1). Besides dimensionality changes, are there any real differences between the M4 and the venerable M16?
M4 has a shorter barrel, and a shorter, adjustable stock. The M16 has a longer barrel and a fixed stock.
2). For a time it seemed like many had a front handle/grip on their rifles – but that ‘fashion’ seems to have gone away, why is that?
(Those folks not using a front grip are simply grasping the rifle around the front rails)
Is there a compelling reason for this? or is it just personal preference?
The vertical foregrip is perhaps most useful on a full automatic weapon. Some even have bipods hidden inside of them. But they are heavy and can snag on gear when carrying. ARs are Men's Barbies, and are easy to accessorize with foregrips, flashlights, lasers, optics, buttstocks, railed forearms, etc. So you'll see a lot of stuff on an AR that isn't necessarily as useful as it is fun.
