AR15 quad rail and optics question

[walter34payton2002]

Hey guys, this is my first post here. I have a question regarding my AR 15 setup (DPMS 5.56, 16 inch barrel, m4 style). I have a Troy quad rail that uses the exiting delta ring and has the 2 parts that bolt into each other. It is very solid and I can't detect any movement. I have a Tapco vertical foregrip, ATN Javelin tactical light and a bipod on the rail. I just recently upgraded to the EOTech 512, EOTech 4x magnifier with flip to side mount, and the Magpul rear BUIS. I want to fit it all on the rail, but I am guessing that all won't fit and I am going to have to drop the 512 partially on the Troy quad rail (magnifier still in mail from Optics Planet). My question it this: Will dropping the Eotech partially on the Troy rail throw off the zeroing of the scope at all? I don't mean as in moving an already zeroed scope. I mean as in movement from the rail or will the fact that it is mostly on the flat top rail the EOTech can't really move even if it is partially on the Troy rail. As I understand it you need a free float to ensure it will have no movement or is this incorrect? Like I say, I cannot detect any movement as Troy is very, very good. However, I will need to know as much as possible.

 

[walter34payton2002]

I got everything and mounted it all up. The eotech 512 is just one notch barely touching the Troy quad rail. If no one has an opinion here then I think I will just have to fire hundreds of rounds and make sure she holds zero.

 

[taliv]

sorry, i have no experience with the troy rail. heard good things about them. shooting it is probably not what will cause it to change. banging it around in the back of your truck, slamming it into barricades and jerking on the foregrip are what will cause it to move around. possibly also temperatures, which could come with firing, but if black, will prob come with just leaving it sitting in the sun

 

[Z-Michigan]

I have an EOTech 552 bridging from receiver to a much cheaper quadrail (but still solidly in place) in the same fashion you describe. I have not found any problems of movement or zero changes.

It is always recommended that you not have ANY optic bridging from receiver top to a quadrail, as there is the possibility of rail movement. This is true even with free-float rails from the most expensive companies (Daniel Defense, etc.). But it's more of a recommendation than a requirement. While I wouldn't bridge the gap with a high magnification scope on a varmint or F-class gun, I expect you will not find any noticeable zero movement with the setup you describe, except if the quadrail comes completely loose and starts moving visibly - which is not likely if you install it right (very simple to do, no skill required). Movement of that type quadrail is only possible if you either don't tighten the screws holding the two halves together, OR if your barrel nut comes loose - in which case you have more serious problems.