User Panel
Posted: 1/24/2006 1:25:23 PM EDT
[Last Edit: Dano523]
I wrote this the other night in response to another post, but I think it's good enough to have it's own post.
Randall's description of AR gas operation and how everything works in harmony. I have not written this up in a while and some day I really need to build a whole page dedicated to it. This is just off the top of my head. Much of it comes from Rick McDowel (competetion specialties) when I was first learning AR's & from Tweak along the way and my own experiences mixed in along the path to enlightenment. Ok, starting with a cartridge in the chamber, hammer back. Trigger lets the hammer fall. Hammer hits the firing pin, driving it forward. Firing pin drives the primer (and attached cartridge case) forwards in the chamber until the shoulder in the chamber stops the shoulder on the cartridge case. The case will already be seated against the shoulder due to ejector tension, but the primer can sometimes move before the anvil legs on the primer stop against the primer pocket. Headspace is the distance from the bolt face to the head of the cartridge when fully seated in the chamber. Headspace gauges account for the length of the cartridge AND for the recommended amount of headspace, but what really matters is the amount of space, or lack there-of, of space between the case head and bolt face. The firing pin continues forward to ignite the primer. Primer flash ignites powder charge, instantly creating great pressure within the cartridge case. Cartridge case expands first outward towards chamber walls (path of least resistance) where pressure holds the case in place and then the case stretches backward until the case head is stopped against the bolt face. Here is WHY long headspace makes cases fail! Bullet begins movement down the barrel, first encountering the throat. Here is why you want a throat DIAMETER closely matching the bullet. More about throat dimensions can be found here: www.ar15barrels.com/data/223-556.pdf Loose throats do not control the bullet and keep it as straight while engraving into the rifling. Now the bullet has obturated and engraved into the rifling and it's accelerating rapidly down the bore. As it passes the gas port, gas begins to flow into the gas block where it turns and heads towards the bolt carrier via the gas tube. The pressure is still high in the barrel, usually 15,00PSI+ until the bullet leaves the muzzle. Just as the bullet leaves the muzzle, gas escapes around the base of the bullet. Here is why a proper crown is important. Gas is traveling about 5x faster than the bullet when it leaves the muzzle. An even crown releases gas all the way around the bullet at one time. An un-even crown lets gas go on one side first. This can tip the bullet just slightly sideways at the moment the bullet is released into the air. This is a very important time in the bullet's flight. Now, remember, high pressure gas always follows the path of least resistance, which is now out the front of the barrel instead of into the gas system. Barrel pressure drops immediatly. During the bullet's travel down the bore between the gas port and the muzzle, we had a metered amount of gas fed to the action. This gas does the following: Upon reaching the gas key bolted to the top of the carrier, it turns down into the bolt carrier where it is given a nice place to expand. This is the area inside the bolt carrier where the bolt lives. Gas expanding here forces the bolt carrier back AND the bolt forward. Note that the bolt is also being forced BACK by the gas pressure expanding the cartridge case on the other side of the bolt. For a short moment in time, these forces are about equal. Ideally, this is while the bolt lugs are unlocking and before the extractor starts pulling on the case. The bolt carrier starts to move backwards against the inertia of the carrier's weight, the buffer's weight and the operating spring. All of these effect timing, that's why we have different weights of carriers, standard, heavy (H), H2, H3 etc. The next thing the carrier encounters are the cam surfaces against the cam pin. Of course we know that the cam pin goes through the bolt. Rearward movement of the bolt carrier causes the bolt to rotate. (pay attention here, this is the meaty part) Here is where timing comes into play. Let's make a couple assumptions here before we continue. Trust me that pressures in the case hold the case into the chamber, even though the chamber is slightly tapered. Also trust me that when you release all the pressure out the front of the barrel that the cartridge case will spring back down to size so it's no longer a tight fit in the chamber as it was with the gas pressure present. Here's where timing comes into play. We want the bullet to be out of the front of the barrel AND the pressure to have subsided enough that the case shrinks down BEFORE the bolt lugs are unlocked because when the pressure is high, the case WILL try to stay in the chamber. Now is the perfect time to point out that one sure sign of high pressures are the fact that the case extrudes into the ejector plunger hole on the bolt and the resulting pressure unlocks the bolt while pressures are still high. This extruded brass gets wiped off the end of the case head, leaving a shiney spot and the brass usually makes it's way under the extractor, later causing extraction problems we will get to in a little bit. Now back to extraction, normal/correct version: Pressure subsides, bolt unlocks, carrier momentum continues rearward, pulling the fired (and contracted) cartridge case from the chamber. As the cartridge case reaches the ejection port, the case pivots on the extractor hook from pressure of the ejector until it is sent flying free of the rifle. The bolt carrier continues backward while re-cocking the hammer until operating spring pressure or the buffer stops it. Operating spring returns the bolt carrier forward where it strips another round from the magazine up the feedramps and into the chamber. Cartridge stops in the chamber, bolt continues forward, causing the extractor to snap over the rim of the cartridge case. Bolt finally stops against the case head, but the carrier continues forward. The cam surfaces in the carrier now cause the bolt to lock into battery again. Now we are back where we started. Now for extraction, the WRONG ways. First, too much gas(most common): The bullet has not left the barrel yet, but it's past the gas port. Too much high pressure gas is rushing into the carrier, causing it to move rearward faster then desired and unlock the bolt from the extension. Pressures are still high so the cartridge case is NOT ready to be extracted yet. The carrier's momentum continues to pull backward, but the pressures in the case actually hold in in the chamber. This causes a hiccup in the carrier's momentum. Depending on the severity of the timing, several things can occur: #1 The (weak) extractor spring allows the extractor to jump over the rim of the cartridge and the bolt carrier continues rearward, grabbing the next round and causing the classic "fired case in chamber, live round behind it" FTE. The brass shavings under the extractor usually contribute to this one as well. #2 The extractor does NOT slip off the case, but keeps pulling. The extractor is strong enough to RIP the rim right off the case. Same result as above, but MORE brass shavings everywhere from ripping case rims off. #3 The extractor does NOT slip off the case, but keeps pulling. During this pulling, the bullet has JUST left the bore, pressures recede and the case shrinks down, allowing extraction. The rest of the cycle goes as normal, but you have strong pull marks on the case. Recoil will be higher than normal when the carrier is allowed to travel to the end of the buffer tube and bottom out swiftly against the end of the buffer tube. In normal operation, the buffer just kisses the end of the tube. Somewhere between here and the next section, we have proper operation. Lastly, not enough gas(less common): The bullet is out of the bore, pressure is subsided, case is extracted and on it's way to ejection. Depending on the severity of the lack of gas, the bolt carrier may not even get the case out of the chamber before the operating spring returns it forward. Adding more gas, the case just barely gets out of the ejection port, but the bolt grabs it on it's way forward, classic stovepipe. Add more gas and the cartridge clears the action, but the bolt does NOT get far enough back to strip a round from the mag. This is classic short stroking. You have a single shot action which extracts and ejects, then closes on an empty chamber after you fire it. In this condition, the bolt will also ride over an empty magazine and close on an empty chamber. Add some more gas and you will reach the point where it feeds from the magazine and ALMOST works properly, but it still closes over an empty mag. This is two things, first, poor mag springs are not pushing the follower up fast enough to catch the bolt and second, the bolt is not quite making it back far enough to catch on the magazine follower. Add just a little more gas and you are back to proper function. Now, take note, that a lack of gas in a rifle that was functioning fine before can be from several things: Gas key screws poorly staked and they loosened up, allowing some gas to escape instead of doing it's job INSIDE the bolt carrier. Gas ring gaps are aligned, gas rings missing or broken, allowing extra gas to flow past them. Gas block/front sight base is loose, allowing gas to escape before it even gets down the gas tube. Gas tube "mushroom" is severly worn, probably because it was not properly aligned with the gas key and gas is escaping there. Please note that failure to extract/eject is a symptom of EITHER too much or too little function of the action. FTE alone is not enough information to decide what to change to fix the problem. You need to look for other signs such as the excessive recoil and case rim pulling of too much gas or the short stroking of too little gas. Unfortunately, many guys who don't understand the magic above always ASSUME that they have too little gas. What do they do? They open up the gas port. Following the examples above, you can see this only makes the problem worse. Lesson to be learned: Follow the published troubleshooting procedures. They are written that way for a reason. Whew, that was longer than I expected to write. Hope it all sinks in and you can benefit from it. Edited 2-3-06 to add more about gas port pressures: We often hear about mid-length being smoother cycling or pistol being harsher cycling than the typical carbine length gas systems. Below is a plot of a 223 load. I have noted the locations of the various gas ports in blue. You can plainly see what pressures are introduced into the gas systems when the bullet JUST passes the gas port. This is the reason for the way the various gas system lengths function differently. Projectile travel at the bottom assumes that the bullet starts out about 1.5" from the breech, so add 1.5" if you want to compare velocities at different lengths. Note: the site that these photo's were linked to has been disconnected, but am searching to see if I can retrieve them. If someone did save these charts/photo's, please IM me with a link so I can get them back up. Edited 4-8-07 to add more about gas system dwell time: There has been a lot of discussion lately about dwell time and how it relates to the function of certain barrels, particularly 18" rifle-gassed, 18" mid-length and 14.5" mid-lengths. I put together a new graphic to illustrate DWELL TIME. To use this graphic, find the gas port location above the pressure trace (Orange marks) and then locate the barrel lengths below the pressure trace (Blue marks). The DWELL TIME is the time between these two marks (indicated on the X axis of the graphic as well as in the data below the graphic. Optimum dwell time is right around 0.200 ms when you use the two most common gas system/barrel length configurations of 20" rifles and 14.5" carbines. Note: the site that these photo's were linked to has been disconnected, but am searching to see if I can retrieve them. If someone did save these charts/photo's, please IM me with a link so I can get them back up. |
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Randall Rausch
www.ar15barrels.com |
Hi. I'm a noob (sorry in advance). I'm looking to buy a new 16" upper for my next build, and I have been directed to this thread after asking about reliability and gas pressures. I don't want my carbine wearing out if it's avoidable, and all of the mid-length literature I have read says the standard carbine will wear out faster. I know marketing plays a factor as in, "we have a new product - time to trash the old regime to get it to sell," so I don't know how much of that is the case here.
In light of these pressure readings in the chart on page 1 of this thread, does anyone know how the higher pressure of carbines versus mid-lengths will attribute to wear of the gas system and the moving portions of the weapon? Just how much more "smooth and longer-lived" is a 16" mid-length setup if maintained properly versus a 16" standard carbine? Should I even worry about getting a mid-length gas system if all I intend to do is shoot in a range-based semi-auto fashion for thousands upon thousands of rounds over years of use and properly maintain the weapon? Do smoothness of cycle and lower pressures only really matter if I use them for full-auto or abuse my weapon (mag dumps, bump-firing, and such stupidity)? Thank you in advance! ETA: I refer above to .223/5.56 caliber weapons. Sorry for all the questions - if any at all get anwered, I'll be happy. |
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Fear not, the US military has 1000's of carbine length M4's in use. If you have the choice, go mid-length, but don't choose mid-length just because everyone says you have to. Get what you want, take care of it properly and if it's quality kit, it will serve you just fine. Now my personal 3 gun match rifle is an 18" barrel with rifle-length gas system and a big brake on the end. You want to talk about smooth shooting... It will almost keep a penny sitting on the top of the barrel without falling off between shots. |
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Randall Rausch
www.ar15barrels.com |
Executive Director, Vast Right Wing Conspiracy
NC, USA
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One of the most informative posts I've read since joining this site.
Thanx bunches |
"God created man, but Sam Colt made them equal." - Unknown
"Pistols are pistols and rifles are rifles." - Old_Painless http://en.wikipedia.org/wiki/Maxton%2C_North_Carolina كافر |
That's what I wanted to hear. Thank you! |
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The link below is to an old training video produced by the US .MIL. It's extremely dated but the basics and the how and why are still the same. Plus it's pretty damn entertaining.
www.archive.org/details/Rifle556mmXM16E1OperationandCycleofFunctioningTF93663 |
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A big thank you to Randall Rausch for posting all of the info on the AR's gas operation! It has given me some insight on a problematic AR-15. I now know it was having a short-stroking problem, but I didn't know it was called that at the time. Some modifications were made to a "plain jane" A3: YHM handguards, flip front and rear BUISs and a 6 position collapsible stock. I had told my friend that perhaps something's wrong with the buffer spring in the stock, but now I'm not so sure. Could it simply be that my friend didn't tighten the the gas block of the flip front sight? I don't recall the front sight being loose, however...
Should the gas block be checked out, or should the fixed stock (and everything else connected to it) be reinstalled? |
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Yes, it could be as simple as the gas block not fitting right, or not being aligned to the gas port. Those YHM flip-up front sights need to be forward about 1/32" from the shoulder on the barrel. |
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Randall Rausch
www.ar15barrels.com Specializing in barrel threading, shortening, lightening and any other machine work. If you want what does not exist, I can probably make it. <img src=/images/smilies/icon_smile_wink.gif border=0 align=middle> |
Now he just has to find the time to go to the range and hope he doesn't have to pull the charging handle for each round he fires.
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The key has more than enough room in its channel to accommodate the added length of a Gas tube/ block pushed all the way against the barrel shoulder. You have to remember that the differences in room we are talking about are only about 1/32" (the thickness of a front hand guard cap).
Also, just tightening up the gas Block screws may not be enough if the gas block channel to barrel port cannel is not correctly aligned. What you may suggest to your friend is that he pull the gas block forward of the barrel gas port, make a center line on the barrel shoulder dead center of the gas port, and use this line to reinstall the block (use the center line of the gas tube in the block to mate with the penciled line). Much too often, the barrel gas port may be off index with the upper's center line, and if he just uses the upper center line alone, it could be the problem. Granted that there is a little give room of the channels matching, but if the barrels gas port is not even close to the upper's center line, he may be looking at having to reinstall the barrel to get the correct zero and a functioning rifle. |
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Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds... <---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind. |
I would like to say thanks to all the people on this thread who have helped me fix my problem. This is my first post so I didn't even have to ask, there is enough info right here for me to figure out my problem and fix it in house. That means I didn't have to send my upper back and wait how-ever-many weeks to get it back so I could shoot the flippin' thing. I just bought my first AR about a month ago, a Bushie 11.5" bbl. I read the probs with shorty's and was afraid I got one of those. There are 3 of us here who bought shorty's (another 11.5" and a 10.5") and they have had no probs. I, on the other hand, thought I bought the shortest single shot in the state. My problem was a short stroke and through this thread I learned how the gas system works and have a better understanding of the gun. I thought I would have it fixed when I learned I needed an "H" buffer. I got one and still had the same trouble. When I started really looking at my gun, after reading this thread, I noticed a "powder shadow" on the gas tube in the gas block. This was my problem. The gas tube and the gas block were not lining up correctly. Why? No roll pin. The roll pin that holds the gas tube in place had not been installed and the gas tube travelled forward and misalligned on the block. Bushmaster is a top notch company and I'm sure this one just fell through the cracks, I just got lucky and bought the one the quality assurance (QA) inspector pencilwhipped, lucky me. Anyway..... Thanks guys, I learned a lot from this site and will keep coming back.
When I get my Gemtech Halo I'll post a pic. Thanks. htVF-21 Freelancers 1989-1992 |
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Tungsten AR10 Carbine Buffers => ar15.com/forums/topic.html?b=7&f=120&t=229073
Heavy Buffers for .45ACP and 9mm Uppers => ar15.com/forums/topic.html?b=7&f=25&t=263131 |
I've been trying to figure out what all that gas was doing in my rifle's bolt and this is the best information that I've been able to find anywhere.
During my search, I've also been tearing apart my AR and trying to see how the parts interacted. I have not seen anything in this thread about the firing pin. It has a flange that protrudes substantially above the bolt and, it seems to me must catch a substantial part of the gas pressure pushing backward. This would extract the firing pin from the bolt face and I was wondering what part this plays in function? |
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Do what you can, with what you have, where you are. - Theodore Roosevelt
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The stop collar on the Firing pin is part of a safety device/ protrusion limiting-factor of the FP out of the bolt face, and never during ignition, a sealing factor.
When the bolt is cam'd/lock home, the back of the bolt protrudes out the back of the carrier, which allows the FP to max out against the back of the bolt/allows full bolt face protrusion. Now if the bolt is not locked home, then the back of the bolt is contained within the carrier, and even if the hammer does strike the FP, the FP will not achieve full protrusion out the bolt face. |
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Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds... <---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind. |
Gas tube mushroom & alignment questions:
What exactly is the mushroom? On my new sabre AR, I hear a scraping as the bolt carrier slides the last bit forward. I am thinking it's the gas tube touching one side of the key interior as the key slides over it rather than going dead center into the key. Is this a misalignment problem, or of little concern. The rifle runs fine, the scraping noise just got me wondering. Thanks! |
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Pull the bolt from the carrier, then walk the carrier into the locked postion.
As long as the end of the gas tube enters the key cleanly, and the sides of the tube is not scapping down the side of the key when the carrier face kisses the barrel extenion face, you're golden. |
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Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds... <---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind. |
Randall Rausch
www.ar15barrels.com Specializing in barrel threading, shortening, lightening and any other machine work. If you want what does not exist, I can probably make it. <img src=/images/smilies/icon_smile_wink.gif border=0 align=middle> |
Thanks!
That's what I thought (Mushroom). Now how much misalignment is tolerable? (how to quantify? how to fix?) I'll try Dano's suggestion & see how it sounds. |
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The end of the tube should enter the key cleanly. If needed, pull the hand guards and tweak the tube over the top of the barrel to get the end of the tube aligned with the carrier key.
Now if the tip of the gas tube enters the key fine, but as the carrier starts to touch the barrel extension, the key rubs the side of the tube after the mushroom end, then you will need to tweak the end of the gas tube protruding inside the upper receiver to get it straight, then go back and tweak the tube about the barrel to realign. As long as the barrel nut was correctly installed (read the tube can move around in the upper a bit, and not bound up on one side of the barrel nut spines), the key should have some movement to self correct after the initial mate with the key. |
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Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds... <---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind. |
Thanks Dano & Randall!
It definitely was the mushroom rubbing as it enters the mouth of the key. I could only work inside the receiver as I have a floated handguard & no tools to remove it. The barrel nut does allow some movement of the tube so that is good. After I carefully tried to bend the tube I got the scraping reduced a bunch, but not completely. It's just scraping the mushroom, not the side of the tube. I think I'll live with it as-is for now unless you think it's a mistake to do so. Is it correct that my risk right now is that it will wear down the mushroom over the long term? Maybe one of the local guys can bring tools to a shoot sometime & I can try to get it perfect. |
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Great Job Randall!
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The gas tube I got from Bravo doesn't have a mushroom, it's straight.
JFA |
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Something's wrong... Post a close-up picture here. |
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Randall Rausch
www.ar15barrels.com Specializing in barrel threading, shortening, lightening and any other machine work. If you want what does not exist, I can probably make it. <img src=/images/smilies/icon_smile_wink.gif border=0 align=middle> |
Soon as I get a pic I'll post it. Rifle works fine though.
JFA |
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That should have been the first clue that something was not right. |
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Randall Rausch
www.ar15barrels.com Specializing in barrel threading, shortening, lightening and any other machine work. If you want what does not exist, I can probably make it. <img src=/images/smilies/icon_smile_wink.gif border=0 align=middle> |
It works and there's isn't an excessive amount of carbon in the receiver. So you think I should change it out?
JFA |
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Damn...That was a good read, thank you Sir!
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Beer, Bush, Bullshit....That pretty much sums it up.
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+1 if you were my customer, I would advise you to get a new tube. |
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Bumping to make notice that updates have been added to the original post with more detailed information about gas system dwell time.
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Randall Rausch
www.ar15barrels.com Specializing in barrel threading, shortening, lightening and any other machine work. If you want what does not exist, I can probably make it. <img src=/images/smilies/icon_smile_wink.gif border=0 align=middle> |
good stuff. Thanks Randall.
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From Randall's original post:
Upon reaching the gas key bolted to the top of the carrier, it turns down into the bolt carrier where it is given a nice place to expand. This is the area inside the bolt carrier where the bolt lives. Gas expanding here forces the bolt carrier back AND the bolt forward. Note that the bolt is also being forced BACK by the gas pressure expanding the cartridge case on the other side of the bolt. For a short moment in time, these forces are about equal. Many people do not realize this happens, or how very important it is. This pressure equalization relieves the force on the back of the bolts locking lugs and allows for easy unlocking of the bolt, and much reduced stress and wear. This relief of force does not happen in a piston/operating rod type system. BTW, the tail of the bolt IS a piston and the chamber of the bolt carrier IS a cylinder. The direct impingment system is not nearly the problem many claim it is, and it has some distinct advantages. |
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"To my mind it is wholly irresponsible to go into the world incapable of preventing violence, injury, crime, and death. How feeble is the mindset to accept defenselessness. How unnatural. How cheap. How cowardly. How pathetic." --Ted Nugent
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sweet post Randall
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"Do you see any similarities here, sir? How long before gun control proponents realize that your .223 and my 5.56mm make the exact same sized hole? "
-richardh247 |
Yes indeed it does, like straight-line thrust. |
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Randall Rausch
www.ar15barrels.com Specializing in barrel threading, shortening, lightening and any other machine work. If you want what does not exist, I can probably make it. <img src=/images/smilies/icon_smile_wink.gif border=0 align=middle> |
and its so so freaking simple |
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You may find me one day dead in a ditch somewhere. But by God, you\'ll find me in a pile of brass- Tpr. M. Padgett
See, I'm cultured. Check me out at the MET in NYC. (Behind the black box is a wang.) - Steve-Oh |
Hey Randall,
Here's a neat little animation to go with your post: www.barnesengineering.com/AR15animation/index.htm. Justin |
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You may find me one day dead in a ditch somewhere. But by God, you\'ll find me in a pile of brass- Tpr. M. Padgett
See, I'm cultured. Check me out at the MET in NYC. (Behind the black box is a wang.) - Steve-Oh |
Very helpful it answered many of my new to the AR's operation questions. Thanks for taking your time to post it.
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remember that "not enough gas" symptoms can also be caused by TOO MUCH BUFFER.
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ARin I'm RICH BITCH! |
Absolutely! Everytime someone posts how their mid-length 14.5" gun short strokes with a 9mm buffer, I have to tell them to try a regular buffer. The response is always that "well, everyone on arfcom says to run an H2, H3 or 9mm buffer". What they don't realize is that you only can do that on 16" carbines, not on 14.5" mid-lengths... |
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Randall Rausch
www.ar15barrels.com Specializing in barrel threading, shortening, lightening and any other machine work. If you want what does not exist, I can probably make it. <img src=/images/smilies/icon_smile_wink.gif border=0 align=middle> |
oh no, they will run on 14.5's......but only after there has been significant gas port erosion... in fact, a heavier buffer is a great way to deal with "too much gas" caused by gas port erosion on an old barrel. by the by, i know that YOU know all of this stuff....just for the kiddies at home. |
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ARin I'm RICH BITCH! |
Mid-length gas ports don't erode nearly as much as carbine length gas ports. Rifle ports do it even less. |
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Randall Rausch
www.ar15barrels.com Specializing in barrel threading, shortening, lightening and any other machine work. If you want what does not exist, I can probably make it. <img src=/images/smilies/icon_smile_wink.gif border=0 align=middle> |
shit.....pardon me.....i didnt notice MIDLENGTH in your previous post. |
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ARin I'm RICH BITCH! |
hey Randall, do you have graphs like those on the first page for .308 as well?
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GOA member
NRA member |
The Barnes Engineering animated graphic is a great piece of work, and shows the AR15 action very well. However, the graphic shows the gas for the bolt operation dumping into the wrong side of the piston rings or bolt rings. This could be confusing to some because it does not agree with the text posted by Randall and others. The operating gas has to dump into the chamber between the bolt and the bolt carrier BEHIND the bolt rings, not in front of the bolt rings. (In this case "front" is toward the muzzle, "BEHIND" is toward the buffer.) |
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I'm not sure I understand that chart. So which is better--- a 16 barrel with a carbine gas system or a 14.5 barrel with a mid-length gas system?
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"Don't interfere with anything in the Constitution. That must be maintained-- for it is the only safeguard of our liberties.”
--Abraham Lincoln |
So I assume for a 16" Barrel, midlength gas system, & a wylde chamber the best buffer to use is either a straight normal carbine buffer or maybe just a normal H-buffer?
Thanks for this write up... VERY informative and helpful! |
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Great article - I use Ql, but I am racking my brain trying to back calculate the dwell time figures you came up with. I was converting the velocity from fps to inch per sec. I would divide the barrel lengh from chamber to gas port (and also to muzzle) - giving millisec, but I cannot duplicate your values.
Where am I going wrong? I am having troubles reloading for a 11.5" barrel AR. I am short stroking due to low pressure or lack of pressure in the gas tube. (I believe) Factory ammo works fine. I dupicated PMC valuies in QL by disassembly and measurement of components and determinging from an ex-pmc employee of the poweer they use. Their pressure is about 67K psi (QL data) - much higher than I care to reload to. Thanks |
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I figured it out. I could not delete my past thread.
Thanks Scott |
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this is an excellent post and absolutely tons of great info
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Hello all!
This site is amazing. I rarely need to post with so many questions already answered. God bless the search function! I am a little confused on the dwell time vs. max pressure. I am considering a 16" CMMG carbine with a rifle-length system. CMMG M10 Full Length MedCon Rifle (scroll down) After reading this topic, I am now unsure if that is a wise choice. The charts Randall was so kind to produce show: 16" barrel with rifle gas = ~18k PSI and .078 dwell time 14.5" barrel with carbine gas = ~25k PSI and .206 dwell time Can someone explain which would be worse and why? Shorter dwell time vs higher pressure? I thought I had it figured out until I started to compare gas systems and barrel lengths. If .2 is the optimum dwell time, does that negate the higher pressures the carbine would be submitted to? I know that there are other options, but these were my two main selections. Carbine and rifle gas are more commonly available, and I am set on a 16" or less barrel. Longevity and reliability are the key concerns for the rifle. Am I suffering from Acute Anal Black Rifle Disease? Thanks for any help! S/F, Lee |
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