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I don't know where this rabbits going but all rifles flex. Take any rifle, attach a bi-pod on it and shoot off the ground or bench. Vary your cheek weld pressure and watch your groups open up. Usually they will go higher due to flex. A free floated barrel is less affected but still affected.
Does it matter? No. How you deal with it does.
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Nature of the beast in other words? With this being the soul reason that AK's & mini 14's having thin barrels are the results of lack of consistent accuracy, it would then make sense that the proper sizing & profile of AR barrels, would make them less prone to the affects of flex. How thin is to thin? It's going to be a compromise regardless. Even then the AR is still accurate. Now with the AR being as accurate as it is to begin with, {even with standard HGs} it now focuses on how the FFT/Rs are mounted to the rifle & the strength of the way in witch it was made. The way the DDL rail attaches to the UR is pretty stout & on top of that, the profile it's self is inherently made more stiff. It all boils down to how the FFR/T attaches to the UR. You now have to make an educated decision as to how light you want to make your rifle. The lighter it is, the more prone it is to flex. IMHO anyway.
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Cesiumsponge already partially worked this out but: If you have a CompM2 that's a 4 MOA? red dot. The guys who actually practically tested this were getting deflections in the .01 of an inch range at most. 1 MOA at the muzzle of a 16" barrel is 32pi or about 100.531/21600(minutes in a circle) = 0.00465. So 4 MOA is about 0.0186 of deflection at the muzzle of a 16" bbl.
So for a carbine it's minimal, but possibly notable. It could affect BUISs attached the the very front of a free float rail a lot though.
(My math may be wrong, but Im fairly sure of the theory.)
Last edited by ZRH; 03-02-11 at 04:31.
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This is a really interesting thread since I expected there to be some POA change when the front sight is mounted to a floating handguard. But it is not as bad as I expected for a working rifle application.
So I took Cesiumsponge's measurements and plugged it into a spreadsheet and here is what I got:
Sight radius: 18"
Elevation POA change
Off hand support: 0.5 MOA
Sling: 0.5 MOA (2 MOA windage change)
Bipod: 1.3 MOA
The interesting thing to me is that the POA change using a bipod is larger than off hand. So if I zero the rifle on the bench or bipod, my POA would actually be low if I switch to off hand or sling. 0.8" high at 100 yds is really not a big deal and even 2.4" at 300 yds is well within man size target. It does get a little less acceptable pass 300 yds but that depends on application. In the end, a 2 MOA working rifle might be closer to 3 MOA depending on how you hold it.
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Didnt see this posted, here's a slow-mo vid of the AR15 barrel whip when free-floated, both heavy and pencil suffer:
http://www.youtube.com/watch?v=0Xr_RG_lcNk
Last edited by albatrossarmament; 09-10-13 at 19:40.
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