gas Tube roll pin, switch it Align FSP with handguard and barrel Tighten all The biggest pain in the butt is the FSB taper pins. Even when you hit when in the right direction, it could be a pain in the ass. |
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Originally Posted By HobbitHunter: Damn, been concentrating on the fire here and missed this. I would look into getting an adjustable gas key (cheap and easy) or possibly adjustable bcg (if you've got some money to burn) if you really don't want to remove the fsb. Gas key (you can also buy a bcg with it already installed) https://rubbercityarmory.com/product/rca-adjustable-gas-key/ Adjustable bcg https://www.opticsplanet.com/bootleg-inc-four-position-adjustable-carrier.html Yeah, I'd test first to see if the gas is that bad. On 10.3 and 11.5, it was pretty bad before changing the tube. https://www.brownells.com/gun-parts/rifle-parts/rifle-receivers-parts/m4a1-fsp-5.56x45mm-stripped-upper-receiver/?sku=430106319 Carbine gas 14.5 barrel |
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Originally Posted By Glockaroni: Yeah, I'd test first to see if the gas is that bad. On 10.3 and 11.5, it was pretty bad before changing the tube. https://www.brownells.com/gun-parts/rifle-parts/rifle-receivers-parts/m4a1-fsp-5.56x45mm-stripped-upper-receiver/?sku=430106319 Carbine gas 14.5 barrel Dude... you haven't shot it yet? 
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Originally Posted By Glockaroni: It's easy, but not that easy for the FSB/FSP upper. 2 screws for the bottom rail 6 screws for the handguard 2 taper pins (hammering from bolt release side towards ejection port) <-- biggest pain in the ass Slide FSB and handguard together off barrel Remove FSB Gas Tube roll pin, switch it Align FSP with handguard and barrel Tighten all The biggest pain in the butt is the FSB taper pins. Even when you hit when in the right direction, it could be a pain in the ass. I feel retarded now, I installed my Mk18 rail but not my FSP and now I remember why. 
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Originally Posted By HobbitHunter: Dude... you haven't shot it yet? The first 10 words of my first post are me explaining that I’m debating buying the upper lol I have a 10.3 MK18 and a 11.5 RIS III with thousands of rounds of use. This would be a new build I am planning. I started thinking of how I would go about changing the tube and then realized it might not be possible without removing the FSB. Wanted confirmation |
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Originally Posted By Cestratton85: I feel retarded now, I installed my Mk18 rail but not my FSP and now I remember why. https://www.ar15.com/media/mediaFiles/598826/20260824_204512-3816704.jpg Those are some nice builds. I’ve installed RIS II and III, but it seems that the FSP upper is annoying to remove |
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Originally Posted By Glockaroni: The first 10 words of my first post are me explaining that I’m debating buying the upper lol I have a 10.3 MK18 and a 11.5 RIS III with thousands of rounds of use. This would be a new build I am planning. I started thinking of how I would go about changing the tube and then realized it might not be possible without removing the FSB. Wanted confirmation Ah, when i saw the pics i thought this went from "thinking of buying" to 'have already bought' as typically happens. My apologies. |
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Originally Posted By gftiv: Anyone ever just try squeezing (crimping) the gas tube to restrict gas flow? You are planning to replace the tube anyway, Failure points of gas tubes are the bends. Change in direction or pinch points get hotter faster and fail sooner. Compromising the structure and adding a pinch point would give your tube a wonderful failure point. |
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OP, I grabbed a stripped upper, put a gas tube in there, and spun it with different portions of the tube in the hole in the upper. The front of the tube goes well beyond where a rail would be sitting, due to the bends in the tube near the rear portion. You could absolutely force it out and pound one back in, but my guess is you'd have a bent tube at that point that would require you to shove something in there to pry it back into place to get it to align with the hole in the FSB. Long short, either pull the thing apart or leave it be. You may be able to make it work, but it would likely be equally as annoying as taking it apart. |
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Originally Posted By Marksman14: OP, I grabbed a stripped upper, put a gas tube in there, and spun it with different portions of the tube in the hole in the upper. The front of the tube goes well beyond where a rail would be sitting, due to the bends in the tube near the rear portion. You could absolutely force it out and pound one back in, but my guess is you'd have a bent tube at that point that would require you to shove something in there to pry it back into place to get it to align with the hole in the FSB. Long short, either pull the thing apart or leave it be. You may be able to make it work, but it would likely be equally as annoying as taking it apart. Thanks for your input... I think at this point it isn't worth it. I either leave it stock and use bootleg BCG or just build out my 14.5 SOCOM RIS II upper, it'll be much easier to swap it out on that. |
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Originally Posted By gftiv: Anyone ever just try squeezing (crimping) the gas tube to restrict gas flow? You are planning to replace the tube anyway, There used to be an adjustable gas tube on the market that had a small set screw on a clamp on the tube. Haven’t seen them in a long time. |
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Originally Posted By Glockaroni: The first 10 words of my first post are me explaining that I’m debating buying the upper lol I have a 10.3 MK18 and a 11.5 RIS III with thousands of rounds of use. This would be a new build I am planning. I started thinking of how I would go about changing the tube and then realized it might not be possible without removing the FSB. Wanted confirmation I’m curious how those tubes hold up after thousands of rounds. The images from the company show erosion around the restricted tube. Seems like the thinner metal of the tube would erode pretty quick where the reduction is. |
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Originally Posted By NachoDip: I’m curious how those tubes hold up after thousands of rounds. The images from the company show erosion around the restricted tube. Seems like the thinner metal of the tube would erode pretty quick where the reduction is. 10k rds life expectancy per BRT. I have no idea how accurate that may /may not be? There's a good sized thread on TOS with quite a bit of input from users and also Clint from BRT. I did see this, and after 4 cases of ammo I thought it was in decent shape still. 
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