Difference - air volume
The extended v2 has 19 tooth sector to give a longer piston stroke to create more air required for longer barrels
Though length doesn't equate to accuracy - but if you try and fit a 550mm+ barrel to a G&G SR25....
good luck getting the oomph required - even with a bore up cylinder
You can turn almost any decent normal M4 into a dmr without having to go down the must have SR25 route
most sites aren't that picky on proper DMR's as long as they are locked to semi
or go for cyma m14 - CM032 that seems to be a popular dmr gun
