2aHawaii
General Topics => General Discussion => Topic started by: drck1000 on April 12, 2017, 08:02:09 AM
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What's your preference in gas length for ARs?
This came up as one of the "that's a topic for another thread" recently. Also getting back to discussion about guns.
I've had this discussion on other boards, but I figured it would be good to have it here since it came up.
My first AR was a midlength and the two ARs that I shoot most often are midlengths. I do have carbine gas ARs, but they don't get shot as much. One is waiting on a handguard, but once that is complete, it will probably get used more than the midlength guns that I have. The two midlength gas guns get shot more mostly because that's what I started with and have taken to many classes. Not really for any performance or other considerations.
Regarding performance, I have noticed that the midlength guns can be a bit less tolerant of low powered ammo. Cheap stuff like Tulammo and to a certain extent stuff like PMC Bronze. I actually really like PMC Bronze in general, but for a while with my BCM upper, I was getting occasional malfunctions that were similar to when I shot Tula. Shooting 193, 855 or even the "better" Federal .223 Rem and it was fine. Just problems with Tula and somewhat lesser problems with PMC. I was in the process of playing with buffer weights and stuff when the BCM started doing better with the PMC. Gunsmith/nut friend suspected the gas port had just eroded/loosened up enough. That happened at I think around 3,000 rounds. That's why I bought a known overgassed carbine length AR upper a couple of years ago to test with cheap ammo. Since getting the upper, I haven't been able to find Tula, or at least for cheap.
I've actually always been interested in owning a rifle length gas AR as well. It would be an M16-esque gun with iron sights only.
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My understanding (with caveat) is that the pistol length is beneficial for subsonic 300BLK with suppressor but since those are illegal in Hawaii, what's the use? For a supersonic round, is there much difference in performance between a pistol length and carbine length in terms of accuracy and functionality?
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It depends on the gas port hole drilled into the barrel.
A larger gas port may require; a longer gas travel to allow the bolt to cycle without a jam.
A smaller gas port may require ; a longer gas travel to delay the bolt from cycling to fast.
The length of the tube has to do with the cycle rate you are trying to achieve under full auto. 800rd/min 900rd/min.
under semi it doesn't really matter.
If you are just using different ammo, you may just get an adjustable gas block.
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My understanding (with caveat) is that the pistol length is beneficial for subsonic 300BLK with suppressor but since those are illegal in Hawaii, what's the use? For a supersonic round, is there much difference in performance between a pistol length and carbine length in terms of accuracy and functionality?
was that on your FAL?
Sent from my iPhone using Tapatalk
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Don't have a FAL. I do have a cheap 300BLK. I believe it's pistol length because it's about four inches from the receiver, but I'm not sure what difference it makes since I don't have a suppressor. I can see how it could come in handy when sneaking up to feral boars and you want to take out as many as you can. Don't see much use other than that...
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I would buy what you're going to shoot. Like you stated above, when you had the mid length but shot cheap ammo, you had malfunctions. So if you're going to continue to shoot the cheap stuff, buy a carbine length. My carbine length has shoot wolf ammo with no malfunctions yet.
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My understanding (with caveat) is that the pistol length is beneficial for subsonic 300BLK with suppressor but since those are illegal in Hawaii, what's the use? For a supersonic round, is there much difference in performance between a pistol length and carbine length in terms of accuracy and functionality?
Never really considered pistol length gas. I guess I would like an SBR one day with a suppressor, but was never really interested in an AR pistol. That and factoring subsonic for stuff like 300BLK. Good points. :thumbsup:
It depends on the gas port hole drilled into the barrel.
A larger gas port may require; a longer gas travel to allow the bolt to cycle without a jam.
A smaller gas port may require ; a longer gas travel to delay the bolt from cycling to fast.
The length of the tube has to do with the cycle rate you are trying to achieve under full auto. 800rd/min 900rd/min.
under semi it doesn't really matter.
If you are just using different ammo, you may just get an adjustable gas block.
I started with three midlength gas guns. A DD, BCM and LMT. You could tell that there were definitely differences in the gas "levels", for the lack of a better term for it. The DD seemed (and reportedly in the literature provided with the gun) tuned for the higher pressure 5.56 ammo. Then the BCM was "stronger" gassed than the DD and the LMT even more than both. Assumed it was due to minor variances in the gas port, but not really something that I was overly concerned about. Just more something that I noticed between the guns.
Never really thought about gas length in the context of semi vs full auto as well. The gas length, time delay, bolt speed, etc were all that I read about and was mostly aware about. But in a practical sense, as long as my guns ran well, I didn't look into them that far.
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I would buy what you're going to shoot. Like you stated above, when you had the mid length but shot cheap ammo, you had malfunctions. So if you're going to continue to shoot the cheap stuff, buy a carbine length. My carbine length has shoot wolf ammo with no malfunctions yet.
I mostly buy and shoot decent ammo. I was really looking into Tula during when ammo availability and price went crazy in the 2012-2013 time frame. Tula was still cheap then, but now it has been hard to find and when I have found it, it was the same price as 193. I'm not going to spend $300-350/1000 for Tula!
Many people say all of your guns should (reliably) shoot all the ammo you have. I haven't really tried to tweak my BCM and LMT to get to run well on Tula as they have ran fine on decent ammo. Yeah, maybe the carbine length guns are the "answer" for me for varying ammo quality and pressure. But for now, I'm ok with saying the cheap/underpowered ammo is for use with the beater carbine length gun.
I suppose the question would come to what if you had to pare down your collection, which would I keep between the midlength and the carbine. . .
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The length of the gas system (length from the receiver to the gas port) should increase as the barrel length increases.
The reason has to do with “dwell time” – the length of time that the bullet is in the barrel after the shot is fired.
On a longer barrel, the dwell time will be longer, because the bullet has to travel a longer distance. Specifically, there is a
tiny amount of time when the bullet is traveling through the barrel and it is past the gas port, but it’s still in the barrel. During
this time, there is hot gas traveling through the gas tube into the receiver. As soon as the bullet leaves the muzzle, the gas
stops flowing.
If there is too much barrel length after the gas port, then too much gas flows into the receiver and it can causes issues with
excessive recoil and wear on the rifle.
If there is not enough barrel length after the gas port, then too little gas flows into the receiver and the rifle may not cycle or
may jam.
| System | Barrel Length | Port Distance |
| Pistol | Less than 10 inches | 4 inches |
| Carbine | 10-18 inches | 7 inches |
| Mid | 14-20 inches | 9 inches |
| Rifle | 20 plus inches | 12 inches |
https://www.at3tactical.com/blogs/news/9298047-carbine-mid-or-rifle-a-beginner-s-guide-to-ar15-gas-systems
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SNIP
You have a 6940, so carbine length. Any experience with midlengths?
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I mostly buy and shoot decent ammo. I was really looking into Tula during when ammo availability and price went crazy in the 2012-2013 time frame. Tula was still cheap then, but now it has been hard to find and when I have found it, it was the same price as 193. I'm not going to spend $300-350/1000 for Tula!
Many people say all of your guns should (reliably) shoot all the ammo you have. I haven't really tried to tweak my BCM and LMT to get to run well on Tula as they have ran fine on decent ammo. Yeah, maybe the carbine length guns are the "answer" for me for varying ammo quality and pressure. But for now, I'm ok with saying the cheap/underpowered ammo is for use with the beater carbine length gun.
I suppose the question would come to what if you had to pare down your collection, which would I keep between the midlength and the carbine. . .
I shoot my wolf ammo I bought in Vegas that cost me $0.20 a round. I clean the rifle after every shoot (100rds avg per shoot), so the steel cased coated ammo doesn't bother me.
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You have a 6940, so carbine length. Any experience with midlengths?
I have the Colt carbine and a PSA upper/lower mid-length build. I also have a PWS piston and a Noveske mid-length I have yet to shoot. I have also co-built a Spikes tactical AR with Mid Length which my daughter has.
From a shooting perspective, I see no difference in the carbine versus mid. If you look at the chart, the two overlap at 14-18 inches. My 16+" barrels are well inside that range.
Since the PSA is a project gun, I opted to use a mid length for 2 reasons:
1. I like the extra length for the handguard, for both room to adjust the hold, and
2. a longer sight radius.
I wanted to try an adjustable gas block to tune the gas system, just for experimentation purposes with ammo types. Since the handguard is mid length, I figured the longer gas system would put the gas block closer to the front end, making it easier to reach the gas block with the adjusting allen wrench.
These are issues that only have to be considered it you're playing gunsmith/hobbyist and using longer-than carbine length handguards. For practice and real-world use, either length is fine.
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I have the Colt carbine and a PSA upper/lower mid-length build. I also have a PWS piston and a Noveske mid-length I have yet to shoot. I have also co-built a Spikes tactical AR with Mid Length which my daughter has.
From a shooting perspective, I see no difference in the carbine versus mid. If you look at the chart, the two overlap at 14-18 inches. My 16+" barrels are well inside that range.
Since the PSA is a project gun, I opted to use a mid length for 2 reasons:
1. I like the extra length for the handguard, for both room to adjust the hold, and
2. a longer sight radius.
I wanted to try an adjustable gas block to tune the gas system, just for experimentation purposes with ammo types. Since the handguard is mid length, I figured the longer gas system would put the gas block closer to the front end, making it easier to reach the gas block with the adjusting allen wrench.
These are issues that only have to be considered it you're playing gunsmith/hobbyist and using longer-than carbine length handguards. For practice and real-world use, either length is fine.
My BCM midlength has a FSP, but the other two are 12" free float rails/guards.
When I was looking to buy my first AR, I bought into the stated benefits/pros of midlength gas guns. Do I notice a difference? For my shooting, not really. One difference that I noticed is when shooting some match Hornady ammo that was intended for bolts guns that were showing signs of overpressure in my midlength guns. Good thing I didn't try in my carbine gas gun.
At one time, I was considering doing a build for an AR upper with "more precision" as the idea. That idea hasn't gone anywhere, but I was thinking an 18" barrel and midlength gas. Otherwise, for what I use the guns for, yeah, either are fine. Maybe carbine has an edge if it tolerates a wider range of ammo and I had to pare things down to just one AR.
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I've shot 223/556 guns with carbine length gas, mid lengths with a vltor A5 buffer, rifle length gas, 300blk with pistol and carbine gas, and 6.8spc with rifle length gas. My favorite by far is 223/556 in rifle length, but it's probably more due to the guns themselves than the gas tube length.
The only one to ever give me trouble was 300blk with carbine length gas being unreliable in feeding and failures to eject.
Pretty much none of them have had much recoil, but the rifle lengths have usually had the least. That might be more due to weight than the gas system though.
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I have everything except the pistol length. My favorite is the intermediate lengths on my 18" SS and 16" SS barrels from Noveske. I also have a Voodoo rifle length 16.5" that runs well but I don't like the very lightweight or pencil barrel profiles. I also have several carbine and midlength set ups. I don't find a huge difference in carbine to midlength in general but I do have some mid set ups with the Vltor A5's that are a noticeable improvement over most of my carbine length set ups. I will note however that I do have some carbine length set ups that feel better than mids. It really can be dependent and I do generally built with the Vltor A5. However there is a noted difference when talking intermediate to a full rifle length.
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I have a 14.5 with a mid. Shoots very well with any ammo I tried to feed it. I also have an 18" with a rifle length, it is finicky with lower power and cheap ammo. It does function with PMC, but on that ragged edge. I use this rifle with hotter loads anyway. Both seem to have a softer impulse than any carbine length I have shot. Not an AR expert by any stretch, just my observations on what I have put together. My 18 has a Viltor A5 flatwire spring, 14.5 has a Maxim collapsible with the captured buffer.
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I've shot 223/556 guns with carbine length gas, mid lengths with a vltor A5 buffer, rifle length gas, 300blk with pistol and carbine gas, and 6.8spc with rifle length gas. My favorite by far is 223/556 in rifle length, but it's probably more due to the guns themselves than the gas tube length.
The only one to ever give me trouble was 300blk with carbine length gas being unreliable in feeding and failures to eject.
Pretty much none of them have had much recoil, but the rifle lengths have usually had the least. That might be more due to weight than the gas system though.
What FPS were you loading the 300BLK to? Sounds like issues with underpressured ammo. I don't shoot 300BLK, but I shoot with many who do. I'll ask them about combinations of gas length (I assume carbine), springs, buffer, etc.
Yeah, recoil on most AR15 calibers aren't bad at all. I haven't shot the wildcat stuff like 6.5, 6.8, etc, but I can't imagine them being too bad. 5.56/.223 is nothing really. I haven't shot a rifle length gun in a while, but I would really love to own a rifle length upper. When I was thinking about getting into service rifle matches, I was close to getting a basic (irons only) upper to shoot those competitions.
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I have everything except the pistol length. My favorite is the intermediate lengths on my 18" SS and 16" SS barrels from Noveske. I also have a Voodoo rifle length 16.5" that runs well but I don't like the very lightweight or pencil barrel profiles. I also have several carbine and midlength set ups. I don't find a huge difference in carbine to midlength in general but I do have some mid set ups with the Vltor A5's that are a noticeable improvement over most of my carbine length set ups. I will note however that I do have some carbine length set ups that feel better than mids. It really can be dependent and I do generally built with the Vltor A5. However there is a noted difference when talking intermediate to a full rifle length.
I've never tried the Vltor A5, and you and a couple others have mentioned that. May have to try one of those. I have one stripped lower waiting for an "idea" and this may be it. I was saving this lower for a precision build, but time and funding what they are, that hasn't gone anywhere.
Interesting you mentioned the lightweight/pencil barrel thing. That is one of those A vs B aspect that I debated on when getting my first AR. I have two ltwt barrel ARs, but really only shoot one, the BCM. I have a 6720, but that one is still NIB. All my other ARs are either gov profile or about that weight/thickness. What about the ltwt barrels don't you care for? I haven't seen much either way, but it's not like my ARs experience heavy use very often. While I shoot the BCM with the ltwt barrel often, I have only shot the normal wt barreled guns in classes. My ARs aren't precision guns either, so I've never tested how things change as the barrel heats up nor really thought about it when shooting at "defensive" ranges. I'm one to want to try side-by-side and have always meant to shoot my different ARs with different setups on drills with a shot timer to see if I could tell the difference. Just haven't done so.
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I have a 14.5 with a mid. Shoots very well with any ammo I tried to feed it. I also have an 18" with a rifle length, it is finicky with lower power and cheap ammo. It does function with PMC, but on that ragged edge. I use this rifle with hotter loads anyway. Both seem to have a softer impulse than any carbine length I have shot. Not an AR expert by any stretch, just my observations on what I have put together. My 18 has a Viltor A5 flatwire spring, 14.5 has a Maxim collapsible with the captured buffer.
I've heard of problems with 18" and rifle combinations and seems like your experience confirms. Yeah, PMC seems to be "ok" decent. I had read about people having problems, but I never really had a problem with the AR that I shot the PMC most with, but that was a midlength that I knew was on the higher gas end of the spectrum.
Another Vltor A5 person. Damn, I feel left out. Haha.
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Another aspect that I read about often and have buddies that talk about it is the tuning of SBRs. There seems to be sweet spots on how short a barrel you can go. I haven't read or thought about it in a while, but I thought it was 10.something". Too bad no SBRs allowed here. I've shot SBRs and don't really care for them that much. If I ever got a suppressed AR, I'd really want it with an SBR.
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What FPS were you loading the 300BLK to? Sounds like issues with underpressured ammo. I don't shoot 300BLK, but I shoot with many who do. I'll ask them about combinations of gas length (I assume carbine), springs, buffer, etc.
Yeah, recoil on most AR15 calibers aren't bad at all. I haven't shot the wildcat stuff like 6.5, 6.8, etc, but I can't imagine them being too bad. 5.56/.223 is nothing really. I haven't shot a rifle length gun in a while, but I would really love to own a rifle length upper. When I was thinking about getting into service rifle matches, I was close to getting a basic (irons only) upper to shoot those competitions.
I don't know exact feet per second but I was having problems with everything except a few brands of factory supersonics. I ended up opening the gas port to 0.125" and it helped but it still doesn't run most factory or reloaded subsonics. Maybe I need to mess with it more or find another powder but I've basically thrown in the towel for now and have been looking at getting a pistol length gas Barrell for it.
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I don't know exact feet per second but I was having problems with everything except a few brands of factory supersonics. I ended up opening the gas port to 0.125" and it helped but it still doesn't run most factory or reloaded subsonics. Maybe I need to mess with it more or find another powder but I've basically thrown in the towel for now and have been looking at getting a pistol length gas Barrell for it.
Thanks for the feedback.
I don't roll my own, so that has kept me away from the 300blk. Lots of them in competition though. I'd also look at 300blk harder if going suppressed was an option.
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Thanks for the feedback.
I don't roll my own, so that has kept me away from the 300blk. Lots of them in competition though. I'd also look at 300blk harder if going suppressed was an option.
I don't bother rolling my own subsonics. What's the point? I get better accuracy with supersonic loads, use cheaper pistol powder and lighter bullets which cost less. There is no upside that I can see to load subsonic rounds. Now, if suppressors became legal for use I would start testing subsonic loads.
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I don't bother rolling my own subsonics. What's the point? I get better accuracy with supersonic loads, use cheaper pistol powder and lighter bullets which cost less. There is no upside that I can see to load subsonic rounds. Now, if suppressors became legal for use I would start testing subsonic loads.
It is my understanding that most competition shooters are rolling subsonics. Just like the handguns loads, they are tuned just above minimum power factors or function.
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It is my understanding that most competition shooters are rolling subsonics. Just like the handguns loads, they are tuned just above minimum power factors or function.
That's my understanding, too.
Now that you said it. :rofl: :rofl: :rofl:
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I've never tried the Vltor A5, and you and a couple others have mentioned that. May have to try one of those.
On a new build the A5 is my option. If a system comes without it, not sure if many would notice the benefit that much on a swap out. Just depends on the system no two are generally the same even if they are the same parts in a build.
Interesting you mentioned the lightweight/pencil barrel thing. What about the ltwt barrels don't you care for?
For the pencil barrels, I don't care for the shift in accuracy when the barrel gets heated up. Most shooters at KKHD from a bench or when shooting up close, say in the lower combat ranges may not shoot hard enough to heat the barrels or may not have an accuracy requirement when the barrel is heated up that makes a difference in their shooting. However, for myself every barrel in this "pencil type" category that I have tried (tried most of them) when I heat them up, I cannot hold an acceptable unsupported group size at 50 yards with given time constraints.
I generally tend to use the modified Navy qual as the standard to compare by and I run the qual cold and after the barrels are very much heated up for comparisons. I may also do 100 yard groups after getting a barrel pretty darn hot. Now is this shooting condition or standard that many other people will try to adhere to? Maybe not, but I see a noted difference in performance that I personally find an unacceptable trade off for any advantages that the weight savings offer.
Granted some may say that this isn't a precision weapon or those situations are not a concern for them and that is OK as my requirements may not be the same as the needs of someone else.
There seems to be sweet spots on how short a barrel you can go. I haven't read or thought about it in a while, but I thought it was 10.something".
We have run Colt 14.5's, Colt 10.3's and LMT 10.5's that were dead nuts. Dwell and unlocking is a tricky thing and some have compensated with certain extractor spring type set ups, but not everyone gets it correct. The general consensus is anywhere from 11.5 to 12.5 and in the past and for certain manufacturers there were or are certain length in front of the gas block considerations suppressor set ups.
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On a new build the A5 is my option. If a system comes without it, not sure if many would notice the benefit that much on a swap out. Just depends on the system no two are generally the same even if they are the same parts in a build.
For the pencil barrels, I don't care for the shift in accuracy when the barrel gets heated up. Most shooters at KKHD from a bench or when shooting up close, say in the lower combat ranges may not shoot hard enough to heat the barrels or may not have an accuracy requirement when the barrel is heated up that makes a difference in their shooting. However, for myself every barrel in this "pencil type" category that I have tried (tried most of them) when I heat them up, I cannot hold an acceptable unsupported group size at 50 yards with given time constraints.
I generally tend to use the modified Navy qual as the standard to compare by and I run the qual cold and after the barrels are very much heated up for comparisons. I may also do 100 yard groups after getting a barrel pretty darn hot. Now is this shooting condition or standard that many other people will try to adhere to? Maybe not, but I see a noted difference in performance that I personally find an unacceptable trade off for any advantages that the weight savings offer.
Granted some may say that this isn't a precision weapon or those situations are not a concern for them and that is OK as my requirements may not be the same as the needs of someone else.
We have run Colt 14.5's, Colt 10.3's and LMT 10.5's that were dead nuts. Dwell and unlocking is a tricky thing and some have compensated with certain extractor spring type set ups, but not everyone gets it correct. The general consensus is anywhere from 11.5 to 12.5 and in the past and for certain manufacturers there were or are certain length in front of the gas block considerations suppressor set ups.
Interesting on the A5 system. While I'm certainly interested, I can see what you mean about noticing benefit. Probably a case where things are so subtle, that many (including me) probably won't notice the difference. Like when I first got into throwing darts. A couple of my buddies had their own darts and were telling me about how they liked this or that. Didn't really matter to me at the time. But then as I started to get better, my throw more consistent, I started noticing the differences and started to figure out what was the right fit for me. Similar to the process of finding out what works best for me with guns. While it's fun to go through that process, at least for me, it can be an expensive process as well as humbling while one is still relatively early on in that process, like me. ;D
Got it on the pencil barrels. That you can see the effects at 50 yards, to the point where it gets to unacceptable group sizes is interesting. I would have thought one wouldn't be able to notice a spread until further, like 100 yards at least and probably more. However, like you said, it depends on the individual's requirements and standards. And of course baseline capabilities, which in my case I might not be able to tell if it's the gun or me to be quite frank. :(
My second AR was the BCM with light weight barrel. That was part of my normal weight vs light weight head-to-head comparisons. Other than the overall weight of the gun, I haven't really been able to shoot the BCM side-by-side with my other ARs with normal weight barrels. I haven't looked at the weights in a while, but if I recall correctly, the weight savings is about 3-4 ounces between Gov't profile and most lightweight barrels. Yeah, for those who have to carry the gun for hours on end, I am sure that can make a difference. Hell, I can feel the effects of a heavier gun after a 2-3 day carbine class. That said, in my case, the 3-4 ounces probably isn't much. Just one of those things that I always wondered about and as I settled into my AR preferences, one aspect that I haven't gotten around to testing for myself.
What I was thinking with regard to a precision AR was something with a magnified optic, like DMR/SPR type rifle. As opposed to all of my ARs are 1x red dots. I am not trying to shoot 1 MOA groups at 100 yards all day. However, that doesn't mean that I shouldn't push myself to get better accuracy/precision with what I do have. Maybe just an excuse that I've been carrying around to not have to put in the work on that regard. It's easy to punch holes in paper at 15-20 yards, but takes a lot more discipline to work on accuracy and precision. Like you said, depends on the individual's requirements and criteria on what is acceptable performance.
A bunch of the guys I shoot with and have taken classes with in AK have SBRs with suppressors. So jealous. I think mostly of them went with factory SBR uppers (DD and Colt I think) and I don't recall them having issues. Though I have read about many having issue with tuning their SBRs, but not sure if those were factory uppers or builds. I would love to have a suppressed SBR one day, but I just tell myself that I'm saving money due to them not being legal here. . . :(