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Originally Posted By Deadtired: Nonsense. The Marines got M5 RAS so they had somewhere to mount their carry handles after they were issued ACOGs.  It’s as good as any other explanation since there’s no official documentation as for what accessories to put on it. I recall at the time of the switch the mcx started carrying some of the cheaper stuff you can put on the rails. It wasn’t until years later I saw some fancier things like streamlight for personal use but I haven’t been there for years. |
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Originally Posted By chocolatechip: Here's Trey Knight speaking on what happened to the clam shell and Knight's RIS/RAS rail. Video starts at 1:15:06.  https://www.youtube.com/watch?v=hGW0WTA6xUk|4506I wonder if the RIS/ RAS pic rail farms would have still been adopted if M-lock had been a proven design in the 1990's. |
Arfcom Callsign: Meth
Never tell a bride, with dogshit on her dress, to "chillax"
Never tell a bride, with dogshit on her dress, to "chillax"
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Originally Posted By Retspag: I haven't handled any rail handguard yet that are as ergonomic as an A2 style handguard, they all feel like crap because they're round cylinders not oval and tapered like the plastic handguards. But if you need an IR laser then you need one. I never found lack of free floating to be an issue for me. Agree 100%. The A2 handguards feel great to handle, though a lot of guys prefer A1 handguards. I like them both, but I give the edge to the A2 handguards. Rails obviously feel like crap to handle, and so do the smooth M-LOK handguards in comparison to the old plastic handguards. I also think that free float isn’t that big of a deal for what the majority of ARs are going to be used for (it’s literally easy to hit at 500 meters with iron sights on a 20” A2 with good old non-free floated handguards and M855). So the biggest reason for the military switching was definitely due to wanting to mount accessories. |
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Originally Posted By Deadtired: That's very interesting regarding the double heat shield M4 clamshells. Presumably they went with that over the skinny CAR handguards for better insulation for the shooter, only to get more heat buildup under the handguard (which makes sense, insulation working both ways and all). Originally Posted By Deadtired: Originally Posted By chocolatechip: Here's Trey Knight speaking on what happened to the clam shell and Knight's RIS/RAS rail. Video starts at 1:15:06. https://www.youtube.com/watch?v=hGW0WTA6xUk|4506I just had a conversation with Google's AI about this... (lol) and we both reached the same conclusion you did, that Colt and the military primarily designed the M4 (double heat shield) handguards to increase shooter comfort by not becoming as hot as existing CAR-15 handguards, but this inadvertently caused the barrel to cool at a slightly reduced rate versus the older CAR-15 handguards. When SOCOM had the M4 handguards and the prototypes of KAC's RIS (and RAS) tested to destruction, as Trey Knight describes in the linked video, they did find that M4 barrels with the M4 handguard failed slightly sooner than those equipped with aluminum KAC quad rails, which makes perfect sense. Ultimately the military concluded a heavier barrel profile would be needed to actually solve the thermal problem, and so the M4A1 SOCOM barrel profile was adopted. It too was tested with both M4 handguards and the KAC RAS (or RIS) and they found cook-offs would happen sooner with the M4 handguards. They'd also start to warp, smoke, and ignite when continuous fire exceeds 400+ rounds. It's different when firing slowly (closer to the max sustained rate of fire) because the M4 handguards will remain cooler to the touch on the outside, while the aluminum of the KAC gets hot quicker. Google also found this 2004 thread and there are no usernames, but post #7 reads like it was authored by Trey Knight: https://www.ar15.com/forums/ar-15/-ARCHIVED-THREAD-Is-cookoff-for-real-/118-180022/?#i1386276 |
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Originally Posted By Retspag: I haven't handled any rail handguard yet that are as ergonomic as an A2 style handguard, they all feel like crap because they're round cylinders not oval and tapered like the plastic handguards. But if you need an IR laser then you need one.  https://www.ar15.com/forums/ar-15/M16A2-with-both-M68-on-Gooseneck-and-PEQ-2/127-782999/? https://wetworxoutfitters.com/surplus-m16a2-m4-an-peq2-an-paq4-barrel-mount/ |
| In the FRT era, I do value them for the insulation factor. I’ve got a weapon light mounted to the handguard, but that’s it (and all I need). I get why the military wants a better mounting structure for other devices/accessories, but they are still perfectly viable for everyday use. |
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Originally Posted By KitBuilder: That is interesting. I just had a conversation with Google's AI about this... (lol) and we both reached the same conclusion you did, that Colt and the military primarily designed the M4 (double heat shield) handguards to increase shooter comfort by not becoming as hot as existing CAR-15 handguards, but this inadvertently caused the barrel to cool at a slightly reduced rate versus the older CAR-15 handguards. When SOCOM had the M4 handguards and the prototypes of KAC's RIS (and RAS) tested to destruction, as Trey Knight describes in the linked video, they did find that M4 barrels with the M4 handguard failed slightly sooner than those equipped with aluminum KAC quad rails, which makes perfect sense. Ultimately the military concluded a heavier barrel profile would be needed to actually solve the thermal problem, and so the M4A1 SOCOM barrel profile was adopted. It too was tested with both M4 handguards and the KAC RAS (or RIS) and they found cook-offs would happen sooner with the M4 handguards. They'd also start to warp, smoke, and ignite when continuous fire exceeds 400+ rounds. It's different when firing slowly (closer the max sustained rate of fire) because the M4 handguards will remain cooler to the touch on the outside, while the aluminum of the KAC gets hot quicker. Google also found this 2004 thread and there are no usernames, but post #7 reads like it was authored by Trey Knight: https://www.ar15.com/forums/ar-15/-ARCHIVED-THREAD-Is-cookoff-for-real-/118-180022/?#i1386276 Originally Posted By KitBuilder: Originally Posted By Deadtired: Originally Posted By chocolatechip: Here's Trey Knight speaking on what happened to the clam shell and Knight's RIS/RAS rail. Video starts at 1:15:06. https://www.youtube.com/watch?v=hGW0WTA6xUk|4506I just had a conversation with Google's AI about this... (lol) and we both reached the same conclusion you did, that Colt and the military primarily designed the M4 (double heat shield) handguards to increase shooter comfort by not becoming as hot as existing CAR-15 handguards, but this inadvertently caused the barrel to cool at a slightly reduced rate versus the older CAR-15 handguards. When SOCOM had the M4 handguards and the prototypes of KAC's RIS (and RAS) tested to destruction, as Trey Knight describes in the linked video, they did find that M4 barrels with the M4 handguard failed slightly sooner than those equipped with aluminum KAC quad rails, which makes perfect sense. Ultimately the military concluded a heavier barrel profile would be needed to actually solve the thermal problem, and so the M4A1 SOCOM barrel profile was adopted. It too was tested with both M4 handguards and the KAC RAS (or RIS) and they found cook-offs would happen sooner with the M4 handguards. They'd also start to warp, smoke, and ignite when continuous fire exceeds 400+ rounds. It's different when firing slowly (closer the max sustained rate of fire) because the M4 handguards will remain cooler to the touch on the outside, while the aluminum of the KAC gets hot quicker. Google also found this 2004 thread and there are no usernames, but post #7 reads like it was authored by Trey Knight: https://www.ar15.com/forums/ar-15/-ARCHIVED-THREAD-Is-cookoff-for-real-/118-180022/?#i1386276 This is what TC 3-22x9 (2016) says about cooling: 2-22. There are three methods to reduce the thermal stress on a weapon. The M4- and M16-series of weapons use all three of these methods to varying degrees to cool the chamber, bore, and barrel to facilitate continuous operation. These methods of cooling are Radiational cooling allows for the dissipation of heat into the surrounding cooler air. This is the least efficient means of cooling, but is common to most small arms weapons, including the rifle and carbine. Conduction cooling occurs when a heated object is in direct physical contact with a cooler object. Conduction cooling on a weapon usually results from high chamber operating temperatures being transferred into surrounding surfaces such as the barrel and receiver of the weapon. The transfer from the chamber to the cooler metals has the net effect of cooling the chamber. Thermal energy is then carried away by other means, such as radiant cooling, from these newly heated surfaces. Convection cooling requires the presence of a moving air current. The moving air has greater potential to carry away heat. The hand guards and ARS of the rifle and carbine are designed to facilitate air movement. The heat shield reflects heat energy away from the hand guard and back towards the barrel. The net effect is an updraft that brings the cooler air in from the bottom. This process establishes a convection cycle as heated air is continually replaced by cooler air. |
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Originally Posted By mcantu: This is what TC 3-22x9 (2016) says about cooling: The old CAR-15 handguards should accomplish convective cooling even more effectively than M4 handguards, because if you look through them you can see the barrel. If you look into an M4 handguard you'll only see more heat shield.  It also explains why the CAR-15 handguards got so hot in the shooter's hand. There's more heat leaving through the handguard. Ultimately what mattered the most was the mass/profile of the barrel. Thicker barrels can simply take more heat before failure, and that's nothing new. EDIT: Fortunately this old blog entry from 2010 was saved on archive.org and it has temperature graphs showing the results of testing single heat shield handguards, double heat shield handguards, and Magpul MOE handguards all after 28 rounds of rapid fire. Handguard Temps: Attached File Gas Block/Barrel Temps: Attached File |
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Originally Posted By KitBuilder: I don't think they're incorrect regarding convection, but I believe the overall effect with the M4 handguards is that more heat ends up trapped around the barrel (compared to CAR-15 handguards or a KAC RAS). The old CAR-15 handguards should accomplish convective cooling even more effectively than M4 handguards, because if you look through them you can see the barrel. If you look into an M4 handguard you'll only see more heat shield. https://www.modarmory.com/wp-content/uploads/2024/12/PXL_20241227_1802330082.jpg It also explains why the CAR-15 handguards got so hot in the shooter's hand. There's more heat leaving through the handguard. Ultimately what mattered the most was the mass/profile of the barrel. Thicker barrels can simply take more heat before failure, and that's nothing new. EDIT: Fortunately this old blog entry from 2010 was saved on archive.org and it has temperature graphs showing the results of testing single heat shield handguards, double heat shield handguards, and Magpul MOE handguards all after 28 rounds of rapid fire. Handguard Temps: https://www.ar15.com/media/mediaFiles/13082/heataverageMOE_jpg-3828282.JPG Gas Block/Barrel Temps: https://www.ar15.com/media/mediaFiles/13082/heatGBMOE_jpg-3828283.JPG  |
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Originally Posted By mcantu: and on the single heat shield handguards, the vent holes line up with the ones on the outside so heat can escape easier like the manual states, by pulling cooler air in from underneath to push hot air out of the top. The single heat shield design looks to get heat out of the system more effectively while the double heat shield ones do better at keeping heat from the hand 
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Originally Posted By dalle0001: It’s as good as any other explanation since there’s no official documentation as for what accessories to put on it. I recall at the time of the switch the mcx started carrying some of the cheaper stuff you can put on the rails. It wasn’t until years later I saw some fancier things like streamlight for personal use but I haven’t been there for years. There is no official documentation because the RAS was issued as a kit (with panels and VFG, not as a rail plus all the other potential goodies that could be attached). Said accessories would be handled at the unit level. The military doesnt just issue everything to everyone at once, that is a decision made higher up the totem pole, hence the reason that some units still have older gear long after newer iterations were rolled out, such as the CompM2 a decade plus after newer optics were in use elsewhere. There is no "one size fits all" where everyone gets issued the same thing, it's why we see so many variations and combinations and why people can ask "is this clone correct?" The answer is often yes, but only for certain units or groups, not to mention individual purchases... The people making the decisions purchase on an "as needed" basis, with need being subjective based on the viewpoint of the guy authorizing the purchase. I'm not .mil and someone else that knows better can detail how that all works, but in short, no, having a place to put the carry handle is not a reason to issue quad rails - though people undoubtedly did that. |
Malcolm X was right about liberals.
Well, I've not been on much in long time or often. But I guess I fit the description from GM HYDROMATIC XM16 / M16a1's to M4 on A.D. up to the M4a1. Damn I'm old.  FYI I'm a newer "old guy" here also as my original login and name got dropped likely during my last deployment to Iraq in 08. |
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Originally Posted By KitBuilder: https://media2.giphy.com/media/CCnGOgUZPKnXSmCrnS/200.webp?cid=8dc8958camq3redpt9y02azn1wp6ir3p583humg3fg9a2109&ep=v1_gifs_search&rid=200.webp&ct=g https://www.ar15.com/forums/ar-15/M16A2-with-both-M68-on-Gooseneck-and-PEQ-2/127-782999/? https://wetworxoutfitters.com/surplus-m16a2-m4-an-peq2-an-paq4-barrel-mount/ Thanks for the post! That barrel mount looks really useful. |
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Originally Posted By Retspag: Thanks for the post! That barrel mount looks really useful. I've got one, and it worked fine on my M16A3 clone with a PEQ-2A although it really makes your sight picture "busy" just below the front blade. The NSN is 5340-01-390-3812 and Part Number A3186958.  I'm not sure how well it handles intense heat versus mounting the PEQ-2 on an M5 RAS since I never got it very hot. It also cannot additionally accommodate an M203 like the M5 RAS can. It's rare to see photos of barrel clamp mounts in U.S. military use, but that's probably because line units were getting the M4 RAS and M5 RAS not long after these were fielded. This article has photos: https://www.recoilweb.com/m16a2-of-operation-iraqi-freedom-175614.html Here's what Google has to say about them: https://share.google/aimode/24iYgZuZ04QFkxgjY (Sounds like they don't handle heat from the barrel very well at all.) EDIT: Apparently the Navy and USMC did adopt a special bracket for use with the conventional plastic M203 handguard for the M16, but it's exceptionally rare. Now I want one! Maybe NSN 5855-01-446-9545 and they say there's a post here on ARFCOM regarding this, but I cannot find it. https://www.reddit.com/r/MilitaryARClones/comments/1q8p349/m203_handguard_peq2_mounting/ Attached File |
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Originally Posted By King_Mud: I like the MOE SL profile and the way the wings cover the FSB. I picked up this furniture set at a gun show because I thought it was appropriate for my cheapy PD trade-in Bushhamster. I can see why people who carry a gun for a living might need more real estate. The most I might need is a light, so these will do fine. Attached File I do have quads and MLok handguards on other guns. |
"An age of glory passed like a lightning flash. The mandate of heaven passed from you but you didn't see. Times change and power passes. It is the pity of the world."
Song dynasty poet
Song dynasty poet
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Originally Posted By Strela: I picked up this furniture set at a gun show because I thought it was appropriate for my cheapy PD trade-in Bushhamster. I can see why people who carry a gun for a living might need more real estate. The most I might need is a light, so these will do fine. https://www.ar15.com/media/mediaFiles/6163/BushTiger3_2_jpeg-3829376.JPG I do have quads and MLok handguards on other guns. Attached File |
Arfcom Callsign: Meth
Never tell a bride, with dogshit on her dress, to "chillax"
Never tell a bride, with dogshit on her dress, to "chillax"
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Originally Posted By KitBuilder: You are quite welcome sir. I've got one, and it worked fine on my M16A3 clone with a PEQ-2A although it really makes your sight picture "busy" just below the front blade. The NSN is 5340-01-390-3812 and Part Number A3186958. https://www.globalsecurity.org/military/library/policy/army/fm/3-22-9/image1592.jpg I'm not sure how well it handles intense heat versus mounting the PEQ-2 on an M5 RAS since I never got it very hot. It also cannot additionally accommodate an M203 like the M5 RAS can. It's rare to see photos of barrel clamp mounts in U.S. military use, but that's probably because line units were getting the M4 RAS and M5 RAS not long after these were fielded. This article has photos: https://www.recoilweb.com/m16a2-of-operation-iraqi-freedom-175614.html Here's what Google has to say about them: https://share.google/aimode/24iYgZuZ04QFkxgjY (Sounds like they don't handle heat from the barrel very well at all.) EDIT: Apparently the Navy and USMC did adopt a special bracket for use with the conventional plastic M203 handguard for the M16, but it's exceptionally rare. Now I want one! Maybe NSN 5855-01-446-9545 and they say there's a post here on ARFCOM regarding this, but I cannot find it. https://www.reddit.com/r/MilitaryARClones/comments/1q8p349/m203_handguard_peq2_mounting/ https://www.ar15.com/media/mediaFiles/13082/M203versionClamp_USN_USMC_jpg-3828547.JPG I was AF TACP Guard 2001-2017 after a 10 year break from USMC 0311 1987-1991. My in processing to AF TACP completed 09/25/2001. My first drill was October 2001. Our unit was 2 years old. We had borrowed AF M16s and M16A1s then later M16A2s. We received M4 Carbines in 2002-2003 with M4 handguards. We started to receive some RAS rails. For the M4s that didn't have the RAS yet we had the bolt on brackets that interfaced with the barrel and handguard like the ones you posted to interface with our PAQ-4. I had the bracket on my M4 but don't remember zeroing the PAQ-4 until after my M4 received the RAS. I have 1 picture of my M4 with the carbine HG and bracket. I have to find it. ETA: I deployed to Iraq in 2005 using my PAQ-4. |
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