I am wondering is the M4 barrel considered as a light barrel or just a hvy barrel with the m203 cutout?
I think that it is the later, but my friend insist that it is a light barrel. Would you guys help clarify the debate.
So according to the definiton and the picture below :
stepped: New barrel for the M4 carbine designed specifically with a "step" to accomodate the M203 grenade launcher.
The M4 barrel is a 'light' barrle, but not a lightweight style (ala the Bushmaster A1 style Lightweight barrel).
Under the handguards the barrel is around .60" in diameter. Your typical AR clone maker uses an HBAR that is around .98" in diameter. From the front sight forward the barrel is around .75" in diameter. This is the "heavy part" of an M4 barrel (like the M16A2 - its light under the handguards also). The cut the step to allow attachmetn of an M203.
If you go to Bushmaster's Website you can see the difference in an HBAR 14.5" barrel (2.5 lbs) versus the M4 (2.0 lbs). The Bushmaster "lightweight" barrel is a few ounces lighter than the M4.
The M4A1 is being issued with a new heavier barrel to help with all the full-auto fire the Special Forces practices with. This will be a special issue barrel (not for general use on all M4s).
I am little confused by your statement above. You make it sound like there are 3 different diameters on the barrel. One under the handguard, one from the fron sight forward and then 3 ?
Maybe you were saying that the AR clones are .98, does that mean that the .98 replaces the .75?
I am thinking that under the hanguard is .60 in diameter then from the front sight forward to the cutout is .98. then .60 for the cutout, and after the cut out goes back to .98.
Is this a correct assumption?
There is a lot of taper under the barrel so we are going to be using general numbers. Note I mentioned only 2 diameters per barrel. The typical AR has an HBAR barrel wich is heavier and less expensive to produce than the lighter weight government profile barrels. My M4 wannabe sports a Bushmaster M4 profile barrel and my 20" rifle has a M16A2 profile barrel (it was orginally an HBAR but I had Kurt's Kustom turn it down to the M16A2 specs).
In an M16A2 or M4 barrel (or even the M16A1) the barrel tapers down to roughly .60" just forward of the chamber to the front sight.
The civilan HBARS this area stays at roughly .98" (it varies from manufacture to manufacture but is at minium .9")
From under the front sight to the end of the muzzle ALL HBARS (civlian) and the M16A2 and M4 barrels are roughly .75".
M16A1 barrels taper down a bit finer (just under .60") to the muzzle
Now this is a ROUGH idea of what the barrels are profiled as. In reality its a bit more dynamic (i.e. I didn't take into consideration the step down for the flash suppressor threads) and the Military barrels are a bit smaller than the .75". The M4's M203 'cut' is roughtly .60" inches in diameter (same as it is under the barrel).
here is a picture of what the M4 barrel profile looks like:
Here is a picture of an M16A2 barrel profile:
www.bushmaster.com/shopping/barrel-assemblies/abbl20a2.asp This is a great barrel and its lighter than an HBAR 16" barrel (by 3 oz).
Note how they taper down after the chamber and taper up just before the front sight.
Now here is an HBAR 14.5:
Note after the chamber there is a 'slight' diameter change down to .98", which steps down to .75" just before the front sight (note the M4 barrel ramps up to the .75" portion).
Here is an HBAR 20":
The HBAR 20" barrels are a full pound heavier than the Govt profile M16A2 barrels.