Free Float Rail Alignment (potential problem?)

[Dunderway]

First off a disclaimer: This is a high quality upper and a high quality rail from very respected companies on this forum. As per forum rules, I will not name them at this time, but will make contact if I have an actual problem and am not just being anal.

I just installed (3 times) a two piece style clamp on rail which utilizes the stock barrel nut to a standard M4 carbine.

Through all of my attemps at installation, the rail has been off center in conjunction to the FSB. Not a lot but a noticeable amount (1/8" or so when looking at the FSB/bayo lug). I basically want to know if there is enough variance in forged FSBs and barrel nuts to make this knit picking, or is it an out of spec part? FSB is not canted, the rail has a larger verticle gap on one side of the FSB than the other, both top and bottom.

It really seems to pose zero problems aside from my OCD, but I have spent enough money on this to have it be right. I'm also 100% positive that any of the mfgs chosen will do so if needed.

Thanks in advance.

[Iraqgunz]

Have you considered posting pics? Is it remotely possible that you are doing something wrong?

No company is above screwing up. It's what they do about it, that sets them apart from others.

[C4IGrant]

Sorry, I am missing something. Are you trying center the rail with the FSB?? If so, why? You align it with the receiver rail and nothing else.


C4

[rob_s]

Interpolating here, but is this a 7.0 rail on a carbine-length gas or a 9.0 rail on a mid-length gas, or a 12.0 rail on a rifle-length gas?

Also, is the top rail of the handguard perfectly flat with the flattop upper? In other words, if you set the entire assembly on a table upside down does every rail section touch the table?

[Dunderway]

Have you considered posting pics? Is it remotely possible that you are doing something wrong?


It is very possible, and probably likely. I actually just wanted to make sure I was doing it right before I posted pics and brought names into it.


Sorry, I am missing something. Are you trying center the rail with the FSB?? If so, why? You align it with the receiver rail and nothing else.


I have it centered with the upper, but the rail seems very off center at the muzzle end. I assumed that if my upper, barrel, and rail were all straight then I wouldn't be seeing this, but I could very well be wrong.



Interpolating here, but is this a 7.0 rail on a carbine-length gas or a 9.0 rail on a mid-length gas, or a 12.0 rail on a rifle-length gas?

Also, is the top rail of the handguard perfectly flat with the flattop upper? In other words, if you set the entire assembly on a table upside down does every rail section touch the table?

This is a 7" FSP rail. I noticed that after the first installation attemp the rail was actually touching the bayonet lug on one side. That time I did it incorrectly I believe, by tightening onto the barrel nut before tightening the bolts that actually hold the two peices of the rail together. It's better now, but still off a little to one side.

[C4IGrant]

If the rail is square with the receiver, then drive on. If you are concerned that the FSB is canted, zero the gun with your irons. See how many windage clicks you get. If it is more than 11, it is out of spec.


C4

[Dunderway]

Aimpoint was zero'd with very little adjustment and the BUIS (yet to be zero'd) is barely off the dot when fully centered. I'm very happy with this setup, but just wanted to make sure I didn't have a problem or that there wasn't a trick to the install of this type of rail due to my inexperience.

FSB also didn't seem canted because the rail was equally off (top and bottom) to one side of the FSB, not diagonally (clocked), which I assume would be the case if a canted FSB was suspect.

I'll forget it and drive on, unless any other suggestions are made.

Thanks,