Hello folks,

I've finally attached a flash light to my home defense carbine. I'm using YHM non-free floating forend to attach the light and the grip.

I've noticed a few things while I rezeroed my carbine at 100 yards. Even when I moved the things around, the iron sight seemed to have adjusted itself in the general direction of the shift in zero. However, the optics mounted on receiver were significantly off each time I moved things around and had to be rezeroed.

I'm not sure if this was just a coincedence but it got me thinking. Was the iron sight less susceptible to non-free floating forend because it has its front sight tower attached to the barrel, therefore moving the whole thing at the same time?

The point of a freefloat tube is to isolate possible changes in the barrels point of impact by forces applied to the rail.  

So if you are going to use IRONs, the smartest thing to do is have the FSB mounted to the BBL as its POI will remain untouched.

You completely loose the value of a freefloat tube if you use IRONs that are mounted on the tube.  It is true, you do not change the POI of the barrel, but you change the line of sight which brings you back to the place you started with a non-floated barrel.

Modern red dots and optics are so reliable now, that Iron Sights are becoming a thing of the past.  Back up Iron sights are just that....back ups.  People would rather rail mount a front folding BUIS and get the advantages of clear line of sight without a front post in their optic, and do not want to sacrifice rail real estate with a FSB barrel attachment.

The best of both worlds from a purely practical standpoint is a folding barrel mounted BUIS.  Here is a pic of one such example.  This guy feels his irons and their uninterrupted line of sight is warrants this setup.  He is right.  But it is just so early 90's

Right, my front sight tower is still the stock one which is part of the barrel. For the time being, I'm using iron sights (with the carry handle and all) exclusively on this carbine.

So I guess this thing makes sense then.

Quoted: You completely loose the value of a freefloat tube if you use IRONs that are mounted on the tube.  It is true, you do not change the POI of the barrel, but you change the line of sight which brings you back to the place you started with a non-floated barrel.

Sorry, that's not even close to right.

The reason for using a free float tube is to isolate the barrel from sling or bipod forces, and from binding as it expands from sustained fire.  Nothing else.  Where the front sight is located is irrelevant.

Placing the front sight on the float tube does nothing to degrade accuracy.  So the line of sight is different.  So what?  Adjust the rear sight or front sight post to rezero and you are done.

Quoted: Was the iron sight less susceptible to non-free floating forend because it has its front sight tower attached to the barrel, therefore moving the whole thing at the same time?

It's possible.  But repeatability would depend on placing the same deflection on the barrel every time, be it from sling tension or from the force reaction up through a bipod, front rest, etc.  It's also possible that the true effect was maked by the greater shot to shot dispersion due to the lower level of aiming precision afforded by irons.

If you want ironclad repeatability, get a free float.