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Posted: 2/7/2023 2:33:03 AM EDT
[#1]
16" should be Intermediate gas (ILGS) unless shooting suppressed, then you should use RLGS.
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Posted: 2/7/2023 2:34:41 AM EDT
[#2]
I've found my mid-length uppers to be noticeably smoother than any carbine uppers I've tried. Only thing that beats them is a 20" rifle-length upper, but I think a 16" middy is the best bang for your buck in a 5.56 AR.
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Posted: 2/7/2023 2:36:52 AM EDT
[#3]
14.5 middy with an A1 stock.
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Posted: 2/7/2023 2:42:58 AM EDT
[#4]
Quote HistoryQuoted: Dwell time. Everything doesn't matter. Once the bullet passes the gas port in the barrel, it's now a cork keeping pressure building up inside the gas system. A carbine length gas system on a 16" barrel means there will be additional pressure buildup in the gas system, causing the bolt to rotate faster as it unlocks from the chamber. Faster rotation means the extractor can be "flung outwards" as it rotates and lose grip on the fired case. This is why you need rubber o-rings in addition to extractor springs. Greater pressure and volume yes. It also leads to earlier unlocking with greater residual chamber pressure pressing outwards on the cartridge case wall, increased torsion on the bolt body, higher load on the locking lugs at the time of unlocking and increased BCG velocity during extraction, ejection and feeding. |
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Posted: 2/7/2023 2:53:32 AM EDT
[#5]
Mid length offers:
- Better recoil - Bayonet mounting - More handguard space for your hand - More handguard space to get a light further out on the gun - More handguard space to rest the rifle on when shooting - Longer sight radius, kind of whatever in red dot world, but its a thing - Looks cooler |
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Posted: 2/7/2023 3:18:54 AM EDT
[#6]
Quote HistoryQuoted: this. Ergos are better, everything is better. At the heart of it: 7" of dwell time is like the Avogadro's number of Stoner's design. The AR15 was designed as a rifle length barrel and rifle length gas system to have 7" of dwell time. Carbine length gas system was designed for the 14" bbl to have... 7" of dwell time! Carbine length gas system on a 16" barrel is bullshit that is the result of dumb fuck laws and nothing to do with design (eta: this combination results in 9" of dwell time). If you're stuck with a 16" bbl, then mid length gas is the correct answer - 7" of dwell time. Umm..Mid length gas is an afterthought. Original gas was either rifle or carbine. Off the top of my head..? Mid length did not start to appear until the early 90’s. There may very well be some prototype Armalites with various gas lengths but that is all. There was no one making mid length barrels at least into the 80’s and I’m thinking mid 90’s before you even heard of them. If someone has the rough date ? My foggy brain says late last years of Armalite or possibly Colt after the Govt contract..? Correct me…as needed |
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Posted: 2/7/2023 3:36:38 AM EDT
[#7]
People overthink this way too much.
The gas port location difference amounts to literally thousandths of a second. The proper function of an AR is determined by gas volume to match the reciprocating mass. The rifle needs to unlock at a specific time and maintain a specific carrier speed. Gas port location has very little to do with this. An M4 with an H2 buffer matches the unlock timing and carrier speed of a 20”. Many midlength barrels are under gassed, but will function fine in most circumstances even so. Buy what you like, it’s not going to matter if you built it right. If you’re really concerned find out what gas port diameter it has. |
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Posted: 2/7/2023 4:07:02 AM EDT
[#8]
Quote HistoryQuoted: People overthink this way too much. The gas port location difference amounts to literally thousandths of a second. The proper function of an AR is determined by gas volume to match the reciprocating mass. The rifle needs to unlock at a specific time and maintain a specific carrier speed. Gas port location has very little to do with this. An M4 with an H2 buffer matches the unlock timing and carrier speed of a 20”. Many midlength barrels are under gassed, but will function fine in most circumstances even so. Buy what you like, it’s not going to matter if you built it right. If you’re really concerned find out what gas port diameter it has. Source for unlock timing/carrier speed with H2 on 14.5 carbine? |
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Posted: 2/7/2023 4:11:05 AM EDT
[#9]
Quote HistoryQuoted: middy 16 is the perfect combo. |
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Posted: 2/7/2023 4:12:03 AM EDT
[#10]
Mid-length vs. Carbine Gas Systems in AR-pattern Rifles
The gist is that if you have a 16” barrel you want the mid length gas system. It’s better. |
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Posted: 2/7/2023 4:29:00 AM EDT
[#11]
Quote HistoryQuoted: Mid length offers: - Better recoil - Bayonet mounting - More handguard space for your hand - More handguard space to get a light further out on the gun - More handguard space to rest the rifle on when shooting - Longer sight radius, kind of whatever in red dot world, but its a thing - Looks cooler I bought a 6920 EPR and added a H2 Super42 and SSA-E. The G spring and buffer smoothed it out pretty good. Not quite as smooth as say a 16" Super Duty, but for a spare, I like it. *obviously not my photo 
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Posted: 2/7/2023 4:43:30 AM EDT
[#12]
Quote HistoryQuoted: Source for unlock timing/carrier speed with H2 on 14.5 carbine? I can’t find the video now but a suppressor company recorded bolt velocities of the different buffer weights in an M4. The chamber pressure data was in a government document and no way I’m digging that up. But for the sake of some proof for now, the M4A1 and M16A3 have matching ~750 RPM cyclic rates versus almost a thousand for an M4 with a carbine buffer. |
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Posted: 2/7/2023 5:08:13 AM EDT
[#13]
Quote HistoryQuoted: I can’t find the video now but a suppressor company recorded bolt velocities of the different buffer weights in an M4. The chamber pressure data was in a government document and no way I’m digging that up. But for the sake of some proof for now, the M4A1 and M16A3 have matching ~750 RPM cyclic rates versus almost a thousand for an M4 with a carbine buffer. Quote HistoryQuoted: Quoted: Source for unlock timing/carrier speed with H2 on 14.5 carbine? I can’t find the video now but a suppressor company recorded bolt velocities of the different buffer weights in an M4. The chamber pressure data was in a government document and no way I’m digging that up. But for the sake of some proof for now, the M4A1 and M16A3 have matching ~750 RPM cyclic rates versus almost a thousand for an M4 with a carbine buffer. And yet the 20" rifle length system experiences a lower rate of parts failures than the 14.5 carbine H2 equipped rifle. There's more to the system than RPM. The gas length absolutely plays a role in this equation as it reduces the temps of the gasses being pushed into the carrier and reduces the port/chamber pressure. The buffer does help things, no doubt but it isn't having an impact on port pressure, gas temperature in carrier or much impact on chamber pressure. |
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Posted: 2/7/2023 6:34:53 AM EDT
[#14]
Quote HistoryQuoted: And yet the 20" rifle length system experiences a lower rate of parts failures than the 14.5 carbine H2 equipped rifle. There's more to the system than RPM. The gas length absolutely plays a role in this equation as it reduces the temps of the gasses being pushed into the carrier and reduces the port/chamber pressure. The buffer does help things, no doubt but it isn't having an impact on port pressure, gas temperature in carrier or much impact on chamber pressure. Got links to evidence of parts failures with H2 buffers? Not stirring the pot, just haven’t seen much about it. With a carbine buffer it happens. It’s not because of heat though. The rifle tries to unlock early before the brass has contracted which stresses everything out. Then on the flip side the carbine buffer was also experiencing bolt bounce on return. No AR15 bolt carrier group is going to see temperatures that will damage it. A member here tested it and it took five mag dumps to break 100 degrees on the bolt. RPM is a very good tell of operating efficiency. There is an optimal carrier speed and unlocking time that requires balance in AR’s. Many say it’s the 20”. And chamber pressure is not impacted by the gas system at all. |
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Posted: 2/7/2023 6:41:24 AM EDT
[#15]
Quote HistoryQuoted: Rifle for 14.8. Mid for 14.5. My preferences are rifle, mid, carbine in that order. Each has its own purpose. |
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Posted: 2/7/2023 6:43:56 AM EDT
[#16]
Quote HistoryQuoted: Yep. The first AR I ever built was a 16" midlength FN barrel from PSA. That thing is an amazing all around rifle. Quote HistoryQuoted: Quoted: Quoted: Recoil. Mid length is much better. This. The longer the gas system (typically) the softer shooting it will be. I have one of those and agree 100%. 
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Posted: 2/7/2023 6:55:10 AM EDT
[#17]
Quote HistoryQuoted: Recoil. Mid length is much better. Having used both back to back. Mid 16 is the way to go. |
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Posted: 2/7/2023 8:55:23 AM EDT
[#18]
Quote HistoryQuoted: Recoil. Mid length is much better. It's kind of funny when people mention recoil with the AR15. |
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Posted: 2/7/2023 8:57:12 AM EDT
[#19]
Quote HistoryQuoted: I have both. I can't tell a difference. same for me. At least not in Guns at the same price range aka PSA mid / carbine length. My 18in DD shoots noticable smoother but i have not enough experience to determine which of all the better parts are responsible for it or if it is a combination. |
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Posted: 2/7/2023 9:09:51 AM EDT
[#20]
Quote HistoryQuoted: It's kind of funny when people mention recoil with the AR15. You can't tell the difference between full power m193 loads and steel case? full power isn't a magnum bolt gun by any means, but there is a difference. Try shooting a 20" rifle gas, rifle buffer back to back with a 10.5" carbine gas, carbine buffer and tell me they feel the same. |
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Posted: 2/7/2023 9:15:03 AM EDT
[#21]
Depends on what size gas port the barrel manufacturer drills. PSA seems to drill their gas ports a little larger on their Mid-lengths.
My 14.5" BCM carbine is softer shooting than my 16" PSA mid-length. |
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Posted: 2/7/2023 9:20:54 AM EDT
[#22]
Midlength is the correct length for proper gas system performance with a 16" barrel. Carbine is the correct length for a 14" barrel, and creates harsher shock load of the bolt carrier when used on a 16" barrel, but "looks cool" to some people.
I was lucky in that for the first AR I bought as a build kit, the gun counter guy at the local PSA store actually knew his stuff, and recommended that I buy the kit that had a midlength gas system. Thanks! It made all the difference in having a great first experience with this platform. |
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Posted: 2/7/2023 9:21:00 AM EDT
[#23]
Quote HistoryQuoted: I have both. I can't tell a difference. same mid looks better to me though 
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Posted: 2/7/2023 9:30:41 AM EDT
[#24]
Quote HistoryQuoted: 16" should be Intermediate gas (ILGS) unless shooting suppressed, then you should use RLGS. Lol. I know a small fleet of 16” carbine Colts that exclusively shot suppressed from helicopters. They don’t malfunction even with brass catchers and noibs shooting them. |
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Posted: 2/7/2023 9:34:22 AM EDT
[#25]
My 6920's definitely had more perceived recoil/muzzle rise than my BCM 16" middies (both w/carbine buffers).
Adding the H2 buffer to my BCM middies was the 'sweet spot' for me. Very smooth and not a single malf after thousands of rds (and that includes a 1,000rd test w/no lube/cleaning during the thousand rds). |
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Posted: 2/7/2023 9:48:33 AM EDT
[#26]
IMHO people on this site overemphasize the importance of gas system length and make a lot of unqualified statements like "well I have a mid that shoots smoother than a carbine I also have" without any sort of mention of port size, buffer weight, etc...
There are several other considerations that are more important. |
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Posted: 2/7/2023 9:58:13 AM EDT
[#27]
Tech talk is beyond me, but the 1 middy I used to have, I saw zero difference in shooting then the pinned 14.5' carbines I use. I also thought it looked goofy. Also couldn't standardize on parts. It was sold & I have no plans to buy another.
I own 1 16" & plan on selling that upper. |
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Posted: 2/7/2023 10:09:18 AM EDT
[#28]
Quote HistoryQuoted: It's kind of funny when people mention recoil with the AR15. Tell me you don’t shoot fast without saying you don’t shoot fast. |
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Posted: 2/7/2023 10:14:55 AM EDT
[#29]
Quote HistoryQuoted: It's kind of funny when people mention recoil with the AR15. 
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Posted: 2/7/2023 10:59:30 AM EDT
[#30]
Gas port size is much more important
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Posted: 2/7/2023 11:12:12 AM EDT
[#31]
12.5" and up - Mid
Below 12.5" - Carbine |
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Posted: 2/7/2023 11:18:15 AM EDT
[#32]
Quote HistoryQuoted: Gas port size is much more important |
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Posted: 2/7/2023 11:30:40 AM EDT
[#33]
Quote HistoryQuoted: Try shooting a 20" rifle gas, rifle buffer back to back with a 10.5" carbine gas, carbine buffer and tell me they feel the same. like saying have a 10 year old girl punch you in the arm and a 11 year old girl punch you in the arm and then asking if they feel the same who cares its still just a little girl punching you in the arm |
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Posted: 2/7/2023 11:36:55 AM EDT
[#34]
Quote HistoryQuoted: In general terms, midlength uppers are more reliable. There was some pretty significant (a couple ten thousands of rounds) testing I did on a couple midlength uppers vs carbine uppers before pushing for APC to standardize on recommending midlength. Plus you can use it with a bayonet. Poke all the things! Quote HistoryQuoted: Quoted: A while back I had bought a mid length freedom upper from PSA. It was a deal of the day and was fairly cheep. I overlooked the fact that it was a mid length. I'm kind of embarrassed to admit, I couldn't tell you what the advantage is of one over the other. So school me GD. In general terms, midlength uppers are more reliable. There was some pretty significant (a couple ten thousands of rounds) testing I did on a couple midlength uppers vs carbine uppers before pushing for APC to standardize on recommending midlength. Plus you can use it with a bayonet. Poke all the things! Cold weather, low power ammo, dirty rifle, suppressed? I find gas port and good ammo has more bearing on reliability and gas length preferences |
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Posted: 2/7/2023 11:37:24 AM EDT
[#35]
Quote HistoryQuoted: 16 mid with H buffer and 16 carbine with H2 will feel almost identical imo. Rifle extension, rifle spring, H2 buffer, Mid-length gas, Turbo K 
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Posted: 2/7/2023 12:05:45 PM EDT
[#36]
Quote HistoryQuoted: Mid length offers: - Better recoil - Bayonet mounting - More handguard space for your hand - More handguard space to get a light further out on the gun - More handguard space to rest the rifle on when shooting - Longer sight radius, kind of whatever in red dot world, but its a thing - Looks cooler 13" and 15" rails work with both gas systems. A properly sized GP means all points are moot. |
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Posted: 2/7/2023 12:25:57 PM EDT
[#37]
Quote HistoryQuoted: Mid length offers: - Better recoil - Bayonet mounting - More handguard space for your hand - More handguard space to get a light further out on the gun - More handguard space to rest the rifle on when shooting - Longer sight radius, kind of whatever in red dot world, but its a thing - Looks cooler None of these have anything to do with gas length "Looks cooler" is subjective. There are carbines that shoot smoother than some mids, there are more variables at play than gas length. |
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Posted: 2/7/2023 12:29:46 PM EDT
[#38]
Quote HistoryQuoted: 13" and 15" rails work with both gas systems. A properly sized GP means all points are moot. Quote HistoryQuoted: 13" and 15" rails work with both gas systems. A properly sized GP means all points are moot. Quoted: None of these have anything to do with gas length "Looks cooler" is subjective. There are carbines that shoot smoother than some mids, there are more variables at play than gas length. I'm under the impression OP has gone with a FSB and two piece handguards. |
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Posted: 2/7/2023 12:36:08 PM EDT
[#39]
Less buffer spring twang is enough to win me over.
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Posted: 2/7/2023 12:37:36 PM EDT
[#40]
Quote HistoryQuoted: I'm under the impression OP has gone with a FSB and two piece handguards.  
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Posted: 2/7/2023 12:38:52 PM EDT
[#41]
Quote HistoryQuoted: It's kind of funny when people mention recoil with the AR15. agree but i guess there are a lot of 556 AR shooters who have never shot larger caliber firearms |
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Posted: 2/7/2023 12:46:37 PM EDT
[#42]
Quote HistoryGood buddy, I think you're being a little pedantic giving examples of $200 handguards when OP tell us how he just bought a $250 complete upper.
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Posted: 2/7/2023 12:51:38 PM EDT
[#43]
Quote HistoryQuoted: People overthink this way too much. The gas port location difference amounts to literally thousandths of a second. The proper function of an AR is determined by gas volume to match the reciprocating mass. The rifle needs to unlock at a specific time and maintain a specific carrier speed. Gas port location has very little to do with this. An M4 with an H2 buffer matches the unlock timing and carrier speed of a 20”. Many midlength barrels are under gassed, but will function fine in most circumstances even so. Buy what you like, it’s not going to matter if you built it right. If you’re really concerned find out what gas port diameter it has. I didn't have any concern, per se, it's new and different to me. Just wanted to see what some of the nuances were. Many of the posts have given me the gist of it. Thanks everybody! |
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Posted: 2/7/2023 1:09:01 PM EDT
[#44]
Quote HistoryQuoted: like saying have a 10 year old girl punch you in the arm and a 11 year old girl punch you in the arm and then asking if they feel the same who cares its still just a little girl punching you in the arm Quote HistoryQuoted: Quoted: Try shooting a 20" rifle gas, rifle buffer back to back with a 10.5" carbine gas, carbine buffer and tell me they feel the same. like saying have a 10 year old girl punch you in the arm and a 11 year old girl punch you in the arm and then asking if they feel the same who cares its still just a little girl punching you in the arm |
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Posted: 2/7/2023 1:29:37 PM EDT
[#45]
Quote HistoryQuoted: Good buddy, I think you're being a little pedantic giving examples of $200 handguards when OP tell us how he just bought a $250 complete upper. But the cost of the handguards isn't relevant at all, I posted those to demonstrate that gas length doesn't determine handguard length or most of the other things you mentioned (aside from maybe sight radius if you have a FSP). These are within $10 of each other and have the same barrel length (may even be the same barrel minus gas block journal and port location), same rail, etc... They are the same aside from the gas system length: https://palmettostatearmory.com/psa-16-m4-carbine-5-56-nato-1-7-nitride-13-5-m-lok-freedom-upper-no-bcg-or-ch-516444536.html https://palmettostatearmory.com/psa-16-mid-length-5-56-nato-1-7-nitride-13-5-lightweight-m-lok-upper-without-bcg-or-ch-516446782.html |
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Posted: 2/7/2023 1:32:13 PM EDT
[#46]
MHO: midlength has some utility on a 16" barrel. Shorter or longer? no.
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Posted: 2/7/2023 1:39:27 PM EDT
[#47]
Responses one and two said mid was more reliable and recoil was milder OP. Others have said the mid was "smoother."
I have not been able to determine that much of difference between the two systems. |
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Posted: 2/7/2023 1:44:08 PM EDT
[#48]
Quote HistoryQuote HistoryQuoted: Quoted: I'm under the impression OP has gone with a FSB and two piece handguards. https://uploads.tapatalk-cdn.com/20210206/cfcac48801e3331ab0a327aa47cfd1e3.jpg https://farm8.staticflickr.com/7307/13244267875_cd13b69a00_b.jpg So you want your FSB... |
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Posted: 2/7/2023 1:56:33 PM EDT
[#49]
Quote HistoryQuoted: So you want your FSB... I've been known to enjoy a FSB from time to time. If you like your FSB, you can keep your FSB.
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Posted: 2/7/2023 2:04:01 PM EDT
[#50]
Quote HistoryQuoted: agree but i guess there are a lot of 556 AR shooters who have never shot larger caliber firearms How fast are your A zone splits at 300 yards? |
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