Candid Posted October 29, 2020 Report Share Posted October 29, 2020 Are there authoritative references on the gas and bolt timing for the AR -10/ Ar-15 type actions? Is it all trial by error? I would like to better understand the timing as the expansive gas opens the bolt. Rifle length, mid length. carbine length pistol length, they all are able to work, How? Gas travels at the sonic limit , and is a function of temperature. These "details" are of interest. Quote Link to comment Share on other sites More sharing options...
Candid Posted October 30, 2020 Author Report Share Posted October 30, 2020 This is good enough http://ar15barrels.com/prod/operation.shtml Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 30, 2020 Report Share Posted October 30, 2020 21 hours ago, Candid said: Are there authoritative references on the gas and bolt timing for the AR -10/ Ar-15 type actions? Is it all trial by error? I would like to better understand the timing as the expansive gas opens the bolt. Rifle length, mid length. carbine length pistol length, they all are able to work, How? Gas travels at the sonic limit , and is a function of temperature. These "details" are of interest. To a certain degree, yes, it's trial and error, especially for the different calibers that we all love. For certain calibers, it's experience, but it can be calculated to a range, and it'll work within that range, for sure. Gas Systems and Recoil Systems are tied in together, and there's no way in the world that anyone can refute that fact. They're all able to work, because of gas port diameter in the barrel. It goes way deeper than that, per gas-tube-length, though. Your later question, in red, would have been better asked first. Then it would make more sense. Read your red question first, and my answer - then read your orange question next, then my answer... What you're talking about is a Can Of Worms that I opened up here a very long time ago. I've written about it, as best I can, in detail, here. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 30, 2020 Report Share Posted October 30, 2020 22 hours ago, Candid said: Gas travels at the sonic limit , and is a function of temperature. Pressure... Has nothing to do with temperature - it's pressure. Gas PRESSURE it what operates this platform, and it doesn't matter if it's a DI system or a piston system. Quote Link to comment Share on other sites More sharing options...
DNP Posted October 30, 2020 Report Share Posted October 30, 2020 (edited) I’m sure there is a rocket scientist somewhere, maybe even a few on this board that could break everything down to the molecular level, but you have a lot of variables to account for in order to use pure math and science. Tube length, port size, dwell time, ammo, temperature, air density, barometric pressure, humidity, and the cycle of the moon and tides are probably only a few of the first factors involved....(some sarcasm added before anyone comes off the rails over that statement). It’s going to stay locked up until that bullet passes the gas port. At that time there is X amount of pressure built up behind the bullet. The ammo, or more importantly the powder uses in that ammo will be a big factor in this. The size of the gas port determines how quickly the pressure can build in the tube. The dwell time determines how quickly that pressure HAS to build in the tube. Anything can be solved on a blackboard with lots of formulas and better than average chunk of brain between the ears, but experience combined with trial and error will get you to an answer quicker I would bet. Start working on the excel spreadsheet and let’s see where this goes. Edited October 30, 2020 by DNP Typo. I aren’t one of the rocket scientists. Quote Link to comment Share on other sites More sharing options...
Lane Posted October 30, 2020 Report Share Posted October 30, 2020 28 minutes ago, DNP said: Tube length, port size, dwell time, ammo, temperature, air density, barometric pressure, humidity, and the cycle of the moon and tides are probably only a few of the first factors involved....(some sarcasm added before anyone comes off the rails over that statement). Was personally intrigued when I read the original question... I had to google the speed of sound vs. temperature to refresh my memory. I still don't know how the gas pressure comes in to play though; I assume the speed of sound is changed by that as well? Further; since it's not just "gas", a flame front moving through the barrel also going to change things a bit. Having experimented with bags full of oxy-hydrogen, I can say it's likely that the flame velocity is different than the speed of sound to begin with. I'll keep a curious eye on this thread. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 30, 2020 Report Share Posted October 30, 2020 (edited) 8 minutes ago, Lane said: Was personally intrigued when I read the original question... I had to google the speed of sound vs. temperature Speed of sound vs. temperature doesn't have a single thing to do with how an AR operates. Gas Pressure of the charge in the round has everything to do with how the AR operates. Speed of sound doesn't matter, temp doesn't matter. I can get WAY INTO how temp (and specifically, Density Altitude) affects where your bullet goes, at long range... But that doesn't have a single thing to do with how the gun actually operates. Gas pressure is what makes this gun RUN. The RECOIL SYSTEM, that's what makes this gun CYCLE... If it doesn't RUN - you have a gas problem. If it doesn't CYCLE, you have a recoil problem. If it doesn't FEED - you have a magazine problem. It doesn't get any more simple, than that. Edited October 30, 2020 by 98Z5V Quote Link to comment Share on other sites More sharing options...
Candid Posted October 30, 2020 Author Report Share Posted October 30, 2020 A study of high speed gas guns will reveal some incredible propagation velocities obtained in the high temperature wave front. That bringing in the question of the interaction of the still and cool air that is in the gas tube and bolt action volume. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 30, 2020 Report Share Posted October 30, 2020 (edited) 4 minutes ago, Candid said: A study of high speed gas guns will reveal some incredible propagation velocities obtained in the high temperature wave front. That bringing in the question of the interaction of the still and cool air that is in the gas tube and bolt action volume. You're WAY OVERTHINKING gas guns. Stop doing research, and start shooting gas guns. Post your studies, that you've been watching and learning from. I'll wait for your posts on this... Edited October 30, 2020 by 98Z5V Quote Link to comment Share on other sites More sharing options...
Candid Posted October 30, 2020 Author Report Share Posted October 30, 2020 4 minutes ago, 98Z5V said: Speed of sound vs. temperature doesn't have a single thing to do with how an AR operates. Gas Pressure of the charge in the round has everything to do with how the AR operates. Speed of sound doesn't matter, temp doesn't matter. I can get WAY INTO how temp (and specifically, Density Altitude) affects where your bullet goes, at long range... But that doesn't have a single thing to do with how the gun actually operates. Gas pressure is what makes this gun RUN. The RECOIL SYSTEM, that's what makes this gun CYCLE... One must consider that a change of PRESSURE must follow some physical SPEED LIMIT. It doesn't just happen all at once. How much time does it take for a brass casing to relax from a 50ksi stress? How much time for a steel case? These details matter. They can be resolved through BF&I (brute force and ignorance) Understanding is it's own reward. Quote Link to comment Share on other sites More sharing options...
Candid Posted October 30, 2020 Author Report Share Posted October 30, 2020 5 minutes ago, 98Z5V said: You're WAY OVERTHINKING gas guns. Stop doing research, and start shooting gas guns. Post your studies, that you've been watching and learning from. I'll wait for your posts on this... OK, simply, how much time does it take, after the projectile passes the gas port, until the bolt "sees" sufficient pressure to start moving the BC rearward and the bolt face forward? I'll wait. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 30, 2020 Report Share Posted October 30, 2020 1 minute ago, Candid said: One must consider that a change of PRESSURE You just stated the point I made - thank you. PRESSURE. Runs this gun. RECOIL SYSTEM... cycles this gun. Thank you. The Speed Limit of all the pressure that you're all wrapped up around is constricted by the size of the tube that delivers the pressure - the gas tube. The internal diamater of the gas tube is 0.125" ID, max. Never gets any bigger. Go run the math on that one. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 30, 2020 Report Share Posted October 30, 2020 2 minutes ago, Candid said: OK, simply, how much time does it take, after the projectile passes the gas port, until the bolt "sees" sufficient pressure to start moving the BC rearward and the bolt face forward? I'll wait. You just defined "Dwell Time." Congrats. Quote Link to comment Share on other sites More sharing options...
Candid Posted October 30, 2020 Author Report Share Posted October 30, 2020 10 minutes ago, 98Z5V said: You're WAY OVERTHINKING gas guns. Stop doing research, and start shooting gas guns. Post your studies, that you've been watching and learning from. I'll wait for your posts on this... Don't get me wrong, I have read many of your posts across many of the threads in this forum. You are a practical person. There may be some gaps , but you are most sincere. Is there no room for theory on this board? I am somewhat versed in high speed gas guns. Interesting things going on in those systems. Quote Link to comment Share on other sites More sharing options...
Candid Posted October 30, 2020 Author Report Share Posted October 30, 2020 3 minutes ago, 98Z5V said: You just defined "Dwell Time." Congrats. Please give a number, show your work. Insults if you must Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 30, 2020 Report Share Posted October 30, 2020 (edited) 3 minutes ago, Candid said: Don't get me wrong, I have read many of your posts across many of the threads in this forum. You are a practical person. There may be some gaps , but you are most sincere. Is there no room for theory on this board? I am somewhat versed in high speed gas guns. Interesting things going on in those systems. Point out those gaps, then. Let it rip. Plenty of room for "theory" here - and again, let that rip. Post your info. I'm always willing to learn, and do so every single day. I'm not afraid of learning something new. Edited October 30, 2020 by 98Z5V Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 30, 2020 Report Share Posted October 30, 2020 Just now, Candid said: Please give a number, show your work. Insults if you must I've already defined it, explained it - you must have missed that. Keep looking. I've explained Dwell Time. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 30, 2020 Report Share Posted October 30, 2020 2 minutes ago, Candid said: Insults if you must I'm ALWAYS down for that - let me know when we start. Quote Link to comment Share on other sites More sharing options...
Lane Posted October 30, 2020 Report Share Posted October 30, 2020 11 minutes ago, 98Z5V said: You're WAY OVERTHINKING gas guns. I disagree. In terms of internal ballistics (before the bullet leaves the barrel); the speed of sound is the same as the flame velocity inside the barrel up to the bullet passing the gas port. (pretty sure, feel free to correct me if I'm wrong here)... This is an interesting rag chew regardless of whether any of us fully understand the physics behind the gas system in that amount of depth. I could spam this thread with a ton of research papers, but even then; we would all have to read and understand them to be on the same page. High pressure is a very interesting field of study in so many disciplines; including internal ballistics. While reading some older research I was totally SHOCKED that the author used a hydraulic system to simulate case pressure to test a strain gauge attached to the outside of his rifle chamber. He wanted to calibrate it to a known pressure value, so he used what amounts to the brake system on a car to pressurize a modified brass cartridge inside the gun... Quote Link to comment Share on other sites More sharing options...
Candid Posted October 30, 2020 Author Report Share Posted October 30, 2020 I know the term, I've considered the number, I'm looking for an authoritative description with the maths. Different people have different objectives. You may like to blow things up, I like to poke holes in paper very close together. I also like to know what makes why. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 30, 2020 Report Share Posted October 30, 2020 1 minute ago, Candid said: I know the term, I've considered the number, I'm looking for an authoritative description with the maths. Different people have different objectives. You may like to blow things up, I like to poke holes in paper very close together. I also like to know what makes why. Then put in the research, discover what you're really looking for, and post back your results. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 30, 2020 Report Share Posted October 30, 2020 3 minutes ago, Lane said: I disagree. In terms of internal ballistics (before the bullet leaves the barrel); the speed of sound is the same as the flame velocity inside the barrel up to the bullet passing the gas port. (pretty sure, feel free to correct me if I'm wrong here)... In that reference, speed of sound doesn't have anything to do with it, not in the least. Speed of sound is 330m/sec. Projectiles travel alot faster than that, once fired. "Flame front velocity" all depends on the weight of the projectile, and the powder used, as to how fast that powder reacts to it's ignition, and begins pushing that projectile out of the case... Quote Link to comment Share on other sites More sharing options...
Candid Posted October 30, 2020 Author Report Share Posted October 30, 2020 1 minute ago, Lane said: I disagree. In terms of internal ballistics (before the bullet leaves the barrel); the speed of sound is the same as the flame velocity inside the barrel up to the bullet passing the gas port. (pretty sure, feel free to correct me if I'm wrong here)... This is an interesting rag chew regardless of whether any of us fully understand the physics behind the gas system in that amount of depth. I could spam this thread with a ton of research papers, but even then; we would all have to read and understand them to be on the same page. High pressure is a very interesting field of study in so many disciplines; including internal ballistics. While reading some older research I was totally SHOCKED that the author used a hydraulic system to simulate case pressure to test a strain gauge attached to the outside of his rifle chamber. He wanted to calibrate it to a known pressure value, so he used what amounts to the brake system on a car to pressurize a modified brass cartridge inside the gun... Copper compression Units are the standard for chamber pressure measurement. That is a difficult concept to get ones head around. 😉 Internal ballistics is exactly the topic. There have been some great pieces written on the topic. but.. tedious reading for anyone not inclined. Gas actuated mechanisms have added an additional level of complexity and intrigue. The referenced piece above suggests that the gas speed is 5X the MV at the muzzle. Must be greater yet at the gas port. But.. It meets with some resistance soon enough. A wall of hot spent gasses pressing on a fixed still air volume. Hmm Interesting effects to consider. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted October 30, 2020 Report Share Posted October 30, 2020 6 minutes ago, Candid said: You may like to blow things up, I like to poke holes in paper very close together. I also like to know what makes why. Tell me why you think that about me - you formed that opinion somehow? That's not the case about me at all, and if you knew me, you're DEFINITELY know better. I like shooting long distance, more than anything else, and I do it often, and I don't do it poorly. If you're here to "ask why about why" - then you need to put in your own research to satisfy your own goals in that. We don't have any guess about your "why is why" - and only you can figure that out. Be sure to post up your results, though. Quote Link to comment Share on other sites More sharing options...
Candid Posted October 30, 2020 Author Report Share Posted October 30, 2020 5 minutes ago, 98Z5V said: Then put in the research, discover what you're really looking for, and post back your results. I asked a question about available literature. If you have no awareness of any, That's OK by me. The topic is of interest to me, any at least one other member, if it is not of interest to you, that's fine. Follow your own pleasures. Quote Link to comment Share on other sites More sharing options...
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