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Posted: 10/1/2004 10:17:38 AM EST
I want to assemble a 16" AR and am considering the mid-length v. traditional carbine length gas block location. Is there any real advantage to placing the gas block further out? I find the carbine length forend just fine. If there is a previous discussion on this, please post pointer.

thanks
Link Posted: 10/1/2004 12:40:40 PM EST
Longer sight radius, smoother recoil impulse, some say they function better, and I am inclined to believe that.
Link Posted: 10/1/2004 2:17:54 PM EST

Originally Posted By Combat_Jack:
Longer sight radius, smoother recoil impulse, some say they function better, and I am inclined to believe that.


+1 on all that. I'm very fond of mine, and wonder why since the midlength configuration is available, anyone would choose to build carbine-length on a 16" barrel.
Link Posted: 10/1/2004 2:24:22 PM EST
Doesn't it potentially affect the gas system, because there is less distance between gas tube/block and end of barrel, therefore less amount of gas to blow back bolt?
Link Posted: 10/1/2004 5:22:18 PM EST

Originally Posted By hammerpair:
Doesn't it potentially affect the gas system, because there is less distance between gas tube/block and end of barrel, therefore less amount of gas to blow back bolt?


It's about the same amount as on a 20" rifle, which the whole system was originally designed around, and it's farther up the tube so the pressure is higher. What you're worried about is NOT a problem. In fact, you have more problems going the other way, down to carbine length, as the gas is ported even higher up the pressure curb with more barrel left to go. This has caused problems, nearly all of which have eventually been worked out more or less satisfactorily over the years, to the point that the carbine/M4 length system is now fairly reliable. But the midlength is still just a better mousetrap all the way around in a 16" barrel.

Then there is the so-called "dissipator" length. More sight radius, but would seem to have reliability problems, although most of the guys who have them report that they work very well, too.

I like my midlength for a number of reasons, among them looks and handling/feel. I wish it had the ballistics and sound level of a 20" barrel, but then that's what my 20" guns are for, right?
Link Posted: 10/1/2004 5:34:41 PM EST
[Last Edit: 10/1/2004 5:36:45 PM EST by innocent_bystander]

Originally Posted By hammerpair:
Doesn't it potentially affect the gas system, because there is less distance between gas tube/block and end of barrel, therefore less amount of gas to blow back bolt?



This is called dwell time. Dwell time is how long the port sees pressure. The pressure starts when the bullet passes the port and ends when the bullet leaves the barrel. The midlength has the same dwell time as the 20" rifle. However, the midlength has more port pressure because the port is closer to the breech (less volume).

Here are my two carbines. One has a 16" M4 barrel and the other has a 16" lightweight midlength. They are identical except for the barrels and ARMS vs. LaRue mounts and sights. The recoil impulse in the midlength is a bit softer.

Link Posted: 10/2/2004 5:23:02 AM EST
thanks for all the great info. Ya'll a great source.
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