Lol. Ok.
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I'm not Rifleman, or speaking for him but...
Sights mounted to a free float handguard/rail simply cannot be as precise as sights attached to the barrel. If they are used as short range BUIS, the precision should be adequate and certainly better than point shooting.
Andy
I’m saying irons do belong on FF rail guns but solidly affixed to the barrel. I’m a fan of the Centurion cutout rails for that reason. I’ve seen point of impact shift issues with BCM, Centurion and Geissele rails running buis attached to the rails when the guns are used in other than flat range conditions.
There's a bit of nuance about projectile weight and velocity that affects it - 36yd is preferable for 300m/yd if we're talking 20" barrel 62gr, and it's nice that we can abuse a BDC reticle that allows for quicker/easier 50M verification.
As far as barrel deflection versus FF handguard deflection, the answer is that barrel mounted will chase some of the imparted loads in various positions, it's as simple as that. Those deviations are all <2moa in the grand scheme of things, and if you can shoot ~5 MOA for an overall probability distribution, you are an Expert marksman by jarhead standards.
It's not ideal, but I haven't noticed a meaningful difference in spread between my FF railed DD fronts and Centurion FSP setups. The best end-run around that is primarily using an optic, which negates most of those issues.
The important way to think of it is that optics are just affixed to a receiver that doesn't chase those deflections, so any deviation between FF handguard deflection and what the relative barrel deflection would be at the FSP are still appropriately referenced against what an optic mounted to the upper would be.
So... short answer is that any differential is completely in the noise compared to how terrible human physiology as an artillery platform realistically is, even under ideal circumstances.
I use a DD rear with standard front sight/gas block. My zero is 36 yards and the front post is nearly bottomed out, works for me. The ears for the front sight do a good job of protecting the KNS pin head front I use.