I ordered this for my Armalite SPR. When I went to install I noticed that the screws did not have plastic square inserts over them to allow them to be flush with the rail walls, thus making the sight stable. I went ahead and tried it and just as I suspected there is play in the sight (back and forth). Were the inserts supposed to be with the sight? Am I supposed to order them seperately? Is it only designed for the 3-rail gas block in the catalog (if so that should be stated). What gives?

I dont think that the sight is supposed to come with plastic inserts. What makes you believe that they do? I cant say I know everyhing about this particular flip up fron sight, but if it is made to fit milspec rails, and the rails on your armalite gas tube are milspec rails, they should work together.

Just to be sure, maybe try to mount the BM front sight to one of the flat top rails. They should be in spec. If the front sight does not secure to that rail, there is probably something wrong going on with the sight. If it does fit, then something is probably wrong with the front sight rail on your barrel.

BTW, all of this is purely guess work. I have never seen the Bushmaster flip up front sight you are talking about in person, but looked at it on their www site. Sorry I could not be of more help?

It fits just fine, it's the movement that bothers me. Okay the distance between the rails (on the rifle) is say a quarter of an inch maybe a little more. The screws are say half that width. So without any inserts there will be say 3 or 4 centimeters of play back and forth on the rail. Not side to side, back and forth on the rail towards the front of the barrel and back towards the reciever. This is the movement I can't make stop unless there is an insert of some kind. Or that it is supposed to move like that?

No, it certainly isnt supposed to move, but I dont believe it is the cross section screws that should be clamping it into place either. Some mounts dont even use screws or the cross sections of the rails to secure themselves to the rail. The removable carry handle and ARMS throw lever mounts are examples of this.

This might sound like a realy dumb question, but are you tightening the screws enough? If not, crank down on them and see if that works. Once tight, the thing should be solid. If you are cranking down on them and there is movement in the mount, you have a problem somewhere.

Mu BM risers have the plastic block sleeve,but my bmas flip up sight does not.

Yes I have cranked down on the screws very hard, all most more than I dared. The problem there is that they are a solid piece of aluminum. My Arms#40 flip rear sight is a two piece system along with the plastic insert, which makes total sense. It says right there in the catalog though that it is designed to fit snugly on the rail with allen screws. So I guess I'll mess with it again. What I really need to do is speak with either bushmaster or someone who has one of these.

I've got a factory-installed BMAS flip-up on their three-rail gas block.  There is no sign of inserts, just the two mounting screws.  The sight does not move on the rail.  Considering the amount of heat at the gas block, I'd think any plastic shim would melt very quickly.

IMHO, I'd say you need to 'pre-tighten' the sight base so it's an interference fit before you try to slide it on the rail.  This way you're not using small fine thread bolts to 'bend' the sight base.  I can send you a front picture of my rifle - send me your emailAddress. It shows how the factory-cut groove under the upper right edge of the sight base appears narrowed, tightening the sight to the rail.  It seems you've checked the rail to see if it's in spec, so the above is my recommendation for the next step.

fyi

I certainly could be wrong but it seems like in my search for a flip up front sight for my Armalites I heard/read that the Bushmaster will only work on their 3 rail block,not on Armalites.Armalites are supposed to be mil spec so does this mean the bushmaster is not?

The subject of front flip ups has been visited several times in the past few months.Unfortounately about all I got out of it was the GG&G was the best because it "costs more".With all the flattop Armalites out there I can't believe we don't have more choices for our flattops.