length definition

AR/M4 AR Technical Discussion
1

what would a 16 1nch barrel be considered? mid, carbine ?:confused:

2

Midlength and carbine length refer to the length of the gas system. Barrel length doesn’t matter. The position of the gas block determines whether the system is carbine, midlength or rifle length.

On most 16" barrels, you’ll find midlength (~9") and carbine length (~7") gas systems. DPMS made a few 16" barrels with rifle length gas systems years ago.

3

would i measure from the front gas port to the rear of the barrel?

4

Yes…or just measure your gas tube. But it should be very obvious just from looking at the barrel.

5

Should be noticeable to the eye as the front sight will be farther forward and the handguards will be longer.

The one on the top is a 16" mid-length gas system, the two below it are 16" carbine gas systems.

6

First off, I didn’t know this either, and didn’t think to post a question about it, so thanks for asking the noob question without fear!!

And fellas, between the two systems what are the noticable differences in regards to operation? Such as, cycling or velocity, ect… My M&P15 appears to be Carbine. Facinating, I swear I learn something everyday on here

7

here is my understanding of it.

Carbine gas system was originally designed for barrels shorter than 16" like the Military M4 (14.5" barrel). To civilian’s are limited to 16" or longer barrels to be legal, without jumping through NFA hoops.

The extra length in the civilian legal 16" barrels with a carbine gas system causes:

  1. Increased operating pressure in the rifle
  2. More violent operation
  3. Dirtier and hotter operation of the system

There in theory would tend to make the system less reliable and increase parts wear. Don’t get me wrong it still works fine. It’s just a “tougher environment” so to speak and technically less reliable.

Going to a mid-length should yield the fallowing benefits:

  1. Lower operating pressure
  2. A less violent smoother operating system (less wear and trear on parts)
  3. a little cleaner and cooler (think less HOT) overall system

I’ve read that the Mid-length’s shoot smoother and have less perceived recoil.

I just got my mid-length upper so I don’t have any first hand experience, but can’t wait to try it out.

Personally, I think mid-length is a better option in a 16" barrel.

Hope I’ve got that right… and hope it was helpful.

8

Yep…that’s it in a nutshell. I believe the midlength gas system is ideal for the 16" barrel.

9

Technically, anything shorter than a full length rifle is a carbine. But otherwise, within the context of 16" barrels, the info here is spot on.

10

my new barrel is listed as a 16" CL and the measuerment from the gas port to the end of the chamber is 9" but it looks like the second rifle pictured, Im thinkin mid length

support your local leadslinger

11

If you’re measuring a bare barrel from the end of the chamber, I’m betting you have a carbine length system.

Here is a picture for comparison. The end of the tape isn’t quite at the end of the chamber, but it should help.

Carbine length on top - Midlength on bottom: