5.7x28 AR upper, why not?

[barnbwt]

The speed and pressure accelerates is constantly accelerating the bullet.

I get your jist, but it's solely pressure that's driving the bullet (and gas) forward, and acceleration is continuous, but hardly constant (which is why a long enough barrel will slow a cartridge).

If and I say if, the 5.7 had super-duper slow powder that magically ignited and burned out at the same rate across the barrel length (making an arc-shaped plot of burn rate), we'd have something closer the situation of high pressures occurring near the end of the barrel length. But chemical kinetics (which I for sure don't claim to know hardly anything about) indicate conflagration should occur way, way faster than the taper off (I think it's like a fourth-power thing, if memory and chemical formulas are being remembered correctly) --almost instantaneous in comparison, in fact. So the actual internal ballistics is closer to the idealized scenario in which pressure is instantaneously peaked (necessarily at a higher-than-factual level) and drops precipitously as the bullet moves, quickly flattening out as the total volume increases and pressure approaches ambient.

As much effort as FNH put into the cartridge, I would not put a binary or variable-rate powder concoction past them, but evidence does seem to suggest the 'secret ingredient' is merely some really fast pistol powder.

TCB

 

[MistWolf]

I get your jist, but it's solely pressure that's driving the bullet (and gas) forward, and acceleration is continuous, but hardly constant (which is why a long enough barrel will slow a cartridge).

It's also the velocity at which the gas will expand. The projectile will always travel slower than the velocity at which the gas will expand freely.

You are correct about the technical definition of "constant rate". It would have been more correct if I'd said "continuously", but in my defense I did not say "constant rate" I said "constantly"

It is understood that, while longer barrels give more velocity because the gas has more time to accelerate the bullet, there is a point of diminishing returns. At some point, the gas can no longer accelerate the bullet and it will start losing velocity.

I couldn't find a pressure graph for the 5.7, but pressure graphs look very similar regardless of caliber-

30-06
View attachment 703139
View attachment 703140

300 Winchester Magnum
View attachment 703141

38 Super
View attachment 703142

There is always a rapid rise and peak, followed by a parabolic shaped drop

 

[bikemutt]

MistWolf, thanks for explaining the underlying Physics of the matter.

Here's the YouTube video where the author shoots a 5.7 pistol with the Guardian 22 (G22) suppressor. The comment is where the pressure is mentioned: http://www.youtube.com/watch?v=XneDPIU2bD0

Published on Mar 29, 2012
Listen to the difference! I shoot with the suppressor on and off.
This is the Guardian 22 by Huntertown Arms in Indiana. This small, light .22LR suppressor works great on the 5.7 pistol. It will not handle a 5.7 cabine. Too much pressure.
Hear more Huntertown suppressors here:

On Huntertown Arms website they rate the G22 for 5.7 with an asterisk stating only serial numbers greater than a certain value are included. They don't qualify it further by barrel length but it's possible the rating was rendered before carbine length barrels materialized.

My suppressor's serial number indicates it may not be suitable for use with 5.7 but I've also sent mine in to have the aluminium baffles replaced with stainless steel, they also upgraded the end caps at no charge to current production ones. In other works, it's possible mine may now be OK to use with 5.7. I've left them a voice mail asking if my specimen is safe to use with 5.7 and if not, can it be upgraded to handle it. I waited so long for that suppressor I really don't want to blow the darn thing up, or myself for that matter.

 

[barnbwt]

It's also the velocity at which the gas will expand. The projectile will always travel slower than the velocity at which the gas will expand freely.

Yes, and why does the gas only expand freely so fast? Because the reacting propellant's energy/gas production can only generate so much pressure so rapidly (and you can't accelerate the bullet instantly, so to transfer energy to the bullet, it has to move, meaning the chamber volume has to increase rapidly --catch 22, which limits what we can do with nitrocellulose). Two sides of the same equation.

I personally think this is also why 4.6x30 (H&K MP7) is so much more inefficient as a cartridge; the bullet's are often the same mass as 5.7, since mass decreases slower with bore diameter at these itty bitty sizes, but can barely be driven to the about the same speeds by an even larger powder charge and higher pressure. It's like the opposite of a sabot.

TCB

 

[Trent]

Physics disagrees, Trent. Peak pressure occurs where the bullet meets the greatest resistance and that's where it begins it's journey in the rifling.

... Then why does the 300 Win Mag graph you post later clearly show peak pressure at the 3 inches down the tube?

To support what you are saying ALL of the powder would have to burn before the bullet starts moving, and it simply does NOT do that.

For hot pistol powders it may hit peak at .1" past the throat, but for slower powders that may be much further down the barrel; several inches.

E.g. pack a 45 ACP case full of H1000 (slow magnum rifle powder) and won't that pressure will still be ramping up (slowly) until the bullet falls out the end of the barrel?

 

[dprice3844444]

1. i think it would be a great setup for in house personal defense.enough penetration to get the job done,and less of a chance for over penetration like the hotter caliber.50 rounds,no reloading.
2.you can make a pouch setup under the mag well to catch the empties.

 

[barnbwt]

Then why does the 300 Win Mag graph you post later clearly show peak pressure at the 3 inches down the tube?

Doesn't win mag have a ton of extra powder relative to the barrel/chamber volume (over bore) that has to be burnt to reach peak pressure in the first place? Powder that is far, far slower than 5.7 would ever use in the first place? That extra time gives the bullet the chance to move further (albeit under less-than-peak pressures)

I agree that even a 5.7 bullet has likely shifted or even left the case by the time the powder has fully conflagrated, but not inches down the bore; not without extremely slow (think 'punky') powders that would probably never ignite well in the then-too-voluminous (low pressure) interior. Powder has to be closely packed to burn well, and you can't get that in a 5.7x28 if the bullet is inches down the barrel, doubling or tripling the initial case volume.

The other thing is that it'd be extremely difficult to measure and corroborate stuff happening in the first .1" of bullet travel; too much happening too fast for instrumentation to capture well.

All that junk said... Trent has done a ton of reloading and experimentation with the 5.7, so I imagine he has as much data as anybody out there, which is really all we have to work with since the little round's internal ballistics apparently can't be accurately modeled with software (yet). We really need to find someone with a chrono and a Contender in 5.7x28, so I can get a test barrel made that can be cut progressively shorter. If we can back the curve out to the first inch or so, I think that would tell us a lot about how the round does its thing, and what, if any, potential there is to be gained by reloaders or gun designers. But perhaps here's a reason all other duty-pistol cartridges have pistol barrels of ~5" and SMG barrels of ~10", just like the five-seven and P90 (MP7 is 7", making it an unpleasant compromise of ballistics and flash/boom/inefficiency)

It may be moot in any case, since a pistol barrel shorter than 5" will only get louder and flashier than it is now, longer ones can't be carried easily, barrels under 16" for carbines won't find much of a market in any case, and I doubt there's much to be gained in going longer than 16" for such a small powder charge.

EDIT: The real solution for better performance from the carbine would be to get a smaller primer in the cartridge. At that point, the case head is strong enough for higher pressures, and the small bit of powder would still have plenty of time to burn from the now-weaker primer charge over the course of a 16" barrel. A 5.7x28 peaking at 60,000psi vs 50,000psi would climb to different heights than the present case allows. According to a fellow on barfcom who made a gas-op 5.7, increasing pressures much at all loosens the primer pockets and ruins the brass

TCB

 

[barnbwt]

like the hotter caliber.50 rounds

Wait, wut? You're not considering an AR50 upper, are you?

TCB

 

[MistWolf]

... Then why does the 300 Win Mag graph you post later clearly show peak pressure at the 3 inches down the tube?

Look at the pressure rise. If not for the restriction of the bullet entering the rifling, pressure would never rise like that. Neck tension isn't enough to hold the bullet to cause any real spike in pressure

To support what you are saying ALL of the powder would have to burn before the bullet starts moving, and it simply does NOT do that.[/qoute]
Not so. The primer by itself creates enough pressure to push the bullet out of the case and into the rifling

For hot pistol powders it may hit peak at .1" past the throat, but for slower powders that may be much further down the barrel; several inches.

Pistol powders burn too quick and pistol cases don't hold enough powder for that to happen

E.g. pack a 45 ACP case full of H1000 (slow magnum rifle powder) and won't that pressure will still be ramping up (slowly) until the bullet falls out the end of the barrel?

The slowest of pistol powders still have a quicker burn rate than the fastest of rifle powders.

When smokeless powder begins to burn, it does so rapidly. It makes very little pressure unless contained. Case neck tension alone isn't enough to allow pressure to build to any significant degree. When the primer is ignited, not only does it start the powder to burning, it also pressurizes the case and it's possible the primer will start the bullet before the burning powder has built enough pressure to push the bullet on it's own.

The bullet leaves the case but is stopped a short distance later at the leade where the throat meets the rifling. The bullet's acceleration is lowed at this point. More force is now required to push the bullet and pressure rapidly rises. Once the pressure gets the bullet accelerating again, pressure is relieved and begins to fall off. If there is enough powder behind the bullet, pressure can build faster than the increasing volume can relieve it which shows as a continued rise, but it is still falling off. You can see this phenomena in the pressure graph. The peak curve is much gentler, less sharp, than with smaller cases.

It's very important to understand this, especially as a reloader. If that spike rises too rapidly, even if it does not exceed maximum allowable pressure, it will cause a catastrophic failure. This is why quick burning rate powders are limited to small capacity cases. If used in a case too large, pressure will rise too rapidly.

We can see this work with seating depth. Bench rest shooters often seat their bullets so they are very close to or even touching the rifling when the round is chambered. There is very little to no bullet jump to slow the pressure spike. Powder charge must be reduced to keep the pressure rise from being too quick as well as keeping pressure within acceptable limits.

Roy Weatherby went the other way. He used long leades with his magnums to increase volume during pressure rise. This allowed the use of more powder for increased velocity while keeping pressure rise and peak pressure at safe levels

 

[barnbwt]

If that spike rises too rapidly, even if it does not exceed maximum allowable pressure, it will cause a catastrophic failure. This is why quick burning rate powders are limited to small capacity cases. If used in a case too large, pressure will rise too rapidly.

Fast powders (like blank powder, as an extreme example) burn so fast the chamber volume can not adjust via bullet movement fast enough to keep pressures from reaching dangerous levels. I'll need some explanation as to how the rate of application of the breech thrust itself would cause failure, though, since I'm not aware of 'jerk' (force derivative wrt time) having much effect on steel failure apart from fatigue acceleration. Even blank powder isn't a true 'explosive' that would put impact loading on the action.

I always thought Weatherby's had long throats so that a wide array of heavy bullets could be used safely?

I must say this is fascinating talk; we should really get the mods to split it off around post #64 or so

TCB

 

[hso]

as the bullet travels along the barrel, the volume increases

Yes

As volume increases, pressure decreases

That's true, but oversimplified for a system where the powder is still burning and contributing expanding gas to the equation.

Pressure also decreases because the gasses are also losing heat.

True, but irrelevant for a system as small as the rifle of a barrel and one in which the powder is still burning to produce expanding gas.

The reason the bullet comes out faster is because the gas, without anything to restrict it's speed, expands at a constant velocity of about 5700 feet per second.

Where's 5,700 ft./sec come from for the initial sound speed of the propellant? a0 may be the initial speed of the propellant, but the max velocity is still impacted by the friction of the bullet in the bore and the burning powder contributing against the increased volume of the bore.

The speed and pressure accelerates is constantly accelerating the bullet.

I'm not sure what "speed and pressure accelerates it(sic) constantly accelerating the bullet" means. The bullet is like a piston and the barrel is the cylinder. The powder burns causing expanding gas to push against the bullet. The bullet moves because the pressure overcomes the static friction of the bullet in the chamber and the first stage of the rifling. It accelerates from V0 in the chamber and continues to accelerate up to a point. A long as the pressure of the gases from the burning powder overcomes the sliding friction of the bullet in the barrel the bullet accelerates. At some point enough powder is burned where the pressure isn't increasing due to the increasing volume of the barrel and the end of the burn of the powder and the bullet MUST begin to slow against the sliding friction of the bullet in the barrel. A max velocity is reached and more barrel only slows the bullet as the pressure falls off much more rapidly with the increasing volume of the barrel and lack of expanding gases. This is why muzzle velocity for a longer barrel can be slower for the same round than a shorter barrel since the powder has burned enough for pressure to start to drop rapidly. If the pressure isn't maintained above a point to overcome the friction of the barrel the bullet can not accelerate and will begin to decelerate as the barrel friction slows the bullet.

Once the bullet gets going, there doesn't need to be as much pressure to keep accelerating it.

Yes, the static friction is much higher than the sliding friction and once moving the friction is less.

It's that old Newtonian physics at work for ya- Objects in motion tend to stay in motion; Objects that are not in motion tend to stay motionless.

No, but yes. Kinda Newton's first law, Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it, is for uniform motion without external forces and a bullet in a barrel is anything but. The bullet's motion against the pressure of the expanding gases from the burning powder is opposed first by the static friction in the chamber. Once that is overcome it begins to move, but opposed by the sliding friction of the barrel. As long as the pressure from the expanding gases just exceed the friction forces on the bullet it will accelerate slowly, but the pressure is well above the frictional forces and the bullet accelerates rapidly. If the pressure was only from the initial pulse from the firing it would accelerate up rapidly and then rapidly slow (think squib) before leaving the barrel, but the powder burns for a period of time long enough to keep pressure against the bullet in the barrel until the powder burns and the volume in the barrel is too great. At that point the pressure falls off and eventually cannot overcome the friction. Too little barrel and the unburned powder burns outside the barrel wasting the energy on a bright flash and not accelerating the bullet and too much barrel causes the bullet to slow dramatically. It is not as simple as "good old Newtonian physics" by a "long shot".

 

[barnbwt]

Although Newtonian physics (or rather, kinematics) do describe those things pretty well. I don't care to get into the stupidly-nitty-gritty as far as ballistics so close to the chamber that powder is burning, because that's in the realm of aerothermochemistry, a field I took an elective class on and learned enough to know I never want to think about it again. Hypersonic fluid dynamics combined with advanced chemical kinetics

I'm more interested in the useful figures that may be gleaned from analyzing the "end result" of the powder burn cycle, which in the case of 5.7 is likely not far beyond the throat at all for normal loads. Once the powder is at least no longer reacting, it's a lot easier to figure out the rest of an already complicated situation. No need to make a science project out of something that can be measured. I really will have to make a test barrel and get some SS197SR chrony readings in the process of my MP57 build, so that other makers might at least have some data to design competing platforms around and keep the round alive.

The more I learn about it, the more my opinion changes; I initially thought 5.7x28 had trouble taking off because FNH refused to license ammo production to other companies, but now I know that everything from making the ammo to designing new guns for it is incredibly difficult to do without having access to the extensive ballistics research data FNH doubtless had to generate for itself in the first place. If Quickload can't develop an accurate pressure spike, how is a company supposed to develop a competing platform without spending enormous R&D dollars duplicating that effort?

TCB

 

[Trent]

OK at this point I'm just along for the ride, interior ballistics master session in progress...

 

[MistWolf]

hso, heat does play into internal ballistics. A really cold barrel saps heat from the gases, which due to the laws of thermodynamics, lowers pressures and reduces velocity. That's why the original rifling twist of 1:14 for the M16 was changed to 1:12. In arctic conditions there was enough loss of velocity from chilling the barrel and the powder that the bullets were unstable.

I didn't say 5700 fps was the speed of sound, I said the speed of the expanding gasses for smokeless powder is a constant of about 5700 fps. You can research the subject and verify it for yourself. I believe it was a Lyman reloading manual where I first came across this fact. NOTE: One internet author claims the speed of the expanding gas is 5 times the muzzle velocity of the bullet. This is incorrect.

Having to overcome friction is part of Newtonian physics. Although there is friction between the bullet and the bore, if the bullet has enough momentum, it will continue to coast down the bore without pressure from the gas. Much like pushing a cardboard box full of books across a concrete floor. Because of the friction and the box being motionless (motionless object tends to stay motionless), you would have to push hard to get that box moving. But once it is moving, it takes less energy to keep it moving (object in motion tends to stay in motion). Get it moving fast enough and stop pushing, momentum will keep the box moving until friction stops it.

Just because it's rocket science, doesn't mean it's complicated

 

[barnbwt]

Mistwolf, as a 'rocket scientist' I can assure the process is anything but simple. Like all things, it can be broken into bite sized chunks and analyzed, or approximated as closely as we care to. But it's still a field, after 150+ years of study, that still isn't fully understood (seeing as we only recently discovered that short fat cases with sharply tapered necks are far more efficient than the long-neck brewsky of a 30-06.

I thought the 5.56 tumbling issue was due to cold weather not allowing the powder to react fast enough (so slower bullets) as well as the outside air being much colder (denser) which also has the effect of making the bullet behave like it is moving slower (same as how denser flesh causes it to tumble).

As fast as a bullet is fired, you'd think heat transfer would be nearly negligible as far as effecting ballistics, but the gasses are so hot that the same transfer happens really fast, too. It'd be interesting to see how much it really changes things (like if it would cause stringing as the barrel heats up), but my instincts tell me it is a pretty minor factor in most cases. 5.7x28 may not be one of those, however. In any case, all barrels are steel, making it a constant factor, but a ceramic bore might be far more efficient for all we know.

TCB

 

[Trent]

hso, heat does play into internal ballistics. A really cold barrel saps heat from the gases, which due to the laws of thermodynamics, lowers pressures and reduces velocity. That's why the original rifling twist of 1:14 for the M16 was changed to 1:12. In arctic conditions there was enough loss of velocity from chilling the barrel and the powder that the bullets were unstable.

I don't think that's a function of hot gas meeting barrel; I think that's due more to the powder *itself* reacting differently under lower temperatures.

Older, conventional powders are HIGHLY sensitive to cold, but that's not a function of flame temp interacting with bore. Good modern powders do not do that; my point of impact and velocity using H4831SC on 300 win mag did not change whatsover between -24F and 95F when I tested under both conditions this year, cold barrel or no, my first shot was dead on at the start of each string. Velocity did not increase, and the barrel did not walk, even when I was using it as a handwarmer.



If your theory about gas temps cooling were true, I couldn't put together a 20 shot 300 yard group (starting with a cold bore) at -24F without experiencing that phenomenon as the barrel warms from ice cold to blazing hot.

Clearly my wind reading skills need a bit of work, and I had one "whoops" shot fly high on shot 17 where the shivers made me jerk the trigger too early.



But there's absolutely no evidence that bore temp affects powder burn whatsoever, there. And if there WAS a scenario where bore temp was affecting powder burn, it'd be more evident on a long 24" barrel with slow burning powder, like I was using, than any other platform.

Some older powders burns slower when cold. If this phenomenon were due to the flame temp interacting with the bore temp *all* powders would do that and the velocity would increase as the barrel warmed. Even on the older powders you do NOT see that, unless you leave the cartridge in the gun to warm the *powder itself*. There's zero doubt that it's the *powder temp* that matters on those, as far as the effect it has on velocity.

Old Military powders (WC844, etc) are *horrible* when it comes to temperature sensitivity. But that has nothing to do with bore temp (otherwise the effect would wear off as the bore increased.)

If you pre-warm the cartridges (either by leaving them in a hot chamber for a spell, or against your body), the effect is neutralized, cold OR hot bore notwithstanding.

 

[Sam Cade]

A really cold barrel saps heat from the gases, which due to the laws of thermodynamics, lowers pressures and reduces velocity. That's why the original rifling twist of 1:14 for the M16 was changed to 1:12. In arctic conditions there was enough loss of velocity from chilling the barrel and the powder that the bullets were unstable.

That is completely wrong. 1:14 only marginally stabilized the projectile and wasn't enough to keep it point forward when it was passing though the denser arctic air.

If your theory was true once the barrel heated up the bullets would stabilize.

They didn't.


http://www.nennstiel-ruprecht.de/bullfly/gyrocond.htm

 

[MistWolf]

Actually barn, we have known for a very long time that the theoretically ideal combustion chamber is spherical with the ignition source in it's very center and that short, fat cases are closer to that ideal than long skinny cases. That's one theory as to why the 308 Winchester is inherently more accurate than the 30-06. But case shape is also affected by other requirements- magazine limitations; reliable feed, extraction and ejection and other considerations. I'm not saying all rocket science is simple, just that being rocket science doesn't automatically make it complicated As an Aviation Technician, I understand and appreciate that things can be broken down into smaller parts to simplify things. Trying to grasp how an entire jetliner works is over whelming. But taking one system- say the propulsion (engines)- and breaking it down into it's subsystems, components and the basic physics that makes it work, is a big start

The arctic cold did affect powder burn rate and air density but the loss of velocity resulted in enough loss of bullet rpm that stability problems showed up under those conditions.

Trent, powder sensitivity to temperature changes does play an important role in pressure variations just as you point out. British hunting calibers used in tropical conditions were large cased and low pressure (by modern standards) because the heat in Africa and India would cause unpredictable pressure spikes. Ammunition loaded to maximum pressures would give dangerous spikes from the heat.

A cold barrel pulling heat from the gas will have more affect on smaller capacity cases than larger ones because the larger cases hold more powder and produce more heat

 

[MistWolf]

Sam, there was also loss of velocity because of how the cold affected the powder. So it was a combination of things- reduction of RPM (due to velocity loss) and denser air plus the fact the 1:14 twist was marginal to begin with. Sapping heat from the gas is one factor, not the factor. All combustion driven engines (including firearms) operate more efficiently within a certain operating range. That why they work best when they reach operating temperatures but must be kept from overheating

 

[Potatohead]

Wow, this thread has gone sideways.

 

[Trent]

Wow, this thread has gone sideways.

Most threads on 5.7x28 platforms / ammo DO go sideways, and fast.

I'm just pleasantly surprised this one didn't result in any infractions, suspensions, or bans.

 

[barnbwt]

<deleted> But this is supposed to be an AR57 thread, so it'd be cool if mods would split it.

Trent, was your subzero ammo itself held to a set temperature, or was the powder as cold as the bore? It appears that at least for rifle power rounds, barrel heat transfer is negligence --I figured as much. I wonder if temp variance effects might be more profound in 5.7 for a number of reasons (namely, stability in the denser atmosphere)

TCB

 

[Trent]

<deleted> But this is supposed to be an AR57 thread, so it'd be cool if mods would split it.

Trent, was your subzero ammo itself held to a set temperature, or was the powder as cold as the bore? It appears that at least for rifle power rounds, barrel heat transfer is negligence --I figured as much. I wonder if temp variance effects might be more profound in 5.7 for a number of reasons (namely, stability in the denser atmosphere)

TCB

The powder on those shoots was as cold as the bore to start. The rifle and ammo both were allowed to acclimate to the outdoor temps slowly (to avoid frosting my scope lenses, that's a sure way to ruin your day, in subzero temps).

I hammered through the 20 shot strings in ~10 minutes or so, which is enough to seriously warm the 300 win mag barrel. Rounds were left in for varying amounts of time (depended mostly on sight picture, how long it took to calm me down from reloading, etc). The barrel warmed to the point it was hot to the touch (made a GREAT hand warmer wearing gloves, just grab the barrel and instant "ahhhhhh ooooooohhh".)

Powder that's temp insensitive just don't walk as the temp changes. If the BARREL has defects, it surely will walk as it warms. (why I sold my weatherby, thing was only good for 2 shots before it started walking off the paper.).

That krieger barrel I had put on my Savage rifle does NOT budge from point of impact though - no matter what I do to abuse it.

I didn't notice anything odd when I tested PS90 in cold weather in January. I shot it in temps down to 11F. It still shot just like it was summertime out. Didn't notice any point of impact shift with SS197 or AE ammo from when I'd shot it in matches that summer (in 90 degree weather).

 

[barnbwt]

Kewl. Sounds like modern powders really don't have an issue with cold weather (granted, hot weather most certainly does have an impact on pressure & therefore velocity levels, especially if storage is factored in). Kinda makes sense, because nitro-cellulose is a plastic, and plastics are pretty stable below their degradation temperature. Nitro is known to degrade increasingly rapidly above (IIRC) 90deg or so, and it reacts increasingly aggressively in +100deg temperatures. It's actually made me worry quite a bit for our guys in uniform; I've seen what happens to Kydex aircraft interior panels when they come back (think Pringles) indicating over 120deg temps in the aircraft that are supposedly looked after more carefully than random ammo crates.

(made a GREAT hand warmer wearing gloves, just grab the barrel and instant "ahhhhhh ooooooohhh".)

And that's how you frost a scope, right? What you need is a hot water bottle powered by a Vickers, and you can shoot in comfort all winter

TCB

 

[Ar180shooter]

As a range toy:

I had one, and reloaded for it for a short time, but it just bored me. The caliber would be more fun/useful in a bolt gun or Contender IMHO. The upper was heavy for such a small caliber. I would just as soon shoot my .22 LR AR. Too bad there isn't one readily available in .22 Mag.

I enjoyed my 9MM AR a great deal more, it is simpler (A great deal simpler) to reload, factory ammo is cheaper, brass is plentiful.... I could go on and on.

As a range toy it simply did not make the cut.

What I'd love is a .17WSM AR-15. It would be the ultimate Coyote slayer.