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Posted: 1/5/2021 11:40:14 AM EDT
I began the process of "building my own" AR-15. I'm 90% done with my 1st build. It's been a challenge But I'm getting there. I'll explain more once I can make longer posts.
 Once I finish, I have a different problem. How to "test fire" it.... Since I live in an urban area, I can't just shoot off rounds to test fire. And I want to test cycle the action safely before going up to the country and testing with live rounds. So I thought, would there be a way to test/simulate the gas action cycle by blowing a shot of compressed air down the barrel, simulating the firing of a round and causing the action to cycle. I would use 5.56 snap caps (and, perhaps even an empty 5.56 shell as the first extraction) and, as long as it was able to cycle properly a few times, then I'd think it safe to test fire with live rounds. Is this something that's normally done? Or do you just go ahead and test with live rounds? The two issues I face with this method are:
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Posted: 1/5/2021 11:54:02 AM EDT
[#1]
First post?
You won't get enough pressure to cycle the action, but shop air pressure can get it to unlock. What you are proposing is not a normal practice. If you used quality parts and ammo it won't blow up on you. For reference, the peak port pressure on a carbine length system is ~35KSI (35,000 psi)  Attached File |
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Posted: 1/5/2021 11:56:06 AM EDT
[#2]
Quote HistoryQuoted: First post? You won't get enough pressure to cycle the action, but shop air pressure can get it to unlock. What you are proposing is not a normal practice. If you used quality parts and ammo it won't blow up on you. For reference, the peak port pressure on a carbine length system is ~35KSI (35,000 psi) https://www.AR15.Com/media/mediaFiles/173511/Screenshot_20210105-105339_png-1765059.JPG ^^^^^ |
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Posted: 1/5/2021 11:58:02 AM EDT
[#3]
It takes around 14,000 psi at the gas port to properly cycle an AR15 action, so compressed air isn't really an option.
Rounds generate around 55,000 psi at the chamber and that pressure decreases as the bullet travels down the barrel. There are a lot of variables that can affect the actual amount needed. Gas port size, length to port, buffer/spring/bcg weight. Personally, I'd just shoot it. Start with a single round in the mag for the first few, then a couple, then full mags. If you're really worried about it, call the local gun shop and see if they have any GO/NO GO gauges and ask if they'd check your build. |
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Posted: 1/5/2021 12:02:05 PM EDT
[#4]
Just shoot it. If you have any ammo
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Posted: 1/5/2021 12:02:29 PM EDT
[#5]
Quote HistoryQuoted: First post? You won't get enough pressure to cycle the action, but shop air pressure can get it to unlock. What you are proposing is not a normal practice. If you used quality parts and ammo it won't blow up on you. For reference, the peak port pressure on a carbine length system is ~35KSI (35,000 psi) https://www.AR15.Com/media/mediaFiles/173511/Screenshot_20210105-105339_png-1765059.JPG Thank you. That's what I needed to know. I guess I'll just have to use live rounds. And, yes, I have them.  |
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Posted: 1/5/2021 12:10:32 PM EDT
[#6]
Quoted: I began the process of "building my own" AR-15. I'm 90% done with my 1st build. It's been a challenge But I'm getting there. I'll explain more once I can make longer posts. Once I finish, I have a different problem. How to "test fire" it.... Since I live in an urban area, I can't just shoot off rounds to test fire. And I want to test cycle the action safely before going up to the country and testing with live rounds. So I thought, would there be a way to test/simulate the gas action cycle by blowing a shot of compressed air down the barrel, simulating the firing of a round and causing the action to cycle. I would use 5.56 snap caps (and, perhaps even an empty 5.56 shell as the first extraction) and, as long as it was able to cycle properly a few times, then I'd think it safe to test fire with live rounds. Is this something that's normally done? Or do you just go ahead and test with live rounds? The two issues I face with this method are:
How "urban"? Do you have a back yard? |
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Posted: 1/5/2021 12:18:48 PM EDT
[#7]
Quote HistoryQuoted: It takes around 14,000 psi at the gas port to properly cycle an AR15 action, ..... psi and dwell time is what's needed. To do work the gas pressure needs time to act. If the bullet passes gas port at 14kpsi but then psi drops to 5kpsi in 250usec, that will not cycle the bolt. |
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Posted: 1/5/2021 12:19:26 PM EDT
[#8]
Quote HistoryQuoted: How "urban"? Do you have a back yard? Very urban. Yes, I do have a back yard but houses are all on .1 - .2 acres and very close up. And, on top of that, my backyard butts up against a WCE (Wetlands Conservation Easement). In essence, people are allowed to walk through the Easement (not on my property, though). Definitely not somewhere where I can do test firing. |
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Posted: 1/5/2021 12:35:03 PM EDT
[#9]
Quote HistoryQuoted: Just shoot it. If you have any ammo Seriously. There is over-thinking and then there is OVER-THINKING |
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Posted: 1/5/2021 12:40:55 PM EDT
[#10]
Use a blank firing adapter and blanks.
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Posted: 1/5/2021 12:49:09 PM EDT
[#11]
A company my brother used to work for developed this. It's Virtra, a 3D simulation company that provides training for LEO and MIL. However, it was lower-power, mainly to more accurately simulate a pistol/ rifle function as you ran through scenarios. They are sure fun to work with, though.
I know that now Travis Haley offers courses with this system, I visited during the opening of his Scottsdale facility. https://www.virtra.com/overview-le/ |
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Posted: 1/5/2021 1:11:59 PM EDT
[#12]
Quote HistoryQuoted: psi and dwell time is what's needed. To do work the gas pressure needs time to act. If the bullet passes gas port at 14kpsi but then psi drops to 5kpsi in 250usec, that will not cycle the bolt. Quote HistoryQuoted: Quoted: It takes around 14,000 psi at the gas port to properly cycle an AR15 action, ..... psi and dwell time is what's needed. To do work the gas pressure needs time to act. If the bullet passes gas port at 14kpsi but then psi drops to 5kpsi in 250usec, that will not cycle the bolt. True. I should have just left the "gas port" part out. And that number can vary by quite a bit depending on lots of other factors. Point being, a guy isn't going to be able to just chuck up an air compressor or use some canned air and get anywhere close to getting an AR action to cycle. |
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Posted: 1/5/2021 1:30:52 PM EDT
[#13]
Just load one round into the magazine and fire it, if the action locks back on the now empty magazine everything is as it should be.
One round, even in an urban area can be attributed to a tire blow out, firework, some other urban anomlie. |
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Posted: 1/5/2021 1:41:05 PM EDT
[#14]
Quote HistoryQuoted: Just load one round into the magazine and fire it, if the action locks back on the now empty magazine everything is as it should be. One round, even in an urban area can be attributed to a tire blow out, firework, some other urban anomlie. Between my "mower" and "portable generator", we have a lot of "anomalies" in my area. 
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Posted: 1/5/2021 1:44:49 PM EDT
[#15]
endoscope
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Posted: 1/5/2021 1:55:27 PM EDT
[#16]
Quote HistoryQuoted: Just load one round into the magazine and fire it, if the action locks back on the now empty magazine everything is as it should be. One round, even in an urban area can be attributed to a tire blow out, firework, some other urban anomlie. No biggie. Thanks all! |
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Posted: 1/5/2021 2:04:48 PM EDT
[#17]
Blanks?
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Posted: 1/5/2021 3:50:51 PM EDT
[#18]
Quote HistoryQuoted: Blanks? Blanks still make noise, right? And, I don't have a source for them. |
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Posted: 1/5/2021 4:36:12 PM EDT
[#19]
Quote HistoryQuoted: Blanks still make noise, right? Quote HistoryQuoted: Quoted: Blanks? Blanks still make noise, right? Yes. |
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Posted: 1/5/2021 6:51:19 PM EDT
[#20]
Quote HistoryQuoted: Just load one round into the magazine and fire it, if the action locks back on the now empty magazine everything is as it should be. One round, even in an urban area can be attributed to a tire blow out, firework, some other urban anomlie. DO NOT DO THIS. It's most likely illegal, and definitely unsafe. Most municipalities have "unlawful discharge" laws that prohibit discharging a firearm inside city limits. What happens if your makeshift backstop doesn't work as well as you hope? Risking the lives and property of others nearby is not worth the risk to test your firearm. Go to a range or a safe location where it is legal to do so if you want to function test your weapon. |
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Posted: 1/7/2021 9:30:06 PM EDT
[#21]
Quote HistoryQuoted: DO NOT DO THIS. It's most likely illegal, and definitely unsafe. Oh, OK, I guess I will stop....Well, Maybe....  |
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Posted: 1/7/2021 10:34:12 PM EDT
[#22]
When I was younger, well 45 or so years ago now, I had a friend that had a small range set up in his house, his basement actually. 22s mostly. When his folks weren't home he would turn the stereo up, those days it would have been Led Zeppelin or Beatles or Black Sabbath or some such, and he would just fire away. Later years he would even fire his m1 carbine. This is inside city limits, single family house on a street of mixed tenements and single family houses side by side. The police never came. No one ever called them. Now it is impossible to determine if they never heard the shots due to being in a basement and a loud stereo or if they heard them and ignored the neighbor kid.
So, turn the stereo up, get a stack of wood, go down in the basement, set up a back stop and fire away. Then again, you might die from lead poisoning in the air. |
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Posted: 1/8/2021 10:05:36 AM EDT
[#23]
Quote HistoryQuoted: So, turn the stereo up, get a stack of wood, go down in the basement, set up a back stop and fire away. Then again, you might die from lead poisoning in the air. Definitely. Loose some projectiles in a concrete basement at ~3000 fps. What could go wrong?  FFS! |
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Posted: 1/8/2021 10:29:17 AM EDT
[#24]
Quote HistoryQuoted: Very urban. Yes, I do have a back yard but houses are all on .1 - .2 acres and very close up. And, on top of that, my backyard butts up against a WCE (Wetlands Conservation Easement). In essence, people are allowed to walk through the Easement (not on my property, though). Definitely not somewhere where I can do test firing. Just remember this phrase: "I'm glad you're here Officer, I heard those noises too. I think its the neighbor behind me. He constantly lights off those big fireworks. Very alarming. My dog has PTSD." |
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Posted: 1/8/2021 4:00:07 PM EDT
[#25]
I had a range in my basement for a while. .22's, I could shoot all day. 9mm, was loud enough to not be fun. .40 was downright unpleasant. I can't imagine a center fire rifle.
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Posted: 1/8/2021 5:27:14 PM EDT
[#26]
Quote HistoryQuoted: I had a range in my basement for a while. .22's, I could shoot all day. 9mm, was loud enough to not be fun. .40 was downright unpleasant. I can't imagine a center fire rifle. Bullet trap or back stop? What did you use? |
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Posted: 1/9/2021 1:59:48 PM EDT
[#27]
Quote HistoryQuoted: Bullet trap or back stop? What did you use? Quote HistoryQuoted: Quoted: I had a range in my basement for a while. .22's, I could shoot all day. 9mm, was loud enough to not be fun. .40 was downright unpleasant. I can't imagine a center fire rifle. Bullet trap or back stop? What did you use? I used a plywood box filled with rubber mulch. Target area was a 32" cube, completely filled. Cement wall behind it, but nothing ever hit the wall. I had a box fan with a hepa filter on it to eat the smoke and lead. It seemed to work pretty good, base on how much it reduced the smell when I added it. ETA: I hung a piece of rubber horse mat on the front of the box to hang targets on. I took a lot of hits before holes would open big enough to let the mulch fall out. |
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Posted: 1/10/2021 12:11:46 AM EDT
[#28]
Find your nearest sport shooting club with a rifle range and shoot it there
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Posted: 1/11/2021 9:15:48 PM EDT
[#29]
Quote HistoryQuoted: DO NOT DO THIS. It's most likely illegal, and definitely unsafe. Most municipalities have "unlawful discharge" laws that prohibit discharging a firearm inside city limits. What happens if your makeshift backstop doesn't work as well as you hope? Risking the lives and property of others nearby is not worth the risk to test your firearm. Go to a range or a safe location where it is legal to do so if you want to function test your weapon. Trust me, I'm well aware. To operate a home range, one has to have a property that's at least 1.0 acres separate from all other properties. And even that won't stop neighbors from calling the cops if they hear the shots... A huge hassle. Anyway, I finished the build today, so I'll just go ahead and test fire with live rounds at a range, somewhere. |
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Posted: 1/12/2021 6:10:34 PM EDT
[#30]
Good move. Some of the advice suggested here seems like it should be preceded by, “Here, hold my beer.”
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Posted: 1/17/2021 4:58:30 AM EDT
[#31]
Two sleeping bags over the gun. Fire in to the ground. VERY muffled if you have enough material to absorb sound.
Could use anything. A crap ton of blankets, for instance. Make sure the ejection port is not blocked so u can check for functioning. Make sure the muzzle is not IN the ground., Fire one single round. Bob's your uncle. Also any holidAY like New years or July 4th in USA is fair game for guns in back yard. I would not be firing multiple shots even at firework time. Just opne or two to check for function. IN to the ground! Not in the air. |
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Posted: 1/22/2021 4:29:10 AM EDT
[#32]
Quote HistoryQuoted: Use a blank firing adapter and blanks. I would just do this, it really isn’t that loud. |
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Posted: 1/23/2021 1:40:13 AM EDT
[#33]
There are top end air guns out there that use tanks pressurized up to 4,500-PSI
I wonder if you closest the bolt on a fired case and had an adapter to screw onto the barrel muzzle threads and a high pressure high flow ball valve and just "dumped the tank" out of one of those setups if that would work. A lot higher pressure "compressed air" then I think the OP was thinking about. But, approaching it from the theoretical side of the basic question if you used a tank like I have on my souped up "Air Force Texan 45-cal" air gun with the right attachments to get a good strong seal on the muzzle threads and a big "dump valve" I think you could get enough pressure inside the barrel to cycle the action of an AR or most other gas operated guns for that matter. Pressure would still be lower then actual firing but the dwell time would basically be as long as needed till the action cycled and the breach end opened and let the pressure out. Yes, it wouldn't be a perfect seal but I would think plenty good enough if you "dumped the tank" out of a high pressure PPC air gun into a sealed muzzle thread attachment adapter. Heck, even the basic non-souped-up 3,000-PSI setup might be enough to cycle the system. |
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Posted: 1/23/2021 4:25:33 PM EDT
[#34]
Quote HistoryQuoted: Bullet trap or back stop? What did you use? Quote HistoryQuoted: Quoted: I had a range in my basement for a while. .22's, I could shoot all day. 9mm, was loud enough to not be fun. .40 was downright unpleasant. I can't imagine a center fire rifle. Bullet trap or back stop? What did you use? Phone books, 4 Yellow Page with a plywood face. But things were different in the 70’s Edit. Spell check 
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