It seems they are discussing something similar in this thread... http://www.ar15.com/forums/t_3_118/556326_As_a_mount_for_a_front_sight__how_reliable_stable_are_free_float_rails_.html

If there is deflection in FF rails and none in the barrel when shooting from the prescribed prone supported position, then the point of impact/aim will still be off.  It's better off having a front sight based on the barrel than the FF rail IMO.

AMUshooter,

Excellent post with excellent presentation.

My share. I always zero my weapons from that stance, which I'm shooting most. That means magazine support for longer ranges. When I shoot kneeling or standing, I shoot to the shorter ranges and the POI difference doesn't matter so much. I adapt to the situation and if necessary, change my POA to gain the right POI.

Friend of mine always zeroed his .223 CZ bolt action hunting rifle from the bechrest bech because that "is the most stable rest found from the shooting range". And when he got hunting birds, he was shooting with bipods from prone position or without bipods from backpack rest. And shooting birds is that kind of sports, where few centimeters mean a lot. Every time, he found that his POI was different than his POA when he got out to the forests, and was caught thinking that were there something wrong with his rifle, scope or ammo, compared to the last shooting range trip. I said no, you just shoot from different position and from different rest than you zero your rifle.

I'm going to go out on a limb here and say that the difference is more about head/eye position than rifle support. I'm assuming that barrel support and head position (given the increased height of the body on the final stage) is the cause for the increase in elevation on the final group.

Thank you for the next couple videos. Those certainly rounded out your test well.
As far as the position thing, I was just meaning that you could use a 20rd mag for the barrel rest part and use a block that would hold it at the same level as your mag-rest portion. This would keep the rifle in the same position relative to your body. I think that this is probably a non-issue as your follow-up videos were much closer to this, with the new block used.
As for the barrel nut pressure, I agree that there certainly is an effect caused by this, but what I meant is that the pressure applied when using a standard non-free-float handguard, isn't pressuing the BN in the same way. The HG is merely putting pressure on the underside of the BN but not twisting on it with any leverage, as a BN mounted handguard would be.

What is so hard to understand about when you flex the barrel one direction, that's the way the bullets spit out?
Its not how he was looking through the scope, its how the barrel was bent.

I would like to see him try it with an iron sighted rifle like a 20" A2 and see if it still has as much effect on throwing the bullets.

Never thought of that. It shouldn't be nearly as great a change, because the barrel mounted front sight would rise at the same rate as the barrel, but the rear sight isn't mounted at the rear of the barrel, rather the rear of the upper, so that would cause a discrepancy between the barrel and irons alignment. Certainly would be interesting to compare.

You BASTARDS!   Alright, consider it done.  Your just lucky I have one of those.  

My rifle is free floated but the front sight is still on the barrel.  I imagine at 50 yds there will be minimal POI change.  (at least its sunny today)

P.S.  Armed Pete, Pony up that OBR so I can test that.  I will put it up against the LR8 and the Scar.  I think I might be able to actually break the SCARs little barrel if I put too much pressure on it though.  LOL

I have a A4 you could use a carry handle on.

And are you in need of the SCAR?

kkuo,
I agree.  

And as for the SCAR I told myself I was not going to ever shoot one again so I will pass. LOL Thanks though.  
I am still sore from shooting mine last year  

A standard free-float will eliminate most of the stresses placed on the barrel, resulting in a much more accurate rifle. Most shooters won't see any difference in accuracy between a FF and  monolithic upper receiver/forend.

A monolithic upper receiver has much the same effect as a free-floated bolt action.

You pretty much eliminate stresses placed directly on the barrel, but there will be an ever-so slight change in pressure transmitted to the barrel through the receiver from the forend. For maximum consistency you want a rigid stock (or forend) and a receiver with a rock-solid bedding into the stock (not a problem with ARs).

This video for the Savage Accustock does a pretty good job of explaining what makes bolt-action bedding good.
http://www.savagearms.com/accuracy/accustock/

Now imagine the similarities and differences between that and a monolithic AR upper: Rigid forend? Check. Barrel freefloated? Check.  Receiver solidly bedded into the stock? Not an issue.

An extremely accurate bolt-action rifle (such as a Surgeon or AI) will be more accurate than any AR, but at that point it's mostly (IMO) because of the increased rigidity of the steel receiver over an aluminum AR receiver. Keep in mind that at this point we're talking about differences in accuracy outside the abilities of the vast majority of shooters.

Thanks for the post, OP!

Updated w/ new test. 18 dec. 2011
Rifle is a RRA NM A2 using iron sights @ 50yds. (its fun to shoot a hammer @ 50yds. LOL good for the ego)

As long as their iron sight setup is optimal.  In other words, their front sight post is based on the barrel and it is not a BUIS mounted to the FF rail.

I think an iron sight mounted to the rails of a monolithic platform is okay though.  Not perfect, but the deflection should be very minimal.

If I read the test results correctly, this config saw the least variance from the different positions. I think it didn't even have a free floated handguard. Does this mean standard mounted handguards will be more consistent with varying shooting positions? I really expected the barrel supported shots to be higher based on the previous tests.

NM A2 has a free floated handguard.  

It just has the external appearance of standard, non-FF handguards to abide by Service Rifle [National Match] rules.  It's a free float tube with handguard shells attached to the outside.  

~Augee

Damn, those are nice groups. This is even more consistent than I had expected. Great job, AMUshooter10, you sir, have done an excellent job here.
Thank you.

Yup its free floated just like Augee said.  

I too thought there would be more Point of Impact change when I rested it on the barrel.  

But the Front sight is hooked on the barrel and the barrel is pretty thick under the tube.  (And wrapped in led...19lbs)

I really need a set of new handguards, I am just superstitious about the ones on it now.  Even though it looks like ass.

Funny how the A2 did the best.
I guess that's what I expected since the front sight is on the barrel and flexes with it.
Very good info and pictures/videos.

Thanks guys!  I appreciate the feedback.

It only took 30 mins to do the shooting, but I think I spent half my life waiting for the videos to upload

In all fairness that A2 did all the work on that last one.

That gun is a hammer!