I was looking at a picture of the LMT MARS-L as adopted by New Zealand and I was remembering how not that long ago I read all sorts of people saying that the future of the AR was going to be monolithic uppers.
Greater rigidity, accuracy & precision, no top rail gap interfering with optics mounting, simpler and less parts, and all manner of other improvements were the reasons why the monolithic upper was the future.
I tended to point out that if the handguard got damaged, then you had to replace a whole larger more expensive assembly. Don’t get me wrong, I like monolithic uppers and I own a few.
For example this Colt LE6945 pictured has a monolithic upper.
So what was it we were suppose to have by now?
There was going to be this M16A4 Product Improved(Sometimes referred to as M16A5). This was going to be the USMC new rifle which would be a collapsing stock(Some sources said VLTOR A5, others Magpul UBR) and a VLTOR monolithic upper. It might have looked something like this:
The USMC ended up moving to the M4 and the M27 IAR. We don’t know how seriously the Corps ever really considered the Product Improved M16A4. But that didn’t stop rampant speculation by gun nuts.
Anyways I think that the ultimate customization available to the AR is what killed interest in the monolithic upper. For example some years back Noveske barrels were extremely popular on high dollar custom AR15s. The more popular monolithic uppers like the LMT MRP used proprietary barrels and so people couldn’t use what ever is the flavor the week. Similarly preferences in handguards changed. We went from people wanted a M4 barrel with KAC RAS, to a long free float quad rail, to long slick tubes. Now MLOK and Keymod are everywhere(but it looks like MLOK is winning). Someone who bought an expensive monolithic upper is locked into their choice.
I think the monolithic upper has lost out in the AR market, but I expect most any new competitor to the AR15 will likely have a monolithic upper with perhaps something like a removable or interchangeable side/bottom section.