5.7x28 AR upper, why not?

[Panzerschwein]

Agreed. My wife has serious trouble with 9mm recoil, even from a full size gun that dampens it down some, she's just too small. She carries a 380 ACP in her purse, about the most recoil she can handle. I've got a 38 special tucked away in the kitchen for her with mellow loads that she's good with too. (Figure bad guy isn't going to really care if he's hit at 800 fps vs 950fps... him getting hit in the first place is more important at the moment..)

223 recoil isn't bad *but* the noise when fired indoors is absolutely horrid. Muzzle flash can be eliminated with a Smith Vortex flash suppressor, but still, it's like hitting yourself with the sonic part of a flashbang. (M-8 stun grenade is ~170 decibels, a 20" AR is 160-165db, and it gets MUCH louder from a 16" or 14.5" tube.)

Conversely, a 10.5" PS90 is 158db, and it gets MUCH quieter as you move to the standard 16" barrel.

16" PS90 is still not hearing safe, but it's at least well below the threshhold of a damn flashbang grenade going off less than 2 feet in front of your face in an enclosed space. Which is essentially what your'e doing when you shoot an AR15 223 indoors.

Well, if you say so it must be true.

Truth is, humans experience what is known as "selective hearing" or "audio exclusion" in situations like an indoor shooting. This protects the hearing and many people say they "never heard the shot" if/when they do have to shoot in a home. I know many people who use 7.5-12" SBR ARs for HD work, and they work well in that roll despite what you might think.

 

[MistWolf]

But it doesn't protect your ears from being damaged

 

[ClickClickD'oh]

Truth is, humans experience what is known as "selective hearing" or "audio exclusion" in situations like an indoor shooting.

People CAN experience auditory exclusion during high stress events. It is not a guaranteed physiological reaction nor is it guaranteed to repeat in people who have experienced it before. In fact, the opposite may occur and you may experience increase hearing perception.

This protects the hearing...

No, auditory exclusion certainly does not protect hearing. Physical hearing damage still occurs. The brain simply ignores input from certain non-critical functions to increase processing power for more critical functions.

I know many people who use 7.5-12" SBR ARs for HD work, and they work well in that roll despite what you might think.

Do you know anyone that's actually discharged a 7.5" SBR AR inside a home?

 

[Sam1911]

Truth is, humans experience what is known as "selective hearing" or "audio exclusion" in situations like an indoor shooting. This protects the hearing and many people say they "never heard the shot" if/when they do have to shoot in a home. I know many people who use 7.5-12" SBR ARs for HD work, and they work well in that roll despite what you might think.

I was about to jump on that and point out that it most certainly does nothing to protect your hearing, but it seems folks got to that point ahead of me.

 

[Panzerschwein]

People CAN experience auditory exclusion during high stress events. It is not a guaranteed physiological reaction nor is it guaranteed to repeat in people who have experienced it before. In fact, the opposite may occur and you may experience increase hearing perception.



No, auditory exclusion certainly does not protect hearing. Physical hearing damage still occurs. The brain simply ignores input from certain non-critical functions to increase processing power for more critical functions.



Do you know anyone that's actually discharged a 7.5" SBR AR inside a home?

No but I personally know of several who use them in that roll. They are getting pretty popular as HD weapons.

Regardless if damage does occur or not, the amount of firing needed in that situation would not cause any lasting harm. Sure it might be noisy, but what gun isn't? The effectiveness of the platform far outweighs the fact that it might be louder than some weapons if fired indoors. My point still stands.

 

[ClickClickD'oh]

No but I personally know of several who use them in that roll. They are getting pretty popular as HD weapons.

How do they "use them in that roll"? Does that mean the AR sits under the bed or by the nightstand? Or does it mean that the people actively train with their AR to fill that roll in similar circumstances (shoot houses)? Because there's a hell of a lot of difference between someone who just picks a gun and sticks it under their bed and someone who has run it in the intended circumstances. I've run a 14.5 in a shoot house, and you damn well feel the thing in your chest. It's a loud beast even under plugs and muffs. I wouldn't want to toss off a 7.5 in a bedroom. Popping off an AR in a small room is not at all like popping one off on an open rifle range or even a large indoor bay.

Regardless if damage does occur or not, the amount of firing needed in that situation would not cause any lasting harm.

Do you have MD appended to your name?

If not, I think I'm going to take this guys word for it: Michael Stewart, PhD, CCC-A, Professor of Audiology, Central Michigan University -

"People who do not wear hearing protection while shooting can suffer a severe hearing loss with as little as one shot, if the conditions are right."

 

[Panzerschwein]

How do they "use them in that roll"? Does that mean the AR sits under the bed or by the nightstand? Or does it mean that the people actively train with their AR to fill that roll in similar circumstances (shoot houses)? Because there's a hell of a lot of difference between someone who just picks a gun and sticks it under their bed and someone who has run it in the intended circumstances. I've run a 14.5 in a shoot house, and you damn well feel the thing in your chest. It's a loud beast even under plugs and muffs. I wouldn't want to toss off a 7.5 in a bedroom. Popping off an AR in a small room is not at all like popping one off on an open rifle range or even a large indoor bay.



Do you have MD appended to your name?

If not, I think I'm going to take this guys word for it: Michael Stewart, PhD, CCC-A, Professor of Audiology, Central Michigan University -

"People who do not wear hearing protection while shooting can suffer a severe hearing loss with as little as one shot, if the conditions are right."

All I know is they own and use them for personal defense.

Some of the guys I talk with have been in REAL firefights in Afghan and Iraq.

I think they know what they're doing. Just sayin'.

 

[ClickClickD'oh]

All I know is they own and use them for personal defense.

So, you don't even know if a third party has ever actually fired the weapon in a close indoor environment, but you are willing to personally testify about what the effects of doing so would be?

Some of the guys I talk with have been in REAL firefights in Afghan and Iraq.

I think they know what they're doing. Just sayin'.

Then they weren't running 7.5s. They were either running 14.5s (where in this thread have we seen this number before?) or 20s. They also might not have ever run them indoors and they were most certainly doing so with earpro on.

So go ask your friends if they ever fired their M4s in a 12x12 room and how that went for them.

 

[barnbwt]

Also, I believe the savvy cool kids doing entry work would get some suppressors along with their full auto SBR's

A braked 16" barrel is bad enough to be alongside of (you feel it in your sinuses and eyeballs). I have to assume a 7.5 is quite literally as violent as being boxed in the ears. You may not "hear" the bang, but you sure as hell won't hear anything afterward, either.

Well, except for "EEEEEEEEEEEEEEEEEEEEEEEeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee...:

But only until your get your perforated eardrums stitched back up . I fired my five-seven without ears once in an enclosure. As best I recall, I perceived it as "wWOP!" followed by about ten to fifteen seconds of silence, then a gradual return of volume accompanied by temporary tinnitus and auditory sensitivity for about three days or so. A 223 is a good 25% more pressure, and a hell of a lot more gas volume behind the detonation bubble. An SBR AR15 would likely engulf your entire head in the overpressure bubble.

Also worth noting that a 5.7x28 may in fact be nearly equaling 223 in performance in that type of barrel length (I forget where they actually cross), and with ~1/2 the powder flash and blast.

TCB

 

[MachIVshooter]

Also worth noting that a 5.7x28 may in fact be nearly equaling 223 in performance in that type of barrel length (I forget where they actually cross), and with ~1/2 the powder flash and blast.

Not even close. A 55 gr 5.56mm ball round will still hit 2,500-2,600 FPS from a 7.5" tube. The 5.7x28 can't even manage that speed with half the bullet and an extra 3" of barrel.

The two rounds never cross on the performance scale.

 

[Trent]

Had a negligent discharge once in my early 20's.

Rifle was leaned up against the counter (top facing me), loaded magazine was sitting on top of the counter. Brain said "magazine is out, check the chamber." So I picked it up, put the buttstock on the counter - muzzle was MAYBE 9" in front of my nose. Jack the slide, round flew out, pull the trigger. I skipped the step of checking if it HAD a magazine in it because I saw a loaded one sitting next to it and *assumed* it had already been removed. When... in fact.. there were two magazines; one in the gun and one on the counter.

Saw white flash, couldn't hear anything. Buddy of mine came running in from the other room and grabbed my shoulders, turned me towards him. He's yelling SOMETHING at me, can see his lips moving but I can't hear a damn THING. I lip read "are you OK" and say (yell?) back "YES". Hand him the gun and say "I THINK I SHOT THE CEILING." Had a bloody nose, eyes were watering something fierce. Quite a shock.

Anyway about 15 minutes later I start hearing eeeeeeeeeeeeeeeeeeeeeeeeeeeee... about 30 minutes later EEEEEEEEEEEEEEEEEEEEEEEE... for several days ANY loud noises physically hurt and most noises had a really odd sound to them. One shot and I'd permanently damaged my hearing - I still have tinnitus.

That was one shot, in a large kitchen, with the windows and doors open (summertime) which allowed overpressure to vent a little. If the volume of space had been any smaller ....

Anyway when I say that ANY rifle (223, 7.62x39, 308, etc) is bad news when fired indoors, and that the results are similar to a flashbang on your fragile human system, I'm not joking around about it. Between the volume of gas you are venting, the equivalent loudness between an M-8 stun grenade and the various intermediary cartridge rifle platforms, the effect isn't too dissimilar.

I don't care if you only fire one shot, I don't care if you get auditory exclusion and don't hear it (I didn't), you WILL damage your hearing, and (quite possibly) stun yourself a little. Last thing you need in a gunfight is to lose ALL of one of your primary senses.

A 5.7x28 out of a PS90 will still do this, it's by no means hearing safe when shot indoors unless you SBR it and throw a Gemtech on it, but in stock form it's still nowhere NEAR as loud as a 223 fired from a 16" AR.

 

[mavracer]

A 5.7x28 out of a PS90 will still do this, it's by no means hearing safe when shot indoors unless you SBR it and throw a Gemtech on it, but in stock form it's still nowhere NEAR as loud as a 223 fired from a 16" AR.

Actually if you don't cherry pick data they really aren't that far apart.
In FN's testing the 5.7 was 161 Db, a 16" M4gery with a A2 flash hider is only 162 Db Now if you compare a big 3 gun brake you can get to 165 and above but I wouldn't suggest that for SD.
I'd suggest a linear comp which will drop a 16" AR below 160.
Also just a point of reference DB's scale isnt linear and a 170 Db flash bang is twice as loud as a 160 Db muzzle blast. and just for the record 170 is at the edge of the 5 meter effective range of a FB at 1 meter it's 180

 

[barnbwt]

A cursory Google search...
http://www.sadefensejournal.com/wp/?p=1093


Only a sample of one, but far more scientifically documented than any other study I've ready through on 223.

I can't seem to find such quantified data on 5.7 (also, Quickload apparently sucks at modeling that cartridge) so it's harder to make a direct comparison, but;
-We appear to be talking more like 2200 ft/sec for a 7" barrel, and rapidly dropping at that
-Notably, a 5" barrel is well below the ~2000ft/sec from a five-seven pistol, with a projectile going way slower than designed
-17000psi from a 7" barrel, and seeing how 5.7 is 20% lower pressure to start, and has like 1/3rd the case capacity & powder charge, we can surmise both pistol and carbine have markedly lower pressure than the corresponding 223 numbers.
-For sub-50 grain projectiles, can we at least agree that velocity is the only real number worth looking at for the purposes being considered (i.e. not hunting deer)?

Anywhoooo...all this to simply make the point that the cartridge isn't what we need to be debating for this particular application (plinking, defense, light varminting, general utility). So...as far as the actual platforms that can be debated as far their merits, we only have a few choices;

-AR57
-MPA57
-P90

At least, unless someone besides Masterpiece Arms is making a 5.7x28-anything.

TCB

 

[barnbwt]

In FN's testing the 5.7 was 161 Db

I don't suppose that was from the pistol, was it? I'm just trying to understand the physics of such a smaller-volume, lower-pressure round of the same diameter being anywhere in the same ballpark as 223, as far as muzzle pressure (blast loudness) is concerned

TCB

 

[MachIVshooter]

I'm just trying to understand the physics of such a smaller-volume, lower-pressure round of the same diameter being anywhere in the same ballpark as 223, as far as muzzle pressure (blast loudness) is concerned

dB are in no way directly related to pressure. dB is a logarithmic expression of noise intensity; frequency, pressure, and duration are separate components (no less important). Low dB noises with high pressure can just as easily damage hearing. Likewise, sounds of the same dB rating may be perceived as more intense if the duration is longer (can you imagine a 5 second long gun shot?).

Case in point, a .50 BMG has about the same dB rating that many large magnum rifles produce (about 175), but the quantity of propellant equates to a blast that you can feel considerably further away. Top alcohol dragsters are in the same range, and you can feel that pressure on your chest from well over 100 feet away (and nitromethane dragsters can hit 210 dB! ). Remember, every 3 dB is a DOUBLING of intensity.

 

[Panzerschwein]

I frankly do not care HOW loud a gun is for HD.

To me, like my buddies (many in the SPECOPS community), an SBR tac carbine makes perfect sense for HD work. Extremely compact, manuevearable, massive stopping power vs. any handgun round, room for optics/lights/etc. etc. etc., it pretty much has all basis covered in that role IMHO.

Listen, ALL guns are going to be loud fired indoors. ALL guns are going to cause SOME degree of hearing damage, but in the few shots it SHOULD take to stop the tango, it really isn't going to matter as far as long term hearing goes.

IDK about you, but I will NOT step down to any lesser weapon system than an AR for HD. I would certainly prefer something with about an 11.5" tube, but right now my 16.5 should work fine. Just because it's a little more noisy than some systems doesn't mean I won't use it, because it is the BEST option available in an HD platform time now.

JMHO.

YMMV.

 

[MachIVshooter]

I frankly do not care HOW loud a gun is for HD

You may feel differently if you ever have to use it.

Have you ever fired a rifle, even a 16"+ tube, inside the confines of a 100-150 sq ft. area? It's startling, even with ears on and in full anticipation. That overpressure is confined; you really feel it. Not vastly different from the concept of a firecracker on an open palm vs. clasped in a fist. Even absent perceptible noise, pressure can easily damage hearing. The tympanic membrane is not very tough; just ask anyone who's had their ears boxed. If they had it happen under water, you may have to ask them in writing or ASL.

ALL guns are going to cause SOME degree of hearing damage, but in the few shots it SHOULD take to stop the tango, it really isn't going to matter as far as long term hearing goes.

Look, the dB level of any firearm other than a .22 rifle is well above the threshold of instant and permanent hearing loss.

I'm not saying you shouldn't use a rifle for HD, just be aware of the damage it may do, and take appropriate measures. I, too, keep a 12.5" SBR AR in 5.56mm for HD. I also have a set of electronic muffs right next to it. My 10mm handgun is a primary for investigating noises or if I were to literally wake to a BG in the doorway. It will definitely hurt my ears, but burning 60% less powder and at just a bit more than half the pressure, is nowhere near as offensive as a 5.56mm SBR. If I have time to get the rifle into action, I have time to get the muffs on.

 

[barnbwt]

frequency, pressure, and duration are separate components

They do correlate to each other, though; barrel volume to frequency, duration to 'overbore'/excess case volume and also gas velocity (which in turn is related to pressure), pressure at the muzzle is arguably correlated to powder volume as well (supposedly all powders generate roughly the same volume of gas, from what I've read).

Frequency should be the same, seeing as same bore, same barrel length (for 16" carbine). Pressure is markedly higher in the AR in all lengths; I honestly wonder if the 5.7 isn't getting close to ambient after 16". Duration favors the AR as well, owing to it's larger case volume.

There is one factor that goes unmentioned, though, and that is the overpressure bubble. When a super-sonic high pressure round is fired, a spherical bubble of super-sonic gas is forced from the muzzle, vectorable to a degree by compensators. The boundary of the bubble is a pressure discontinuity or shockwave, with higher pressure air on one side and ambient on the other, with no gradient between them. It is literally like having your ears boxed by a palm if it is large enough to engulf your person; there is bulk force involved due to the pressure differential. Even a super short 223 can generate enough velocity to get the gas bubble formed at the muzzle, and the size of the bubble is directly proportionate to the mass of expanding gas inside the bubble (or pressure & temperature, if you will). The more powder generating the bubble, the farther it can expand before the pressure inside is the same as ambient, and the pressure wave coalesces into a mere sound wave. At the same time, the shorter the barrel, the closer you start to the bubble in the first place.

SBR tac carbine makes perfect sense for HD work. Extremely compact, manuevearable, massive stopping power vs. any handgun round, room for optics/lights/etc. etc. etc., it pretty much has all basis covered in that role IMHO.

Again, this is simply not quite the case in short AR's (sub ten inch). This is common knowledge in even the NFA forum, here, never mind the brief research I did on the subject today.

ALL guns are going to cause SOME degree of hearing damage, but in the few shots it SHOULD take to stop the tango, it really isn't going to matter as far as long term hearing goes.

I'm afraid you would likely be wrong. Remember that hearing loss isn't the problem, but tinnitus; it's driven people to suicide, and is not something to take lightly. FWIW, hearing loss is probably one of, if not the most common injury sustained by our servicemen, and I for one have never understood why suppressors are not more common, nor electronically filtered/enhanced earplugs mandatory in training and hostile areas by this time. I mean, considering how much money we waste on hearing aids after the fact, and all...

"Malp...Malp...Malp... --Sterling Archer

TCB

 

[MachIVshooter]

They do correlate to each other, though; barrel volume to frequency, duration to 'overbore'/excess case volume and also gas velocity (which in turn is related to pressure),

Absolutely true. I only aimed to point out that there is no consistent general equation for dBSI/kPa

pressure at the muzzle is arguably correlated to powder volume as well (supposedly all powders generate roughly the same volume of gas, from what I've read).

Yes, it would be. And yes, smokeless powders, as a rule of thumb, expand to 14,000 times their volume as a solid. I would point out, though, that you have to account for barrel length. All else being equal, a barrel that continues to house the bullet for a longer period of time is going to result in the pressure attenuating further before the projectile exits the muzzle. This is one of the basic principles behind suppressors as well; contain, vector and attenuate the blast to keep a significant portion of it from exiting.

Powder burn rate can, of course, affect this, most notably with handguns; if the powder does not burn completely before the bullet exits, you may have unburned powder exiting the muzzle. If it never burns, it never expands to gas, hence less total pressure. But that is really inconsequential and academic minutia.

Frequency should be the same, seeing as same bore, same barrel length (for 16" carbine). Pressure is markedly higher in the AR in all lengths; I honestly wonder if the 5.7 isn't getting close to ambient after 16". Duration favors the AR as well, owing to it's larger case volume.

Honestly don't know enough about acoustics to speculate about the frequency aspect. I would surmise, though, that myriad factors come into play there, including barrel harmonics, air density, temperature, and so on.

I also don't know that the volume directly correlates with the duration, though I'm inclined to agree with your theory.

There is one factor that goes unmentioned, though, and that is the overpressure bubble. When a super-sonic high pressure round is fired, a spherical bubble of super-sonic gas is forced from the muzzle,

That's not exclusive to super sonic rounds; All smokeless powders expand at a super sonic rate. The component that is unique to super sonic rounds is the sonic crack the bullet produces.

The boundary of the bubble is a pressure discontinuity or shockwave, with higher pressure air on one side and ambient on the other, with no gradient between them. It is literally like having your ears boxed by a palm if it is large enough to engulf your person; there is bulk force involved due to the pressure differential. Even a super short 223 can generate enough velocity to get the gas bubble formed at the muzzle, and the size of the bubble is directly proportionate to the mass of expanding gas inside the bubble (or pressure & temperature, if you will). The more powder generating the bubble, the farther it can expand before the pressure inside is the same as ambient, and the pressure wave coalesces into a mere sound wave. At the same time, the shorter the barrel, the closer you start to the bubble in the first place.

I concur with all but the highlighted portion. Pressure does not make sound, and sound is not a pressure wave. Sound is vibration, which is a change in pressure at a frequency. Air at 1 bar (atmosphere @ sea level) is silent, as is air at 10, 20, 100 atmospheres. Which is why your charged compressor in the garage makes no noise (unless it's leaking). But create changes in pressure, you get noise, such as that obnoxious pulsating when your car window is at just the wrong height going down the road.

But again, pressure and sound do not have a fixed relationship that is easily quantified. Smacking a piece of 1/4" sheet steel with a ball peen hammer is far more painful to the ears than the thud of a bass drum, but creates far less pressure. Conversely, that pulsating pressure created by the partially open car window is painful to your ears, but at a dB level that would be completely tolerable absent the high pressure component.

The science of acoustics is very interesting, and admittedly one that I need to spend a whole lot more time on. Far more complex than most people ever care to discover, for sure. To most, noise is either pleasant or it's not, and they don't really care about the why.

 

[B!ngo]

I think the contributors here covered all of the bases (even when there aren't bases!) but for me my real draw for the round was:
The PS90 itself is the coolest PDR ever created - for HD, short ranges, high-volume conflagrations. You lose all of the cool and much of the small, maneuverable, high-volume with the AR
The round is more interesting if you have the carbine and the FiveSeven so if you don't buy both, then the range toy value is reduced
Whenever you say 'range toy', the answer should always be 'yes' because the term overrides most practical considerations and turns in to an emotional one. Which is not bad at all - and is not meant as a diss. It's just different than, 'tell me which gun will more likely save my family's life?'.
I say do it, but reconsider the PS90 instead and plan on a FiveSeven in the future. And dollar-cost-average your way in to a good stock of ammo.
B

 

[mavracer]

I don't suppose that was from the pistol, was it?

Nope it was a P90 10.4" barrel and they said bare but I'm not sure if they had the factory A2 flash hider or not.
I'm fine with my 16" AR with a linear quiet brake, It may not be perfect situation but it does push most of the sound and blast toward the target. If I had a PS90 it'd wear one too.

 

[4thPointOfContact]

As a PS90 owner - -
I'm rather fond of the 5.7 round for indoor and short-range outdoor protective situations. The small caliber, high velocity round is more likely to break up upon encountering walls than is something like a 9, 40 or 45.

That said, I've also handled a 5.7 upper on both semi and full-auto AR lowers. It loses a little bit in handiness due to the increased weight over the P/PS90 platform*, but if you already have a lower then getting an upper is the lowest cost way to get the caliber. Another possible plus is that by inserting a magazine with the feed lips (mostly) removed, you can hold a full 50-rounds and keep them from getting underfoot.


* most of which was gained back on the full-auto as it had a shortened barrel. Most of the weight is probably in the monolithic Picatinney-railed upper. I wonder what it would weigh if M-loc or KeyMod instead.

 

[barnbwt]

Nope it was a P90 10.4" barrel and they said bare but I'm not sure if they had the factory A2 flash hider or not.

My five-seven pistol only has a 5" barrel and shoots the same round; I wonder why it isn't louder than a 16" AR15?

Meanwhile, my AR70 w/ Beretta slotted FH has a 17.75" barrel and seems louder despite the distance, plugs, and muffs. I must just be perceiving the increased recoil.

BTW, I did some paint mockup, and wow; the AR57 SBR on an SCR chassis does look pretty darn compelling. I sure hope it's actually doable. To think that little thing has the same firepower as something as large as a Thompson w/ 50rnd drum (let's please not debate "but it's a 45" with regards to a select fire bullet hose; it was always the number of shots on target that was important for a Thompson, same as a P90. When multiple hits are a given, the practical differences between cartridges become even more meaninigless)

TCB

 

[browningguy]

Mine is extremely accurate and gets used often for plinking and varmint shooting at night. Lovely gun with essentially zero recoil.

 

[mavracer]

My five-seven pistol only has a 5" barrel and shoots the same round; I wonder why it isn't louder than a 16" AR15?

I doubt that it isn't unless you're shooting AE ammo that stuff is pretty weak and prolly not as loud.