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Posted: 7/5/2010 7:32:21 AM EST
What causes the ejection port door to open when firing?

The movement of the bolt carrier group? Or gas jetting from the side of the bolt carrier group?
Link Posted: 7/5/2010 7:35:18 AM EST
The cover has a little nub that sits in the indent in the side of the carrier.  As soon as the carrier moves (from firing or charging) it pushes the door open.
Link Posted: 7/5/2010 7:35:29 AM EST
Movement of the BCG.  If the gas were blowing it open you could have to scrub carbon residue off it.
Link Posted: 7/5/2010 7:36:22 AM EST
Originally Posted By CTbuilder1:
The cover has a little nub that sits in the indent in the side of the carrier.  As soon as the carrier moves (from firing or charging) it pushes the door open.


This.  Think about it, it also opens when you pull the CH.  There is no gas until fired.

Link Posted: 7/5/2010 7:37:55 AM EST
Originally Posted By CTbuilder1:
The cover has a little nub that sits in the indent in the side of the carrier.  As soon as the carrier moves (from firing or charging) it pushes the door open.


That's what I said. But we weren't sure what the timing is of the gas coming out of the BCG. Is it excess gas that occurs after the bolt has unlocked?

Link Posted: 7/5/2010 8:09:10 AM EST
Link Posted: 7/5/2010 8:10:13 AM EST
i may get flamed, but i think it may be the gas.  obviously the door CAN be opened via the bcg moving to the rear, but the bcg doesnt move to the rear when fired until AFTER the bolt unlocks due to the gas pushing the gas rings back.  and the gas would jet out the side after that takes place before the carrier starts to move, right???  

also, my ejection port door does get a little cruddy, just not much since it only gets gassed on the first shot, if that.  most people would manually charge the gun thus opening the door before shooting anyways.
Link Posted: 7/5/2010 8:12:55 AM EST
Originally Posted By bjesse60:


+1
Link Posted: 7/5/2010 8:15:49 AM EST
I'm thinking its opened by the carrier.

Posted Via AR15.Com Mobile
Link Posted: 7/5/2010 8:16:22 AM EST
[Last Edit: 7/5/2010 8:20:48 AM EST by woode]
Originally Posted By bjesse60:


+2

Link Posted: 7/5/2010 8:18:10 AM EST
seems like a high speed camera is the answer.
Link Posted: 7/5/2010 8:21:46 AM EST
[Last Edit: 7/5/2010 8:24:43 AM EST by spoonrobot]
Originally Posted By bjesse60:


Right back at you. Sorry some of us don't have your intimate knowledge of the platform. Since this is obviously kindergarten level AR15 information could you please answer the question I asked in my second post in this thread as well as explain the timing of vented gas and bolt unlocking?

Apparently some don't know that there is gas vented out the side of the BCG upon firing, here's a video that shows this venting fairly well. Fast forward to 0:12 since the shots take forever in slow-mo.
http://www.youtube.com/watch?v=q8oP2PtL0RE

ETA: I'm not talking about what happens when you pull back the charging handle. I'm talking about what happens when the port door is closed and the rifle is fired.
Link Posted: 7/5/2010 8:22:32 AM EST
Originally Posted By woode:
Originally Posted By bjesse60:


+2



Maybe, but can we agree that the weapon may not operate the exact same way under live fire?

ps  FLAME ON!!!
Link Posted: 7/5/2010 8:22:44 AM EST
[Last Edit: 7/5/2010 8:27:58 AM EST by acman145acp]





Originally Posted By justin_schuyler:



i may get flamed, but i think it may be the gas.  obviously the door CAN be opened via the bcg moving to the rear, but the bcg doesnt move to the rear when fired until AFTER the bolt unlocks due to the gas pushing the gas rings back.  and the gas would jet out the side after that takes place before the carrier starts to move, right???  





also, my ejection port door does get a little cruddy, just not much since it only gets gassed on the first shot, if that.  most people would manually charge the gun thus opening the door before shooting anyways.



The gas pushes the carrier back which unlocks the bolt.....

This is a good read..... http://www.ar15.com/forums/topic.html?b=2&f=130&t=165511





 
Link Posted: 7/5/2010 8:24:19 AM EST
Originally Posted By WI57:
I'm thinking its opened by the carrier.

Posted Via AR15.Com Mobile


Link Posted: 7/5/2010 8:26:18 AM EST
[Last Edit: 7/5/2010 8:31:45 AM EST by woode]
The BCG is notched for the ejection port door.  The door can be latched closed when it is in the notch (bolt fully forward), or when the bolt is completely out of the way (fully rearward).  If the BCG is in motion, the BCG is in the way of the ejection port door closing, and the spring forces/holds it open.  

Gases don't reach the door before they have effect on the BCG movement.. if they did, you would have a problem.

If you own an AR15, and have even the most basic understanding of mechanics you should be able to look at it, pull your charging handle, and have your answer.

ETA: AR15 Operation 101 Animation
Link Posted: 7/5/2010 8:27:38 AM EST
Gas doesn't come out of those little holes until the BCG has already started moving rearward. Rearward movement of the BCG is what opens the port cover.
Link Posted: 7/5/2010 8:31:47 AM EST
Like others have said, it is the bcg that opens the door.  If you wonder, close the door with the bcg locked rearward, and release the bcg - you will find the door pops open upon return of the bcg, as well.
Link Posted: 7/5/2010 8:33:16 AM EST
Carrier opens the door.
Link Posted: 7/5/2010 8:35:09 AM EST
Originally Posted By acman145acp:

Originally Posted By justin_schuyler:
i may get flamed, but i think it may be the gas.  obviously the door CAN be opened via the bcg moving to the rear, but the bcg doesnt move to the rear when fired until AFTER the bolt starts to unlock due to the gas pushing against the gas rings.  and the gas would jet out the side after that takes place before the carrier starts to move, right???  

also, my ejection port door does get a little cruddy, just not much since it only gets gassed on the first shot, if that.  most people would manually charge the gun thus opening the door before shooting anyways.

The gas pushes the carrier back which unlocks the bolt.....
This is a good read..... http://www.ar15.com/forums/topic.html?b=2&f=130&t=165511
 


sorry, poor wording.  fixed it now.
Link Posted: 7/5/2010 8:40:13 AM EST
Thanks for all the smart-ass replies. Good to see some team members doing their level best to drag the technical forums down to the GD level.

Once again, we get the carrier movement will open the door if you pull the charging handle. Here's the thing, the carrier has to move @3/4 of an inch to trip the nub on the port door but it only has to move @1/4 an inch to unlock the bolt and vent gas when firing.
Link Posted: 7/5/2010 8:49:09 AM EST
Originally Posted By woode:
The BCG is notched for the ejection port door.  The door can be latched closed when it is in the notch (bolt fully forward), or when the bolt is completely out of the way (fully rearward).  If the BCG is in motion, the BCG is in the way of the ejection port door closing, and the spring forces/holds it open.  

Gases don't reach the door before they have effect on the BCG movement.. if they did, you would have a problem.

If you own an AR15, and have even the most basic understanding of mechanics you should be able to look at it, pull your charging handle, and have your answer.

ETA: AR15 Operation 101 Animation


Holy crap you're right!!!!  Thank you black rifle zen master, for i now know that charging my weapon in fact opens the ejection port cover.  please teach me more.
Link Posted: 7/5/2010 8:49:57 AM EST
Well then.

Someone needs to rig up a test bed where the bolt carrier is either limited in movement, or is modified to not open the dust cover.
Link Posted: 7/5/2010 8:50:57 AM EST
Topic needs a poll....

Personaly, I vote that the carrier opens the cover. I never notice any residue from gas on my covers...and the carriers unlatch them so nicely....would seem a given.

But then, I ain't no expert on the AR
Link Posted: 7/5/2010 8:53:05 AM EST
[Last Edit: 7/5/2010 8:55:08 AM EST by justin_schuyler]
after thinking more about it and reading some of the non-a**hole remarks, you guys are probably right.  but some of you need to learn how to take your aggression out in a productive way.

ETA  the OP was asking a friendly little question about the AR, instead of acting like he knew all that there is to know about the AR platform when he actually doesn't, unlike some people around here.
Link Posted: 7/5/2010 8:54:57 AM EST
Originally Posted By spoonrobot:
Thanks for all the smart-ass replies. Good to see some team members doing their level best to drag the technical forums down to the GD level.

Once again, we get the carrier movement will open the door if you pull the charging handle. Here's the thing, the carrier has to move @3/4 of an inch to trip the nub on the port door but it only has to move @1/4 an inch to unlock the bolt and vent gas when firing.


Sorry for the smart ass replies.  
Maybe the best way to figure out this problem would be to remove the lump on the forward portion of the carrier, remove the ejector from the bolt, load a single round in the magazine and fire it.
This way it can be answered once and for all if its the rearward motion of the carrier camming the door open or the blast from the vent.
The ejector is gone so the empty case cannot slam into the door and open it.  If the door stays shut its the carrier that opens it.
Link Posted: 7/5/2010 8:56:41 AM EST
this is true.  the gas does not come out of the small holes until the BCG starts to move rearward.  the $64 dollar question is does the gas come out of the holes before the BCG makes contact with the ejection door.  the BCG has to move back about an inch before it mechanically opens the door.  do the gases arrive before this amount of travel?
Link Posted: 7/5/2010 9:06:40 AM EST
Originally Posted By spoonrobot:
Thanks for all the smart-ass replies. Good to see some team members doing their level best to drag the technical forums down to the GD level.

Once again, we get the carrier movement will open the door if you pull the charging handle. Here's the thing, the carrier has to move @3/4 of an inch to trip the nub on the port door but it only has to move @1/4 an inch to unlock the bolt and vent gas when firing.



The door is opened by mechanical movement, not gas.....if you look at it real close, you can see the nub on the door that is in the path of the BC, when the BC hits the nub, it pops open, this occurs from rearward or forward travel.  

And yes the smart ass replies can be annoying....I do believe we have our fair share of Einsteins here on this forum....(now that is a smart ass comment, not a smart ass reply)

77
Link Posted: 7/5/2010 9:13:27 AM EST
anybody do high speed photography?
Link Posted: 7/5/2010 9:28:06 AM EST
i know that a high speed, close up video of the ejection port door opening when fired exists.  i've seen it before but i cant find it on the interwebz for the life of me now.
Link Posted: 7/5/2010 9:37:43 AM EST
to the whole damn thread. First, you have a mildly interesting question, then indignance toward the correct answer, then rationalization about whether the wrong answer might be true. Lastly, please clarify how high-speed photography can determine  what opened a closed door from the outside. Maybe high-speed X-rays?
Link Posted: 7/5/2010 9:44:19 AM EST
Originally Posted By 1saxman:
to the whole damn thread. First, you have a mildly interesting question, then indignance toward the correct answer, then rationalization about whether the wrong answer might be true. Lastly, please clarify how high-speed photography can determine  what opened a closed door from the outside. Maybe high-speed X-rays?


if the door pops open and THEN the carrier starts to move rearward, that would be an answer.  not saying that's what it would show, but its not terribly difficult to figure that one out so put your back in your fanny pack.
Link Posted: 7/5/2010 9:47:00 AM EST
Originally Posted By 1saxman:
to the whole damn thread. First, you have a mildly interesting question, then indignance toward the correct answer, then rationalization about whether the wrong answer might be true. Lastly, please clarify how high-speed photography can determine  what opened a closed door from the outside. Maybe high-speed X-rays?


High speed aimed at the empty magwell can determine if the bolt moves enough to open the door, or if the door pops open before the bolt goes back.  I say somebody write up Mythbusters.
Link Posted: 7/5/2010 9:47:00 AM EST
[Last Edit: 7/5/2010 9:49:35 AM EST by KarlSG1]
I believe the carrier impacts the nub on the ejection port door before gas pressure can build enough force to open the door. By my crude measurement, the bolt gas rings uncover the ports in the carrier at about 1/4" of movement, and the bolt carrier makes contact with the nub on the door at about 1/2" movement. At 1/4" rearward movement, the gas could start to fill the volume between the port door and the carrier, but at this point the carrier is at near full speed and probably is able to travel the next 1/4" to contact the port door much faster than gas pressure could build enough force to open the door.

You could paint the inside of the port door with Liquid Paper and close the door after chambering a round, then fire and see if it gets blackened by gas, versus if the front side of the nub gets wiped off by the carrier.

Karl
Link Posted: 7/5/2010 9:51:56 AM EST

who has a switchblock? shut the gas off and give it a try.

shut off gas, chamber a round, close port door, un-safe and fire = answer to this question.

just a thought...







my guess is that it's the carrier that opens the door.
Link Posted: 7/5/2010 9:52:55 AM EST
I just got a flashlight and looked into the small holes while pulling the bolt back.  The gas rings clearly come into view before the bolt has a chance to mechanically open the ejection door.  This means the gas comes first.  Whether it can open a closed door remains to be seen.

Link Posted: 7/5/2010 9:59:11 AM EST
Who does the dust cover get opened on an HK416, Ruger SR556, or LMT piston rifle?
Link Posted: 7/5/2010 10:01:23 AM EST
How smart do you have to be to figure it out? The carrier has a 1" notch mill in it. The ejector door latch housing sits near the rear of the notch in the milled out clearance. Any rearward movement of the carrier of 3/4" mechanically bumps the latch housing, pushing the trapdoor open. If gas opens the trapdoor with out the carrier moving, you have some serious problems. If a gas piston bolt carrier opens the trapdoor, that should be your answer. It's totally mechinical.

I didn't detect that anyone was being a smartass as much as them trying to pointout the obvious. What I find interesting is your response.
Link Posted: 7/5/2010 10:01:59 AM EST
The gas vents from the holes before the carrier impacts the nub that opens the door, but that doesn't necessarily indicate which one does the opening.
Link Posted: 7/5/2010 10:10:22 AM EST
[Last Edit: 7/5/2010 10:10:55 AM EST by par3]
Agreed ... this means that you can't categorically rule out the gas as others have tried to state in this thread (with connotations of how smart you have to be!).
Link Posted: 7/5/2010 10:12:51 AM EST
Originally Posted By Boomslang64:
The gas vents from the holes before the carrier impacts the nub that opens the door, but that doesn't necessarily indicate which one does the opening.


I dont think the gas will not have the force required.

Link Posted: 7/5/2010 10:41:25 AM EST
Originally Posted By altopwescap:
How smart do you have to be to figure it out? The carrier has a 1" notch mill in it. The ejector door latch housing sits near the rear of the notch in the milled out clearance. Any rearward movement of the carrier of 3/4" mechanically bumps the latch housing, pushing the trapdoor open. If gas opens the trapdoor with out the carrier moving, you have some serious problems. If a gas piston bolt carrier opens the trapdoor, that should be your answer. It's totally mechinical.

I didn't detect that anyone was being a smartass as much as them trying to pointout the obvious. What I find interesting is your response.


have you ever thought that its simply so the door can be opened without having to fire the weapon since there's no way to externally open it?  

believe me, we all realize that the carrier is meant to be able to open the door.  WE GET THAT.  but that does not necessarily mean that this is what happens when the gun is fired.  if gas gets the door open first, then there you go.  with the piston example you used there is no gas and the carrier HAS to open it.
Link Posted: 7/5/2010 10:43:56 AM EST
Originally Posted By KarlSG1:
I believe the carrier impacts the nub on the ejection port door before gas pressure can build enough force to open the door. By my crude measurement, the bolt gas rings uncover the ports in the carrier at about 1/4" of movement, and the bolt carrier makes contact with the nub on the door at about 1/2" movement. At 1/4" rearward movement, the gas could start to fill the volume between the port door and the carrier, but at this point the carrier is at near full speed and probably is able to travel the next 1/4" to contact the port door much faster than gas pressure could build enough force to open the door.

You could paint the inside of the port door with Liquid Paper and close the door after chambering a round, then fire and see if it gets blackened by gas, versus if the front side of the nub gets wiped off by the carrier.Karl


best idea so far.  i wish i could get to the range today and try it.
Link Posted: 7/5/2010 10:44:41 AM EST
[Last Edit: 7/5/2010 10:45:30 AM EST by HatriXx]
I would bet a good charge of my future earnings that this is purely mechanical and nothing due to the gases. If anyone has an old dust cover this could be tested easily by simply removing the nub and detent which would not be contacted by the BCG. I seriously doubt there is enough gas to blow the door open. Gases as they expand are going to travel in the path of least resistance. With the BCG already moving backward I would imagine that the gases will simply vent into the BCG and receiver. Of course testing it like this might end up in a double feed, so you would probably want to use only one round in the magazine. haha
Link Posted: 7/5/2010 10:56:30 AM EST
Originally Posted By Postal0311:
Movement of the BCG.  If the gas were blowing it open you could have to scrub carbon residue off it.


...and it wouldn't open when you cycled it by hand!
Link Posted: 7/5/2010 11:05:18 AM EST
this video, at 13 seconds, clearly shows that the gas blasts out the ports BEFORE the carrier even begins to move rearward.  now whether or not it would open the door is still in question.

http://www.youtube.com/watch?v=l5PHkv3f-9U
Link Posted: 7/5/2010 11:34:43 AM EST
[Last Edit: 7/5/2010 11:37:45 AM EST by Boomslang64]
I did a little testing.  Stand by for results and pictures.

ETA:  Delay encountered...
Link Posted: 7/5/2010 11:34:52 AM EST
Good lord people read the OP's question and the replies before replying yourself.  We are all well aware that carrier movement will open the door, the question is whether, while actually firing, gas opens the door before the carrier does.
Link Posted: 7/5/2010 11:37:24 AM EST
"Agreed ... this means that you can't categorically rule out the gas as others have tried to state in this thread (with connotations of how smart you have to be!)."

The categorical nature of the assumption is immaterial when the trapdoor is opened by a gas piston system carrier  and during the charging of a DI system by direct mechinical contact when gas pressure is not present. Shortly after the bolt is unlocked the gas pressure from the barrel drops to near zero, from there the blow back from the chamber forces the carrier group rearward. Once the bolt is unlocked the gas pressure redirects rearward to blow the BCG back instead of being forced through the gas tube.

Actually a person doesn't need to be the least bit smart to own or shoot a fire arm. My remark was not meant to be disparaging, merely trying to point out that the AR platform is a pretty basic system. With a little mechanical aptitude and a bit of common sense the AR platform is easy to understand. I'm still learning. Now I'm trying familarize myself with the AKM platform.

Link Posted: 7/5/2010 11:52:03 AM EST
Originally Posted By spoonrobot:
Thanks for all the smart-ass replies. Good to see some team members doing their level best to drag the technical forums down to the GD level.

Once again, we get the carrier movement will open the door if you pull the charging handle. Here's the thing, the carrier has to move @3/4 of an inch to trip the nub on the port door but it only has to move @1/4 an inch to unlock the bolt and vent gas when firing.


Sounds like we're trying to determine which reaches the door first, the gas or the carrier's "ramp" that opens the door.
If the gas is venting before the "ramp" reaches the door's nub, the the gas would pop it open, but only if it has enough pressure venting to do the job before the "ramp" on the BC hits it's release point for the door.
At the velocities the action takes place, it would take a high-speed camera to make the call.
Link Posted: 7/5/2010 12:16:54 PM EST
[Last Edit: 7/5/2010 12:20:56 PM EST by Boomslang64]
Here are the results of my somewhat crude test.  All the credit goes to KarlSG1 for coming up with the method.

Initially, I tried to cycle the bolt while holding the dust cover closed to create wear in order to establish the point(s) on the nub that make contact with the carrier first.  Then I went over those points with whiteout as you can see:



Next I fired 10 rounds, closing the dust cover before each round.  Here is the result:



The carbon buildup is clearly visible, but there is no apparent abrasion on the whiteout.  To ensure that the carrier wasn't acting on the dust cover in another location, I rapidly cycled the action with the dust cover closed several times.  Here is the result:



There are clearly markings where the carrier acted on the nub.  There is also whiteout present on the carrier that was not present after the live fire test.

From this basic test, I would conclude that during live fire, the venting gas pressure acts to open the dust cover before the carrier can impact it.


ETA:  Pictures fixed.
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