http://media.militaryphotos.net/photos/M4-Carbine/carbine07 http://www.fas.org/man/dod-101/sys/land/m16.htm The above _link_s show the M4 carbine. I've always wondered what the 'step' in the barrel just forward of the front sight is for. On the F.A.S site's pictures it shows a M4 with m203 grenade launcher, the launcher seems to clip on just where the 'step' in the barrel is. IIRC M16s mount the M203 without the 'step' in the barrel so why is it needed on the M4? Jeremy Thomson

#http://media.militaryphotos.net/photos/M4-Carbine/carbine07 #http://www.fas.org/man/dod-101/sys/land/m16.htm # #The above _link_s show the M4 carbine. I've always wondered what the #'step' in the barrel just forward of the front sight is for. On the #F.A.S site's pictures it shows a M4 with m203 grenade launcher, the #launcher seems to clip on just where the 'step' in the barrel is. IIRC You just answered your own question!  =) Yes, it's for the grenade launcher.  A device most normal M4 _style_ barrel owners will never get to look at in person, let alone mount on their rifles... #M16s mount the M203 without the 'step' in the barrel so why is it #needed on the M4? If you take the handguards off of a as-issued M16 (with a non-National Match heavy barrel), you will notice that the barrel under the M16's handguards is the same diameter of the step-down on a M4...  So there is a step, so to speak, that goes from forward of the chamber to the front sight _base_. /herb

#http://media.militaryphotos.net/photos/M4-Carbine/carbine07 #http://www.fas.org/man/dod-101/sys/land/m16.htm # #The above _link_s show the M4 carbine. I've always wondered what the #'step' in the barrel just forward of the front sight is for. On the #F.A.S site's pictures it shows a M4 with m203 grenade launcher, the #launcher seems to clip on just where the 'step' in the barrel is. IIRC #M16s mount the M203 without the 'step' in the barrel so why is it #needed on the M4? I'm far from an expert on the AR-15 series, but I believe that's where the full length handguard and sights were supposed to go. In my opinion it looks absolutely terrible, like it's been jerry rigged. It can't possibly help accuracy either. If I was going to buy an AR-15 carbine, I'd try for a solid barrel or I'd use full length handguards on it, which is my preference anyway. Mike We have enough youth. What we need is a fountain of SMART! AOL - You've got training wheels on your internet

# M16s mount the M203 without the 'step' in the barrel so why is it # needed on the M4? # I beleive the barrel is larger in diameter. George in Las Vegas

On 2006-07-04 06:28:15 -0500, This e-mail address is being protected from spam bots, you need JavaScript enabled to view it said: # I've always wondered what the # 'step' in the barrel just forward of the front sight is for. On the # F.A.S site's pictures it shows a M4 with m203 grenade launcher, the # launcher seems to clip on just where the 'step' in the barrel is. IIRC # M16s mount the M203 without the 'step' in the barrel so why is it # needed on the M4? The original M16 and M16A1 had a lighter profile barrel, and the narrow part of the M4's step is the same diameter as the M16 barrel at that location.  Even the M16A2 only beefed up the muzzle end of the barrel (the part you could see), but I believe under the handguards it was still the same diameter as the M16. As you guessed, with an M4 the notch is necessary for mounting an M203 on it. Incidentally, I'm no fan of the M4.  The barrel notch is only one of its annoying quirks, and not even close to being the worst.