Quoted:
Okay, open challenge:

We need a live-fire video of the 15-MOA effect in a non free-float gun.  Maybe 5-shot groups at 100 yards shot rested with no pressure on the forearm or barrel vs groups shot to the same POA with the gun slung, rested against the forearm, rested against the barrel, maybe even one with some sort of constant extreme force exerted on the barrel.

Quoted:
I know I'm possibly making myself a target by not completely piling on after seeing the otherwise unanimous response to this thread, but regardless of the merit of a FF on a military issue rifle, I can confirm that I measured a 9MOA shift with my AR last week by resting the muzzle end of the barrel against a barricade.

I run a 12" FF rail and usually can get part of the rail against a barricade for stabilization (when allowed) when shooting smaller targets in 3gun matches. At a recent match I was missing some of the 1-2MOA targets from a new-to-me barricade where I only had the option of resting the barrel on the barricade due to my setup (I usually don't miss so knew it had to be the gun). I at first didn't appreciate why as I run a heavy fluted barrel on my match rifle and felt the shift wouldn't be as large as I'd experienced on other guns, but as I could see my shots impacting high I just aimed low for hits and thought maybe I'd had a shift in my POA from dialing in the correction for the previous stage at 20 yards. But to pin down the problem I did some testing afterwards at my local range and discovered a 9MOA shift up in my POI when I rested the muzzle brake on a block on the bench. My group size was not impacted, just its location.

The easiest solution in my case is to remove my fore grip if I go back to that range so I can push the rifle farther forward when leaning over that barricade so I can get the FF rail to the support point on the barricade. I'll just have to practice firing that rifle without the fore grip as I've gotten used to it being there.

So, I'm not addressing the rest of the OP's talking points, but I will support that a sizable POI shift can occur from resting the barrel for support. Realize that resting on the muzzle end can more than double the moment arm from what a sling can or what resting a non-FF fore end can, so the resulting POI shift will be correspondingly larger. Get into the cantilevering of the barrel and the often smaller cross section of the forward part of the barrel and my test configuration is a worst case condition, but it does support the statement that large POI shifts can occur when imparting normal forces on the barrel.

Quoted:
The AK-12 features a free float barrel, which I believe this makes us the last first world country to employ a general issue rifle that still retains a non free floated barrel.

Quoted:
Here are some recent pictures from Modern Firearms, which is a great website for Russian guns (and other guns, for that matter).

AK-12 2016 version:
http://modernfirearms.net/userfiles/images/assault/rus/1473444610.jpg
There just isn't much here that hasn't been common in US civilian AKs for years. Free-float rail, railed dust-cover, better grip and stock. The better gas system might be good, and it looks like it might be adjustable which is nice. But it's a fairly minor improvement and probably not worth the effort to replace the AK-74.

The most recent AEK picture I could find, from the 2014 trials:
http://modernfirearms.net/userfiles/images/assault/rus/1416852320.jpg
The stock, grip, and sights have clear HK influence (not a bad thing for its purpose). The balanced recoil system is one of the few actual innovations in firearms in recent years, if it actually works. So far the tests I've seen look very promising. The question will be if the Russians actually issue them in real quantities.

I see nothing here that outclasses the M4. They are both heavier by a couple pounds. Only the AEK shows any chance of being a significant improvement over what it replaces, and I don't recall many HSLD units around the world adopting AKs of any sort over the M4 when given the chance.

Quoted:
So....if it's virtually impossible to hit a target at 100m with an M4 (due to its non floated barrel), how did I (and everyone else) hit the 300m targets during BCT so easily?

Marines hit at 500 if I'm not mistaken, which should be impossible according to this.

Quoted:


The M4 with m855a1 is something like a 1.5-2.5moa gun.

The issue is forces exerted upon the rail is imparted to the barrel, which can shift point of impact 15moa.

So the gun will still shoot with decent groupings, they just won't be anywhere near where you are aiming.

Quoted:


How many moa is that at 500 meters?

Quoted:
So....if it's virtually impossible to hit a target at 100m with an M4 (due to its non floated barrel), how did I (and everyone else) hit the 300m targets during BCT so easily?

Marines hit at 500 if I'm not mistaken, which should be impossible according to this.

Quoted:


Under ideal conditions and minimal loading of force on the handguard you should see minimal deflection.

It's when you sandbag it with a load or sling it up tight that you should see significant deflection of point of aim.

Quoted:


The M4 with m855a1 is something like a 1.5-2.5moa gun.

The issue is forces exerted upon the rail is imparted to the barrel, which can shift point of impact 15moa.

So the gun will still shoot with decent groupings, they just won't be anywhere near where you are aiming.

Quoted:

This is an interesting question...

Im not sure, but I would assume greater, since the point of flex lets say whole barrel, would also effect the front iron(though disproportionately ),so irons group would be "less" effected by the flex since they somewhat compensate, but im just guessing... intersteing test. someone locate @Oldpainless

Quoted:
Lol OP thinks rifles and carbines do the killing.
Combined arms kills people and no one does that as well as we do.

Quoted:
thanks
@AR-180 what shift would you expect shooting the same setup with an AIMPOINT or ACOG on the receiver?

(honest question)

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15MOA change due to slinging or laying it across a barricade? That's absurd. Did you get that info from someone selling free floats?

Quoted:


No, just so we don't experience up to 15MOA in shift when using our rifles....You know, so soldiers can actually hit what they aim at.

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When are you going to be loading sandbags on top of the rifle, or slinging it up tight in combat? That seems like range conditions, which would be ideal conditions.

If they have time to get into those conditions, why couldn't they just replicate the conditions in which they're hitting targets at 500 meters?

Quoted:

You do know that they don't hit shit as it is. It takes something like 250,000 rounds of ammo to kill one bad guy.
Infantry tactics is spray and pray. When you are getting shot back at, you aren't taking time to aim. You are sending lead down range hoping it hits someone. It's purely a means of keeping enemies pinned down until air support shows up.

Quoted:


You can force the shift by pulling a VFG tight into your shoulder or using a barricade.

Read my link.

Quoted:

Hmmm

Maybe that has to do with the wide spread usage of receiver mounted optics and everyone being issued a non free floated rail.

When you can cause a point shift of 5-15moa by putting tension on the KAC RAS it's no wonder soldiers can't hit anything.

Quoted:


You must be joking.

You just have to be.

Quoted:


How so?

Sure PID is improved with modern optics, but POI shift is very real.

Let's say you pull the M4 tight into your shoulder, you line the ACOG up to the target....There is a huge chance you won't hit him if he is at 100M or beyond.

Because the KAC RAS will force pressure on the barrel and change the point of impact to something different from your ACOG.

Quoted:
Looks like the AK-12 will go to the general army soldiers while Spetznas will be getting the AEK-971.

Russia set to adopt both AK-12 and AEK-971.

Personally, it's interesting to see every country modernizing their general issue rifles except us.

The AK-12 features a free float barrel, which I believe this makes us the last first world country to employ a general issue rifle that still retains a non free floated barrel.

This means Russia will now have a general issue rifle capable of far better accuracy and consistancy than our M4A1s, that can see up to 5MOA in point of aim and point of impact shift by sling, barricade, or foregrip pressure when exerted on the non free floated KAC RAS.

We really need to modernize our general issue rifles as we are greatly falling behind in this category at this point.

The US at this point needs a M4A1+ program more than ever now.

Quoted:


How so?

Sure PID is improved with modern optics, but POI shift is very real.

Let's say you pull the M4 tight into your shoulder, you line the ACOG up to the target....There is a huge chance you won't hit him if he is at 100M or beyond.

Because the KAC RAS will force pressure on the barrel and change the point of impact to something different from your ACOG.

Quoted:
Looks like the AK-12 will go to the general army soldiers while Spetznas will be getting the AEK-971.

Russia set to adopt both AK-12 and AEK-971.

Personally, it's interesting to see every country modernizing their general issue rifles except us.

The AK-12 features a free float barrel, which I believe this makes us the last first world country to employ a general issue rifle that still retains a non free floated barrel.

This means Russia will now have a general issue rifle capable of far better accuracy and consistancy than our M4A1s, that can see up to 5MOA in point of aim and point of impact shift by sling, barricade, or foregrip pressure when exerted on the non free floated KAC RAS.

We really need to modernize our general issue rifles as we are greatly falling behind in this category at this point.

The US at this point needs a M4A1+ program more than ever now.

Quoted:


How so?

Sure PID is improved with modern optics, but POI shift is very real.

Let's say you pull the M4 tight into your shoulder, you line the ACOG up to the target....There is a huge chance you won't hit him if he is at 100M or beyond.

Because the KAC RAS will force pressure on the barrel and change the point of impact to something different from your ACOG.

Quoted:
Also here's a few links discussing it that I found in Google.

http://www.lightfighter.net/topic/ar-free-float-rails-and-impact-shift