I just now called A.R.M.S and ordered a SIR system #50 slimline bi-level ,I have asked this before - here goes . Will it fit on the old M4 type barrel from RRA that does not have the true contour ? It appears there will be enuff clearance , but I want to be sure I can always cancel I dont want to but I know somebody out there in AR land has the answer - please email me asap . Thanks -
Happy Thanksgiving - remember spit the little hard round things out .

Since the SIR mounts to the upper and the delta ring and free floats the barrel, the contour is irrelevant.

So it will work fine.

I figured as much but you know these things go , or maybe not I type of guy that if it didn't fit , give me a file ... whew kick me !    thanks bro