18 inch or 16 inch barrel

[thumper]

What advise do you people have? Should i get a new 18" medcon midlength gas port barrel or stay with my current 16" medcon carbine length barrel? Reasons for longer barrel, i want to move my front sight more forward for a better sight picture and hopefully increase my range..The weapon i have is a CMMG gas piston m4 carbine 1/7 twist medcon barrel.

[Bimmer]

... I want to move my front sight more forward for a better sight picture and hopefully increase my range...

If this the only concern, then why not get a mid-length 16" barrel? The middy sight radius is the same, regardless of how long the barrel is.

Bimmer

[Luke_Y]

If this the only concern, then why not get a mid-length 16" barrel? The middy sight radius is the same, regardless of how long the barrel is.

Bimmer

^^ +1




...Reasons for longer barrel, i want to move my front sight more forward for a better sight picture and hopefully increase my range...

Changing your sight radius will not change your sight picture...

[PlatoCATM]

Stick with a 16" middy unless you plan on shooting national match, then bump it up to an A4 style. There are so many other factors to accuracy other than splitting hairs between iron sight set-ups. How about non-CL barrel or direct impingement for accuracy's sake? Aside from all of this, your range is dictated by your ability.

At this point you should be more concerned with reliability with your chosen weapon and its "upgrades."

[Shihan]

I built a 18" SPR as I have plenty of carbine length AR's. Nice Sabre barrel etc and really wish I went with the 16" now and its my least favorite AR even with all of the goodies it has.

[yallknowho]

I don't think the 18" will give you much you don't already have. I used to have a 16" middy med con from CMMG. It was quite accurate. If you're gonna get something else, make it something much different, like a pencil barrel or an SBR.

[USMC03]

Just some food for thought:


Barrel length has nothing to do with accuracy. Depending on ammo, etc. the difference between a 16" barrel and a 20" barrel is only around 100 feet per second.

Velocity with 3 different barrel lengths using 5.56 M193 55 grain ball

14.5" barrel - 3064 feet per second
16" barrel - 3132 feet per second
20" barrel - 3259 feet per second

With this ammo, chrome lined barrels, the velocity gained from a 16" barrel to a 20" barrel is 127 feet per second......for each inch of extra barrel you are gaining 31.75 feet per second in velocity. The velocity gain isn't as great as many may have thought.


18"
-You can use a rifle length gas system on a 18" barrel (slightly smoother than a mid-length gas system). Some companies use an intermediate gas system (between a mid and rifle length gas system on 18" barrels)

-Slight velocity gain (approximately 50 - 75 feet per second - depending on barrel, ammo, etc.) at the cost of added length and added weight (on most stainless barrels a 18" barrel will weigh 6 to 8 ounces more than the exact same 16" barrel)


16"
-Shorter, lighter, more compact, thus making it a little easier to shoot from unconventional shooting positions.

-Most will use the mid-length

-Slight loss in velocity



When talking about the different gas systems on a 18" barrel, think about the distance from the gas hole to the end of the barrel. The longer that the bullet is in the barrel after the bullet passes the gas hole, the more gas that is getting pushed back through the gas tube. The end result is a sharper recoil impulse.

This is why on a 16" barrel, a mid-length gas system is slightly smoother than a carbine gas system.

A mid-length gas system on a 18" barrel is much like a carbine gas system on a 16" barrel, the recoil impulse is going to be sharper due to the longer dwell time. The distance from the gas hole to the end of the A2 flash hider on a 18" barrel with mid-length gas system is approximatley 9.5". The distance from the gas hole to the end of the A2 flash hider on a 16" barrel with carbine-length gas system is approximatley 9.5".

A intermediate gas system on a 18" barrel is simular to a mid-length gas system on a 16" barrel. The distance from the gas hole to the end of the A2 flash hider on a 18" barrel with intermediate-length gas system is approximatley 7.5". The distance from the gas hole to the end of the A2 flash hider on a 16" barrel with mid-length gas system is approximatley 7.5"

The rifle length gas system on the 18" barrel will be the softest shooting of the 3 gas systems listed. You will find that most run and gun rifle competitors and 3 gunners prefer the rifle length gas system on 18" barrels because of it's softer recoil impulse which aids in faster follow up shots.

Some good info on 1/7" vs. 1/8" twist rates can be found here: https://www.m4carbine.net/showthread.php?t=29302


Weight of different uppers:

http://www.03designgroup.com/photo/bcm-complete-ar15-upper-and-lower-receivers/icon-bcm-upper-lower.jpg
03designgroup | BCM Complete AR15 Upper and Lower Receivers http://demigodllc.com/icon/extwh3.png (http://www.03designgroup.com/reviews/bcm-complete-ar15-upper-and-lower-receivers)

[hikeeba]

USMC03 offers great info and advice regarding the 18" vs. 16" barrel conundrum. His advice helped me clear my head a few months ago during my own 18" vs. 16" decision process.



What advise do you people have? Should i get a new 18" medcon midlength gas port barrel or stay with my current 16" medcon carbine length barrel? Reasons for longer barrel, i want to move my front sight more forward for a better sight picture and hopefully increase my range..The weapon i have is a CMMG gas piston m4 carbine 1/7 twist medcon barrel.


Another way to get a longer sight radius out of the rig you have now would be to ditch the FSB (if you have one now) and go with a low-profile gas block under a longer free-float handguard, and mount a front sight on the handguard. I'm not too familiar with the CMMG piston setup, so if the piston gas block setup is an issue, you'd probably need to look into an extended handguard with a FSB cutout (DD, Troy) to see if that would be compatible/doable.

[Failure2Stop]

I don't know what kind of gas block your piston gun has, but if at all possible I would try to fit it under a 12-13 inch HG. Once you do that you will have rifle-length sight radius without having to increase barrel length.

[clickclack]

wow usmc03 droppin knowledge good read thanks

[Boss Hogg]

Great post, USMC03.

OP- are you getting a secondary upper, or replacing the barrel? If the latter, why? For a better sight picture, why not spend the money instead on a good red dot or variable power scope?

"This is why on a 16" barrel, a mid-length gas system is slightly smoother than a carbine gas system."

I'm glad you mentioned "slightly". Some guys act like if they don't have a midlength gas system with a PWS or Battle Comp muzzle device, the gun will recoil so hard that it will buck out of their hands.

I have an 18" BCM stainless barrel with rifle length gas system. Great barrel, but 16" hammer forged barrels have been my "go to" setup for range day.

[USMC03]

Thanks for the kind words, Gents.


Check this link for a bunch of pics of guys shooting a practical rifle match from 3 to 425 yards:

https://www.m4carbine.net/showthread.php?t=2475