Warning

 

Close

Confirm Action

Are you sure you wish to do this?

Confirm Cancel
Member Login
Site Notices
9/22/2017 12:11:25 AM
Posted: 7/19/2005 1:18:28 PM EDT
I want to get an AR soon,
with this new technology just coming out do you think its worth a look over the standard carbine?
Link Posted: 7/19/2005 1:28:48 PM EDT
I like the midlength set ups. The piston setup is a whole other ball game then the midlength (I'm sure you are aware of that) To me, the midlength is nothing more then someone wanting a in between length handguard and sight radius. It really has nothing to do to change or improve the operating system of the AR. The piston on the other hand is supposed to make them a cleaner, therefore more reliable system for running lots of rounds through it without cleaning...that is the point I got from it anyway. I have a few midys and like them, i keep thinking I need a gas piston setup, but haven't bought one yet....I believe for me anyway that the piston upper is a fix to a problem I will never have....the most I ever shoot without cleaning is maybe 500-800 rounds, but usually way less. In that case, I have never had a reliability issue due to a dirty gun.

My $0.02
Link Posted: 7/19/2005 1:32:23 PM EDT
I own a midlength, but not a piston upper. That being said, I'd pick up a midlength even though there aren't an abundance of add-ons YET. I've noticed that RockRiver, and various parts companies (M&A, Midway, etc) are beginning to pick up the slack, not to mention that the mid-length gas system seems to have a softer recoil than my carbine length rifle. Too soon to tell whether this will lead to longer lasting parts.

Folks that have purchased the piston uppers (here on ARFCOM) SEEM to like them, but parts available for the various systems are proprietary i.e. not avialable from aftermarket vendors only from producer of said "system" (at least none that I know of). The jury is still out on the aforementioned as of yet.
Link Posted: 7/19/2005 1:36:59 PM EDT
I myself like mid length gas systems but the chance of the mid gas system phasing out the carbine gas system is highly unlikely.

Pistons have a future, it's just yet to be seen how much. The main thing holding it back is price, and demand. While there's probably 20k ArfCom members ranting and raving over how bad they want a piston driven upper, your typical gun owner knows nothing about them.

Carbines with standard gas systems will be the majority for a long time to come. However, if I had the extra dough for a piston driven upper, I wouldn't hesitate to shell it out.
Link Posted: 7/19/2005 1:57:55 PM EDT
According to Armalite, who are AFAIK the originators of the mid-length gas system, the mid-length gas system solves some problems the CAR-length systems have because the port is so close to the chamber and gas pressures are so high. Mostly having to do with it cycling too fast/hard. These "problems" with the CAR-length gas system have been essentially solved with things like strong extractor springs and heavier buffers. I would not consider reliability an issue with either system.

The mid-length has other advantages though, such as longer sight radius, more room on the handguards, bayonets fit on 16" barrels, and it looks better with 16" barrels. Many people who have shot both say the mid-length shoots "softer" or "smoother" because of the cycling differences noted above.

The main disadvantage of the mid-length is that it's not as common (yet) so choices are limited. That has improved a lot in the last few years though as more people discover the mid-lengths. The CAR-length system will never be obsolete though, simply because there are way too many of them out there.

My only carbine upper is a mid-length, mostly because I like the looks and the extra room on the HGs. I'll probably never own a CAR-length upper.


Gas pistons are a whole different system. I agree with HK_DUDE that the piston, while it may be an improvement, isn't enough better to justify the higher cost.
Link Posted: 7/19/2005 6:39:56 PM EDT
I want to share.....here are my midlengths

Link Posted: 7/19/2005 7:07:58 PM EDT
A longer sight radius is a good thing... http://img137.imageshack.us/img137/6601/197979122nn.jpg
Link Posted: 7/19/2005 11:20:42 PM EDT
[Last Edit: 7/19/2005 11:27:16 PM EDT by Variablebinary]
Mid length will grow in popularity
Piston's will fill a niche but never come close to being more popular than direct gas unless a unifrom standard is introduced and adopted by the majors such as Colt, HK, FN
Link Posted: 7/20/2005 12:19:13 AM EDT
[Last Edit: 7/20/2005 12:23:16 AM EDT by chewbacca]
The piston systems out there (POF and LW) are cool, but to me they make the AR a different weapon than it is. In other words, direct gas has its supposed disadvantages (shits where it eats) but it is undeniably more accurate. The modern AR with the latest and greatest (extraction upgrades etc…), by-passes any disadvantage of the direct gas while capitalizing on the inherent accuracy of the system. Besides, it is not like the combustion residue disappears with a piston system, it is just moved into another part of the weapon; a part(s) that needs to be cleaned and a part that adds non-coaxial mass reciprocation that degrades potential accuracy.

The Midlength gas system is sweet...even better would be true Dissys; 16" with a 20" gas system.
Link Posted: 7/20/2005 12:28:06 AM EDT
Pardon the noob question
Hey Chewbacca you want to explain the basic principles of the piston and midlength systems
Link Posted: 7/20/2005 6:32:42 AM EDT
Which manufacturers are making mid-lengths right now?

The only two I know of are:

-Armalite
-RRA

Which manufacturers are making mid-length parts right now?
Link Posted: 7/20/2005 7:23:21 AM EDT

Originally Posted By 22Hertz:
Which manufacturers are making mid-lengths right now?

The only two I know of are:

-Armalite
-RRA

Which manufacturers are making mid-length parts right now?



I somewhat answered that in another thread...Complete Mid-Length Uppers? You can also add KAC to that list but from what I understand, good luck actually buying one of their uppers.

I do see the mid-length trend growing and growing. It just makes too much sense and has too many things going for it not too. I do not see the military switching over to it (over their current M4 carbines) only because they have way too many M4's\carbine parts in inventory to make it financially justifiable.

As it is now, there are a lot of choices for different barrels\rail systems etc. but as more and more mid-length barrels\parts choices become available, so will their popularity. That's my opinion anyway...



Now piston driven uppers, that's another story. Unless someone comes out with a system that becomes an "industry standard" and that system becomes reasonably inexpensive to buy and easy to convert, then I doubt they will become anything more then a novelty item. L-W's system has a lot of promise and you can bet if the military goes with it (or something like it - even if only for the SCAR rifle) then you can expect them to get a lot more popular real fast
Link Posted: 7/20/2005 3:16:24 PM EDT
[Last Edit: 7/20/2005 6:15:18 PM EDT by chewbacca]

Originally Posted By 25Chuck:
Pardon the noob question
Hey Chewbacca you want to explain the basic principles of the piston and midlength systems



The piston systems work by siphoning combustion gas from the barrel into a cylinder. Inside that cylinder is a piston that is pushed rearward by the siphoned expanding gas. The piston hits a tappet that then moves rearward and impinges the bolt carrier causing it reciprocate (cycle).

At least that is the basic idea, there are many variations on the theme.

The point/theory behind a piston system is mitigating carbon (by-product of powder combustion) and heat transfer into the action. This theoretically makes the rifle more reliable and of coarse easier/quicker to clean (action at least).

The Midlength system is nothing other than the gas block being extended two inches forward on the barrel; in other words it is the normal direct gas system just extended two inches further forward than a carbine length system.

The idea behind the Midlength system is to allow more gas to be burnt in the barrel before it is siphoned out to cycle the rifle. What that means is that the siphoned gas will exhibit lower port pressure which results in a lower bolt velocity (speed at which the bolt carrier reciprocates). That translates into less wear and tear on your rifle’s components, smoother operation, lower recoil impulse and longer time for extraction.
Link Posted: 7/20/2005 5:23:11 PM EDT

Originally Posted By HK_DUDE:
{t}he midlength is nothing more then someone wanting a in between length handguard and sight radius. It really has nothing to do to change or improve the operating system of the AR.



Before even reading the rest of the thread to see if someone else already straightened you out on this, I gotta ask -- who told you that?!
Link Posted: 7/20/2005 6:36:04 PM EDT
[Last Edit: 7/20/2005 6:38:22 PM EDT by HK_DUDE]
I have had a number of CAR, Standard and middys now and none functioned better then the others, so I personally don't see a big difference in one being more reliable then the others. The question seemed to be coming from a relative newbie and I assumed he wasn't asking to the level of the exact technical differences......so, what I have experienced in the middy is exactly that...a longer sight radius and a longer handguard area.

I wasn't looking into this as far as others were...and I didn't think the poster was either. I will excuse myself from the high end physics part of this discussion.......thank you for straightening out my ingnorant ass self.

P.S. Did you read this part?

My $0.02
Link Posted: 7/20/2005 6:38:03 PM EDT
I didn't correct you, I just asked where you heard that.
Link Posted: 7/20/2005 6:40:11 PM EDT
It came from my experience with the midlength. I am sure there are SUBTLE differences in the way the gas effects the bolt, I don't debate that at all.....for the novice (Which I include myself) I don't see a big difference. I do however agree that they seem to cycle smoother.

Sorry I blew up...I guess I am touchy this evenning.
Link Posted: 7/20/2005 6:46:12 PM EDT
The mechanical advantages of the Middy are theoretical. My carbines have been basically 100% reliable (discounting bad mags and ammo). Like someone said above, with the heavy buffers and extractor upgrades (Defender, O ring etc…) on the market today the advantages of the Middy become moot.

However like HK said, you still have more hand guard area and longer sight radius in addition to the ability to put on a bayo w/no adapters.
Link Posted: 7/20/2005 6:48:37 PM EDT

Originally Posted By HK_DUDE:
It came from my experience...



Well you're one up on me because I have no middy experience. I just read about them and look at the pictures and dream of the day I'll have the dollars.
Link Posted: 7/20/2005 6:53:27 PM EDT
[Last Edit: 7/20/2005 7:39:35 PM EDT by Ellery_Holt]
Here's a great technical write-up by Mark Westrom about issues around gas systems of different lengths, and the real benefits of the mid-length over the carbine-length.

Technical Note 48, The Effects of Barrel Design and Heat on Reliability
Link Posted: 7/20/2005 7:04:46 PM EDT
Link Posted: 7/20/2005 7:11:08 PM EDT
[Last Edit: 7/20/2005 7:13:56 PM EDT by chewbacca]
Awesome TWL, can't wait to see it. Gas port errosion is a very good point, but truthfully we are talking very high round counts. Is it an issue with the military? Yes. For the average arfcommer? Probably not.
Link Posted: 7/20/2005 7:26:50 PM EDT
[Last Edit: 7/20/2005 7:38:15 PM EDT by twl]
Link Posted: 7/20/2005 8:49:36 PM EDT
[Last Edit: 7/20/2005 8:54:53 PM EDT by chewbacca]

Originally Posted By twl:
It actually begins right away, but usually doesn't become noticeable to the average shooter until some problems with reliability begin to show themselves.

It would be much more easily noticed as a rate-of-fire increase with a full-auto gun, and the user would notice it running faster fairly easily.

It will typically start to make a difference around 500 rounds fired, and may not be noticed as a problem until maybe 2000 rounds. But, it's happening. Some people will never notice it, until they start having failures, because they may not be very tuned-in to the way the gun runs.

I can pretty much tell you that if you have a reasonable amount of rounds thru your carbine, especially if you have moved to a heavy buffer to improve reliability, then you have some port erosion happening in your barrel.

Since it happens gradually as you shoot, you don't notice it easily when shooting semi-auto.
Also, if you only shoot slow fire, and don't bump-fire or run some mags real fast alot, then it will happen slower, but it will still happen.





I am not disagreeing at all, but I am just saying that average arfcommer will probably never notice any difference, this is illustrated by HK's responses. As we all know the military has been running with the m4 for some time now, and they aren't crapping out after 2000 rounds (I know that is not what you are saying per se, but that is kind of how it sounds). I am not saying the carbine gas system is the end of the story technology wise, that would be insane and I always want our guys to have the best available, but I am saying M4s are not unreliable weapons. I think this problem is analogous to a car and its piston rings. They technically start degrading after the first two feet you drive, but that doesn't mean they are a problem. They become one after "X" hundred thousand miles.


I run a H2 buffer in addition to an Oring, but not because I was having any problems but simply because I understand that they "technically" make my rig more reliable. But since my carbine has been 100% reliable before and since the upgrades I have never noticed any difference in performance, therefore it could be inferred that the "upgrades" did nothing. That is my point; I doubt the arfcommer will ever notice a difference in performance.

But, I could be wrong.
Link Posted: 7/21/2005 7:24:33 AM EDT
Link Posted: 7/21/2005 9:29:31 AM EDT
Great posts TWL, gas port erosion was something I was aware of but hadn't realized how quickly it could start to impact a weapons performance.

Learn something everyday...
Link Posted: 7/21/2005 12:48:44 PM EDT
I'm thinking along the same line as chewbacca. When you've personally owned carbines that have performed flawlessly for over 10000 rounds you probably won't lose any sleep at night over gas port erosion.
Link Posted: 7/21/2005 1:10:34 PM EDT

Originally Posted By twl:
It actually begins right away, but usually doesn't become noticeable to the average shooter until some problems with reliability begin to show themselves.

It would be much more easily noticed as a rate-of-fire increase with a full-auto gun, and the user would notice it running faster fairly easily.

It will typically start to make a difference around 500 rounds fired, and may not be noticed as a problem until maybe 2000 rounds. But, it's happening. Some people will never notice it, until they start having failures, because they may not be very tuned-in to the way the gun runs.

I can pretty much tell you that if you have a reasonable amount of rounds thru your carbine, especially if you have moved to a heavy buffer to improve reliability, then you have some port erosion happening in your barrel.

Since it happens gradually as you shoot, you don't notice it easily when shooting semi-auto.
Also, if you only shoot slow fire, and don't bump-fire or run some mags real fast alot, then it will happen slower, but it will still happen.



Any thoughts on a 14 1/2" mid length, specifically for full auto?
Link Posted: 7/21/2005 1:33:49 PM EDT
I seem to recall reading here a while back that when the USMC was deciding whether to switch to the M4 like the Army or to the M16A4 that they ran some extended reliability tests and the failure rates with the M4 were higher than the M16. Things like the stronger extractor and heavier buffer improved the M4, and the Army seems to think its reliable enough, but it's still not as good as the 20" system.



Any thoughts on a 14 1/2" mid length, specifically for full auto?

I can't think of any reason the 1.5" less of barrel after the gas port would make any difference. At most it might require a slight adjustment to gas port size like they do on the 16" with rifle HGs. But I'd guess it wouldn't even need that.
Link Posted: 7/21/2005 7:33:46 PM EDT
Link Posted: 7/22/2005 7:57:22 AM EDT

Originally Posted By chewbacca:
The piston systems out there (POF and LW) are cool, but to me they make the AR a different weapon than it is. In other words, direct gas has its supposed disadvantages (shits where it eats) but it is undeniably more accurate. The modern AR with the latest and greatest (extraction upgrades etc…), by-passes any disadvantage of the direct gas while capitalizing on the inherent accuracy of the system. Besides, it is not like the combustion residue disappears with a piston system, it is just moved into another part of the weapon; a part(s) that needs to be cleaned and a part that adds non-coaxial mass reciprocation that degrades potential accuracy.

The Midlength gas system is sweet...even better would be true Dissys; 16" with a 20" gas system.



Totally incorrect post. LW gas system fill function over 10,000 rounds without clenaing the gas piston. Accuracy is not reduced at all. Mass does not reciprocate till bullet has left the barrel. Weight is no more than standard gas tube. All points are incorrect.
Link Posted: 7/24/2005 11:42:29 AM EDT

Originally Posted By DevL:

Totally incorrect post. LW gas system fill function over 10,000 rounds without clenaing the gas piston. Accuracy is not reduced at all. Mass does not reciprocate till bullet has left the barrel. Weight is no more than standard gas tube. All points are incorrect.



Right, you still have to clean it. The LW system is by far the best system (from what I have seen) when it comes to accuracy and weight. I still don't believe how the piston does not move backwards untill the bullet has left the barrel; the gas ports are in the conventional position.
Link Posted: 7/24/2005 12:08:02 PM EDT
Easy. Compare the velocity of the round going down the barrel, to that of the moving piston (which takes time to get going, mind you).
Link Posted: 7/24/2005 1:30:53 PM EDT
[Last Edit: 7/24/2005 1:47:24 PM EDT by twl]
Link Posted: 7/24/2005 2:55:41 PM EDT
TWL, very interesting post, and educational. I appreciate you taking the time to reason with us and to give us the technical explanation.

I would modify your explanation in one aspect: though the pressure within the gas port "chamber" is equal on all sides, it seems intuitive to me that it wouldn't affect accuracy as much as you've indicated because the front sight base is fixed and the gas piston is movable. Though the pressure in the chamber is equal, the piston, being movable, will "give" and thus take the pressure off the front sight base. Thus the pressure on the FSB wouldn't seem to "flex" the barrel as much as you've conjectured.

Without really having any scientific testing to back up my claim, my suspicion here is that any effect on accuracy is going to be very minimal. Let's just pull a figure out of the air to illustrate: Could we say the accuracy degradation is only one-sixteenth of an inch at 100 yards?

Of course, as always, why not set up a scientifically valid accuracy test, with all variables controlled, and shoot "twin" direct gas and gas piston systems head-to-head.

John
Link Posted: 7/24/2005 3:19:25 PM EDT
[Last Edit: 7/24/2005 3:28:01 PM EDT by twl]
Link Posted: 7/25/2005 4:55:28 AM EDT
Link Posted: 7/25/2005 5:30:34 AM EDT
Link Posted: 7/25/2005 6:18:11 AM EDT
LeitnerWise wrote: "Interesting theory but incorrect for obvious reasons."

Sorry, but not obvious to this dunce! Care to expound, please?

John
Link Posted: 7/25/2005 10:05:04 AM EDT
tag
Link Posted: 7/25/2005 10:10:01 AM EDT
Link Posted: 7/25/2005 3:32:04 PM EDT
tag.
Link Posted: 8/23/2005 5:00:39 PM EDT
still waiting on details.
Link Posted: 8/25/2005 2:21:33 PM EDT
First, at the risk of stealing LeitnerWise's thunder (and potentially getting it wrong), I think twl's analysis of the forces at play in the piston is spot on, but identical to those in a direct impingment system so far as affecting barrel motion via force on the FSB. The torque on the barrel is caused by the gas pressure on the FSB. The geometry of the FSB and barrel is identical in both systems, and the gas pressure is determined by the ammunition used (assumed identical) and the location and size of the gas port, also assumed to be identical. So direct impingement systems and piston systems will react identically at this point. I suspect this is what LeitnerWise considers "obvious".


Second, a potentially stupid question. Assuming the following (which I suspect are correct but do not know for sure):
(1) the bore of a gas port is not chrome lined
(2) the chrome lining of a barrel resists thermal ablation/erosion better than the base metal

Why don't we chrome line the gas port bores?
Link Posted: 8/25/2005 2:41:33 PM EDT
Link Posted: 8/25/2005 2:42:45 PM EDT

Originally Posted By Ellery_Holt:
Here's a great technical write-up by Mark Westrom about issues around gas systems of different lengths, and the real benefits of the mid-length over the carbine-length.

Technical Note 48, The Effects of Barrel Design and Heat on Reliability



WOW! Well put and fairly easy to understand. Everything you ever wanted to know about carbine vs rifle reliability issues......

Cool link.
Link Posted: 8/25/2005 3:01:30 PM EDT
[Last Edit: 8/25/2005 3:04:59 PM EDT by Geohans]
Does the distance between the gas port and the muzzle affect port erosion or reliability? Or function?

For example, if you had an 18 in AR in 5.56- would it be best served by a midlength gas system or a full rifle system?

BTW, it's nice to observe a substantive discussion which has gotten to 2 pages without any s**t flying. . . .


ETA: My question is partially answered in the Armalite link, but I'd appreciate other engineers chiming in. . .
Link Posted: 8/25/2005 3:11:01 PM EDT
I don't think the distance from port to muzzle would affect erosion. It might require adjustments to the port size to maintain reliability, but IIRC the SPR is 18" and rifle-length gas system and there are 16" with rifle-length gas tubes (not the BM Dissipator, which has a CAR-length under the HGs, but there are others that don't).

The further you get from the chamber end the port is the less it will erode.
Top Top