I understand that there are 2 different front sight bases out, one for A2 rifles and one for Flat tops (F Marked)

Is the LMT designed to work better with the A2 or the "F" Marked.

Specifically I have 2 identical uppers.  One is F marked and one is not.  
I also have 2 different BUIS sights, one is the LMT, the other is a ARMS 40L-SP

What I want to know is if one sight will work better on one upper, or is it a wash?

Thanks for your time.

FWIW, I use an LMT BUIS on my M4.  It has a standard, non-"F" FSB and I needed the 0.040" taller front sight post to sight it in properly.

F marked are carbine FSB
non F is rifle length FSB

You need a taller FSB when you put the FSB closer than the rifle position.  Simple geometry dictates this.  I hope you can see how the line of sight is higher closer to the rear sight and why this is.

Some companies go cheap and use rifle FSB on carbine which is of course too short.

Troy works with propper height FSB relative to placement distance from rear sight.  Therefore it works with both if they are used in the correct location.

The taller front sight must be used with impropper FSB on carbines and often the post sticks up higher than the ears of the FSB.

This truth is the same for all AR15 type rifles and all BUIS.  Dont know of anyone making the BUIS improper height to work with A2 FSB on M4 legth gas system.  This would also make the A2 FSB too tall if such a BUIS was used on a 20" rifle with rifle positioned FSB so it makes no sense to do this.

Hope this gives you a better understanding of why the correct FSB height is used and why BUIS are set up to be correct height.

+1 on what DevL said.






but i have to admit the taller front sight post has been hit and miss with me. same manufactor buis on various bushmaster's have yielded different end needs.

So basically all BUIS and A3 carry handle rear sights should be approx the same height regaurdless of manufacturer (assuming it's in spec)

For my case then, I will need a taller front sight post to go with my non-F marked front sight, regardless of which BUIS I use?


Thanks!

I have had it work both ways. On one gun I needed the taller sigth post, on the other I did not. With the LMT I needed it.

Just order a couple of them next time you order parts. They're pretty cheap and its always worth having a spare.

The variance is close enough you may not need it but expect to need it with any rear sight... they are all the same height. (rear BUIS)

Personally, I think that the type of hold you use with the front sight (lollipop, Army, USMC, etc.)and each individual's "centering" of the front sight post in the rear aperture plays heavily into whether or not you need a taller front sight post.  If it was cut and dried mechanical differences, you would see more consistency, but it's not and the largest variable is the shooter.

But then along comes Lancelot, and he blows my theory completely out of the water.

I still believe the shooter is a large variable and is the reason for the hit and miss on this issue.  YMMV.

Quoted: Personally, I think that the type of hold you use with the front sight (lollipop, Army, USMC, etc.)and each individual's "centering" of the front sight post in the rear aperture plays heavily into whether or not you need a taller front sight post.  If it was cut and dried mechanical differences, you would see more consistency, but it's not and the largest variable is the shooter. But then along comes Lancelot, and he blows my theory completely out of the water. I still believe the shooter is a large variable and is the reason for the hit and miss on this issue.  YMMV.

But I never said I could hit anything with it....

I agree with your theory. And everyone holds the gun differently, and different stocks make for different cheek welds and thus, theoretically, different sight pictures I suppose.

My eyes are different then yours, and so our sight pictures will be slightly different. That's why you always sight in your own gun, (don't let anyone do it for you)