Other folks have posted numbers for variation in gas block/rear sight base width/rsb pin hole size, etc.
I have compared the two 858s I own. The gas block is slightly different on both. On one the top rear "lip" where the piston slides has a slight flare. On this rifle the rail fits very snugly. I have to press the rear of the rail into place to put the pin in. There's no noticeable movement at all. On the other rifle the rail drops right in. This one has very slight movement vertically at the gas block and rear sight base.
I expect that NEA will be able to refine the design to accommodate these individual variations.
I have compared the two 858s I own. The gas block is slightly different on both. On one the top rear "lip" where the piston slides has a slight flare. On this rifle the rail fits very snugly. I have to press the rear of the rail into place to put the pin in. There's no noticeable movement at all. On the other rifle the rail drops right in. This one has very slight movement vertically at the gas block and rear sight base.
I expect that NEA will be able to refine the design to accommodate these individual variations.


















































