Back up iron sight on free float rail

[Kwanger]

Everyone always raves how important it is to have a free floating barrel for accuracy - usually achieved by a freefloating rail/forearm setup. I can see how this is the case when using a receiver mounted optic...but what about when using rail mounted back up iron sights?

I don't see much discussion on the issue, but surely if you are using a front back up iron mounted on, say, a freefloat rail, when you rest that rail on anything, or have a sling attatched to that rail and crank on it, the rail will move independently of the barrel (as designed).....but unfortunately, so will your front buis, and your zero will also therefore move, negating the effect of the freefloat forearm.

I am therefore thinking the best iron sight setup would be a freefloat rail, but front sight attatched to the barrel, not the rail, as this would give you the constant sight plane between receiver mounted rear and front sight. Is my thinking correct?

 

[wally]

The main improvements from free-floating comes from not having the fore end load the barrel barrel so POI doesn't shift with pressure from a sling or vertical loading when using sandbags or a bipod and by not having your grip or hold influence barrel harmonics.

On some guns fore end loading effects are really noticeable -- for example. on my Polytech M1A if I zero off sandbags POI will pull almost 1.5" left if I shoot using a "hasty sling".

As a general rule you'll get the best results with the longest sight radius when using iron sights.

 

[kwelz]

BUIS are just that Back ups. Your Optic is your main sighting device and is not affected by movement of the rail. BUIS will still get you on target even with the minimal flex you get from holding the rail.