Free float handguard vs non free float: a few questions

[Wondering Beard]

I understand that a free float handguard can enhance the user's accuracy (not the accuracy of the rifle itself) because it doesn't contact the barrel and thus doesn't affect it when shooting.

So it is safe to assume that whatever pressure the shooter applies on the free floated hanguard, be it by tightening the sling or resting it on something or even by adding and/or replacing accessories mounted on the handguard, the rifle will always shoot to where it was originally sighted.

However, in the days before all the free floating rails, I believe the Marine Corps was training its guys to make hits a distances of at least 300 yards (I don't know what the basic skill requirements are for a new Marine). As a result, I'm starting to think that the advantages of the free floating rail may not be as great as claimed.

Thus my questions:

More or less how much pressure needs to be put on the rail to get a significant shift in POI. I don't need numbers but, for example woukl resting it against the side of a barricade, the way we see competitive shooters do, make a significant change and by how much would that be? would resting it on sandbags or even just using the magazine as a monopod while prone create the same problems? less?

If the shift is significant, is it predictable? in other words, if using the barricade method described above, can I just change my POA by x inches (assuming I already know what the shift is going to be) to compensate for the expected shift? or is the shift not that easily calculatable?

In a combat situations, has the use of cover to rest the rifle been known to create problems? if not, why not?

These questions are not about rifles whose main purpose is to make tiny groupss at long dstances. I'm talking about carbines that one would use to defend oneself and while I know that a defensive shot with a carbine is likely to never be beyond 100 yards, it would be good to know that a 300 yard shot could still be made, while using cover with a rifle whose handguard doesn't free float.

[rob_s]

This is the second time on the second forum in two weeks that this subject has come up, and it has inspired me to attempt to quantify the answer with a couple of rails and handguards.

[oregonshooter]

My money is on "no significant difference" for combat accuracy. Let us know what you find Rob.
A standard M4 with non-floating hand guards will make COM hits at 650yards all day off a rock, bag, or cross sticks, IME. What more do you need?

[Paulo_Santos]

With a Non-FreeFloat Handguard, the front sight is mounted on the barrel, so the shift will be practically nil when using a sling or leaning it on something. Where you will have the shift with the Non-FreeFloat handguards is when you use an optic and you put pressure on the barrel by using a sling or leaning it on something. From 0-100 yards the shift will be minimal at best, unless you crank on the sling for whatever reason.

With a Free-Float Handguard, the only time you will have a shift is when you mount a front BUIS on the Rail.

[thatdamngoat]

However, in the days before all the free floating rails, I believe the Marine Corps was training its guys to make hits a distances of at least 300 yards (I don't know what the basic skill requirements are for a new Marine). As a result, I'm starting to think that the advantages of the free floating rail may not be as great as claimed.

The Marine Corps qual consists of shooting different stages at 200, 300, and 500.

[Wondering Beard]

With a Non-FreeFloat Handguard, the front sight is mounted on the barrel, so the shift will be practically nil when using a sling or leaning it on something. Where you will have the shift with the Non-FreeFloat handguards is when you use an optic and you put pressure on the barrel by using a sling or leaning it on something. From 0-100 yards the shift will be minimal at best, unless you crank on the sling for whatever reason.

With a Free-Float Handguard, the only time you will have a shift is when you mount a front BUIS on the Rail.

Just to make sure I understand:

when using irons only with an FSB and a non free float handguard, if pressure is put on the barrel the front sight itself will move and still get aligned by the shooter through the rear sight, thus no or little shift.

When using an optic on a non free float handguard, the barrel may be moved due to pressure but the optic, set on the receiver, won't be, resulting in shift.

Adding or changing a front BUIS, or just changing accessories on a free floated handguard will change the pressure on the handguard possibly causing it to move while the barrel won't and thus we get a shift.

Did I get it right?



This is the second time on the second forum in two weeks that this subject has come up, and it has inspired me to attempt to quantify the answer with a couple of rails and handguards.

That would be great!



The Marine Corps qual consists of shooting different stages at 200, 300, and 500.

That should turn out shooters who have a good understanding of marksmanship. I'm certainly not capable, for the time being, to reliably get hits at 300 yards never mind 500! Then again, I'm no rifleman.

[Paulo_Santos]

Just to make sure I understand:

when using irons only with an FSB and a non free float handguard, if pressure is put on the barrel the front sight itself will move and still get aligned by the shooter through the rear sight, thus no or little shift.
CORRECT

When using an optic on a non free float handguard, the barrel may be moved due to pressure but the optic, set on the receiver, won't be, resulting in shift.
INCORRECT. THIS WILL CAUSE A SHIFT.

Adding or changing a front BUIS, or just changing accessories on a free floated handguard will change the pressure on the handguard possibly causing it to move while the barrel won't and thus we get a shift.
WITH A FREE FLOAT HANDGUARD, IF YOU HAVE AN OPTIC ON THE UPPER RECEIVER, YOU CAN FLEX THE HANDGUARD AND IT WON'T MATTER. WITH A FREE FLOAT HANDGUARD AND IRON SIGHTS ON THE BARREL, YOU CAN FLEX THE HANDGUARD AND IT WON'T AFFECT THE POI. WITH A FREE FLOAT HANDGUARD AND THE FRONT BUIS MOUNTED ON TOP OF THE FF HANDGUARD, IF YOU FLEX THE HANDGUARD,YOU WILL CHANGE THE POI.

Did I get it right?

Answers above.

[wareagle700]

Free floating a barrel is not just about correcting/helping shooter error. It does make the rifle itself capable of better accuracy. It has to do with how the barrel vibrates from shot to shot. Even if you assume there is no human error, in general, a free floated barrel will still be more accurate than a non free floated barrel. Thats why nearly every precision rifle has a floating barrel, iron sights or not. Whether you will notice the change in accuracy depends on the rifle and how you are shooting it.
ETA: I am not talking about shift or "combat accuracy". This is about free floating and accuracy in general for the OP.

[Wondering Beard]

When using an optic on a non free float handguard, the barrel may be moved due to pressure but the optic, set on the receiver, won't be, resulting in shift.
INCORRECT. THIS WILL CAUSE A SHIFT.
I did mean that it would cause a shift because the optic wouldn't be moved while the barrel would.

Adding or changing a front BUIS, or just changing accessories on a free floated handguard will change the pressure on the handguard possibly causing it to move while the barrel won't and thus we get a shift.
WITH A FREE FLOAT HANDGUARD, IF YOU HAVE AN OPTIC ON THE UPPER RECEIVER, YOU CAN FLEX THE HANDGUARD AND IT WON'T MATTER. WITH A FREE FLOAT HANDGUARD AND IRON SIGHTS ON THE BARREL, YOU CAN FLEX THE HANDGUARD AND IT WON'T AFFECT THE POI. WITH A FREE FLOAT HANDGUARD AND THE FRONT BUIS MOUNTED ON TOP OF THE FF HANDGUARD, IF YOU FLEX THE HANDGUARD,YOU WILL CHANGE THE POI.
Ah, yes. I should have differenciated between optic on the receiver, irons on the barrel and irons on the handguard


Answers above.
Responses in color

Thanks, my understanding is now clearer.

[pezboy]

With a Non-FreeFloat Handguard, the front sight is mounted on the barrel, so the shift will be practically nil when using a sling or leaning it on something. Where you will have the shift with the Non-FreeFloat handguards is when you use an optic and you put pressure on the barrel by using a sling or leaning it on something. From 0-100 yards the shift will be minimal at best, unless you crank on the sling for whatever reason.

With a Free-Float Handguard, the only time you will have a shift is when you mount a front BUIS on the Rail.

I wouldn't say that having a barrel mounted front sight makes the POI shift proctically nil. When changing from off hand to slinging up tight to supported with non free floated skinny barrel AR15s and skinny barrel M14s, there is definitely a significant POI change. There is a lot going on there other than changing the direction the barrel is pointing. Whether or not the shift on a persons weapon from one position to another is significant in a match/personal defense/combat situation is for them to find out.
Dustin.

[Paulo_Santos]

I wouldn't say that having a barrel mounted front sight makes the POI shift proctically nil. When changing from off hand to slinging up tight to supported with non free floated skinny barrel AR15s and skinny barrel M14s, there is definitely a significant POI change. There is a lot going on there other than changing the direction the barrel is pointing. Whether or not the shift on a persons weapon from one position to another is significant in a match/personal defense/combat situation is for them to find out.
Dustin.

Definitely the skinnier the barrel, the worse it will be, but for most combat shooting, it will not make you miss the target from 0-100 yards unless you crank the crap out of the sling. Now if you are shooting for pure accuracy, then I'd say it will matter.

[wolf_walker]

"free float" has been such a catch phrase for so long, but I don't think hardly anyone understand why or exactly what it does other than "increases accuracy", which no doubt it does.
I eagerly await some back to back testing from the man in the yellow visor. And my money is on very little difference for a "working gun" as the OP defines it.

[Stickman]

"free float" has been such a catch phrase for so long, but I don't think hardly anyone understand why or exactly what it does other than "increases accuracy", which no doubt it does.



Its very straight forward, and there is no mystery to it. A FF barrel is NOT more accurate, it simply is allowed to be free of the typical external influences that rob accuracy.

Think of it this way. If you take a tape measure, you can get an measurement. Take that same tape, and allow it to bend, and your measurement has changed.

[Aragorn]

Its very straight forward, and there is no mystery to it. A FF barrel is NOT more accurate, it simply is allowed to be free of the typical external influences that rob accuracy.

That is probably the simplest, and most accurate way one could put it.

[wolf_walker]

Its very straight forward, and there is no mystery to it. A FF barrel is NOT more accurate, it simply is allowed to be free of the typical external influences that rob accuracy.

Think of it this way. If you take a tape measure, you can get a measurement. Take that same tape, and allow it to bend, and your measurement has changed.

I was thinking along the lines of understand complex harmonics of the barrel from weight at different points along it's length and stress upon it in differing points effecting accuracy.
I'm aware of the existence of such things but that's as far as my knowledge goes, not really my bag. We all know it's "better" and in the most simple and practical terms why(good analogy with the tape measure), but there is always more to it.