Loose,
I'm not going to do your homework for you.
If you think a .223 bullet will perform the same through a 10-inch barrel as it will through a 16 incher, have at it.
We haven't even addressed the loss of velocity in a 16 as opposed to a 20-inch barrel.
The varmint rifles the 223 was designed for originally had longer barrels, and the military 5.56 was designed for a 20-inch barrel initially.
New ammunition developments for military use have come about largely because of the M4's shorter barrel.
There's a drop between 20 and 16 inches & much more so in going lower than 16inches.
Besides the velocity loss, the shorter you go the greater muzzle flash can be with some rounds, because the powder charge intended to burn completely in a 20-inch or so barrel simply can't burn as much of its powder in the shorter barrel, which means more of it'll burn out in front of the muzzle. That doesn't help if you need to use the gun in the dark.
The military is now swinging in the direction of heavier bullets for the 16-inch M4s that are widely issued, at least partially because of stopping failures with the lighter projectiles in those shorter barrels.
You may notice the heavier Black Hills OTM had the least velocity loss in my chronograph testing, but still showed a 500 FPS drop.
Percentage figures can be useless, taken out of context.
A percentage can be very deceptive.
If I said I shot two rounds out of a given gun & one misfired, I could say that round produced a 50% failure rate, which would be true. Taken out of context, with no mention of the actual numbers used, the 50% failure statement is highly misleading, in this case because of the limited sampling used.
Closer to the point here, if a small bullet is designed to perform (expand, fragment, etc.) at a certain high velocity rate, a 22% loss of velocity can be very significant, IF the initial velocity is relatively high.
If a larger bullet that's designed to travel at less than half that speed loses 34% of its velocity, the percentages do not translate directly & do not have the same significance.
In comparing the .357 & the .223 in handguns, percentages are meaningless. The actual velocity figures are more useful.
Your sarcasm is also less than helpful. Nowhere did I say being struck by a .223 at 2470 FPS would make an attacker laugh.
I'm saying I see no reason to further dilute the ballistics of the caliber by robbing it of the velocity that it depends on for maximum effectivness.
The 2470 FPS figure is only part of the reason why I say an AR pistol is a poor choice.
You render a defensive caliber weaker, you try to make a large & ungainly platform into something it does a poor job at, and you handicap yourself in the entire process.
No articulable reason for understanding why the pistol AR doesn't cut it in the real world?
It is:
Heavy, requiring two hands for most uses.
Bulky.
Harder than a real handgun to move around dynamically in engaging targets, work around corners, hold steady on target, and so on.
It suffers from the same problem a stockless pump shotgun has- harder to aim, harder to control.
Even with a pad & using the buffer housing against the cheek, it's not as accurate or controllable as a stocked carbine.
It can't be holstered or concealed without going to great lengths to dress for it.
In a car, it can't be utilized as quickly against close threats as a conventional handgun.
There's the muzzle blast & flash to deal with.
And so on.
As I said- you try taking one of those things to a good shooting school & see for yourself just how much of a handicap you create.
Can you complete the course?
Yes.
Will you keep up with the rest of the class?
No.
Is that relevant?
Most certainly.
Every year students show up at carbine classes, as an example, with all sorts of cool stuff bolted on. By the end, much of it's removed.
The students find out directly what's actually useful & what only looks cool.
I spent an entire career clearing buildings for a living.
I've been through excellent training classes & I've been an instructor for my last PD.
Again- there's a reason why these things are not recommended by instructors or used by PDs, and I've already told you what it is.
If you want to bet your life on one, it's your life.
On the submachineguns with collapsible stocks- yes, those are for storage & transport, not for firing in a collapsed position, unless there's a reason to.
ARs with sliders are not intended to be fired with the stocks in their shortest position, unless its shooter is small enough or bulkily armored enough to make it necessary.
My semi-auto Polish AK underfolders are CAPABLE of firing with the stocks folded, but not intended to be.
Submachineguns also tend to be in a class by themselves in certain areas.
They are employed a bit differently than semi-auto handguns of any type.
Why do these AR pistols really exist?
Partly because somebody thought it might be fun to do, which is fine.
Mostly because there's a certain market segment that'll buy 'em because they THINK they're something they're not.
Just because a gun exists doesn't mean it's a good idea, or worth using to defend your life. As a toy, again there's no justification needed.
The overriding motivation for manufacture in this case is that if a maker makes it, enough of you will buy it to put money in the maker's pocket, which is the true bottom line.
Fast,
You're right in that cartridges can be tweaked to offset the velocity problem, but most people who buy an AR pistol just buy the same ammunition they'd normally buy & expect it to work the same in a 10-inch barrel as in a 16 or 20-incher.
Which it doesn't do.
Fortunately, most will never have to find out the hard way in an actual life-threatening situation.
I've talked to a federal agent who was shot by a .223. Even through a full-length rifle with a "good" torso strike, it can be survivable, as battlefield reports are showing today. Weaken it and it can be even more so.
I've also seen the news footage of him being brought to the ER. He was conscious, not real happy, but appeared to be fully capable of continuing the fight at least briefly after he was hit, if he'd needed or wanted to.
Luckily his fellow agents carried on for him.
Denis
M2, it compares poorly to a real handgun, as I said above.
