Been reading and researching for a railed handguard purchase.

Have a KAC RAS on the way that I had hope would let me push my EOTech 512 more forward. It seems I have a upper with a higher rail height and the RAS will sit a bit lower than the receiver rail.

I'm learning that all recievers are not the same height. I have measured rail height differences on two rifles, one a DPMS and the other a Knights. The difference is .031"or 1/32". Doesn't seem like much but it could be.

With a higher reciever the use of a optic that transitions the gap could have a problem and a setup like the KAC RAS II or SIR would bind and at some point could damage the upper or handguard.

Anyone know why and how this difference came about. How do the manufactors explan the difference?

The KAC is to spec, the DPMS is not!
Jack

I truly don't understand why ALL manufacturers don't follow spec when many systems require it.  Odd if you ask me but I am sure it's a cost issue!

The others prob don't have to conform to specs because they don't sell to the government so they don't care, KAC, ARMS and the like do.  Just guessing.

Are RRA A4 uppers to spec?

I believe they are now.  I heard they picked up a government contract to one of the ferderal agencies.

My DPMS A3 upper rails are not to spec.  They are about 1/16" too high.  I compared it to a couple of other uppers, and its visibly higher.  I always thought DPMS was a good company, but after this and the fact that their customer service stinks (the upper had an off center FSB, and they told me that if I sent it back to them, they would "be happy to quote me a price"...uh, no thanks), I don't think I'll buy another.  

Ghost

Is it one of their extruded uppers? They have a note somewhere saying they are a little taller (I think).