it strikes me that a major flaw of .50cal is the poor hit probability, due to the rather harsh recoil and the lack of a heavily moving barrel on the M2

looking at 40cal sniper rounds, they are much smaller than .50 and with a CT or polymer case the weight savings would be drastic.

ive been thinking about a bullet which is 10.9mm approx.  (the 416 barrett  has a 10.5mm), and about 470grains.  (416 uses 420grains usually)

this would be combined with a CT case if possible, and a ME of just under 11, 000 ft lbs - creating much less recoil than .50

the weapon would be 10kg lighter than M2, and of course use a heavily recoiling barrel and suppressor.

any thoughts

I think the poor hit probability is down to low-quality barrels and bullets used 

A friend of mine is just chambering a .416Barrett from a barrel blank i got from Peurala in finland. 

But keep in mind 50BMG has host of bullets with payloads ,

smg762 said:

and the lack of a heavily moving barrel on the M2

???

The M2HB is lot "lacking a heavily moving barrel".

.50 BMG wasn't designed as a long-range precision cartridge. It was anti-tank and aircraft. Some "bulk" .50 isn't very accurate, and neither are the MGs.

Now, a properly built rifle, with properly made ammunition, is completely different. As in group size at 1,000 yards being the same as an M2 with service ammunition... at 100-200 yards.