AR gas system vs bbl length - Survivalist Forum
Survivalist Forum

Advertise Here

Go Back   Survivalist Forum > >
Articles Classifieds Donations Gallery Groups Links Store Survival Files


Military Weapons Forum AR15, AK47, SKS, H&K, Galil, CETME, FN/FAL, Tanks, Ships, Jets, Helicopters....

Advertise Here
Thread Tools Display Modes
Old 10-15-2019, 12:20 PM
Buck91 Buck91 is offline
Join Date: Dec 2015
Posts: 263
Thanks: 41
Thanked 165 Times in 103 Posts
Default AR gas system vs bbl length

Advertise Here

How much of an effect does gas system length have on velocity as opposed to barrel length in an AR platform? There are lots of tests out there, for example, of 5.56 and .223 ammo from various bbl lengths but most of them are using either all the same gas system or no gas system at all (bolt guns and cutting down the bbl).

For example, if one has a 16" carbine and a 16" midlength, would you expect any appreciable difference in .223 velocities? What about a mid vs rifle length 18 inch bbl?

Similarly, when looking at .300blk for a hunting load there are many carbine length 16 inch options. Would this have any effect on unsuppressed supers? I'm not talking about action function, simply considering velocity differences.
Quick reply to this message
Old 10-15-2019, 02:22 PM
ajole ajole is offline
Join Date: Dec 2007
Posts: 11,079
Thanks: 9,101
Thanked 25,874 Times in 8,019 Posts

I think it would be negligible, there's just not that much gas being diverted from pushing the bullet, regardless of tube length.
Quick reply to this message
Old 10-15-2019, 02:30 PM
dmas dmas is online now
Join Date: May 2009
Posts: 5,318
Thanks: 1,584
Thanked 4,711 Times in 2,551 Posts

The longer gas systems are supposed to be softer shooting, less recoil.
Quick reply to this message
Old 10-15-2019, 04:14 PM
AK_guy's Avatar
AK_guy AK_guy is offline
Eh kay vs eh are dood!
Join Date: Aug 2010
Location: Illinois
Posts: 3,304
Thanks: 5,001
Thanked 3,883 Times in 1,644 Posts

It's negligible at best.
If you are thinking about getting a 300 blackout gun with a shorter barrel you should get one with a pistol length gas system. The carbine length gas systems have a shorter dwell time and can lead to poor cycling of the action. Meaning, the shorter distance between the gas port and end of barrel allows less gasses to cycle the action and can cause failures. This has not been the case with 556 guns.
Get your concealed carry permit.
Quick reply to this message
The Following 2 Users Say Thank You to AK_guy For This Useful Post:
Old 10-15-2019, 04:46 PM
NCalHippie's Avatar
NCalHippie NCalHippie is online now
Join Date: Jun 2013
Posts: 15,392
Thanks: 34,043
Thanked 28,771 Times in 10,730 Posts

I would be more concerned with cycling the action with a short barrel than bullet speed.
Quick reply to this message
Old 10-15-2019, 06:05 PM
ImStillHere's Avatar
ImStillHere ImStillHere is offline
Wrong Side of Heaven
Join Date: Feb 2012
Posts: 3,481
Thanks: 2,392
Thanked 6,814 Times in 2,456 Posts

no cycling issues with a 7 1/2 barrel 5.56 ar pistol and a Franklin binary trigger. yes I have lost velocity but that isnt what it was purchased for.
Quick reply to this message
The Following User Says Thank You to ImStillHere For This Useful Post:
Old 10-15-2019, 10:04 PM
ksmedman's Avatar
ksmedman ksmedman is offline
Dunning-Kruger Survivor
Join Date: Jan 2011
Posts: 7,540
Thanks: 12,756
Thanked 21,867 Times in 5,610 Posts

I have a 10.3, pistol gas system.
Works like a charm, suppressed or not.

Longer barrels do yield some increase in velocity for supers, but it's pretty negligent. The round was designed for shorter barrels.
"It was always the women, and above all the young ones, who were the most bigoted adherents of the Party, the swallowers of slogans, the amateur spies and nosers−out of unorthodoxy." - Orwell, 1984
Quick reply to this message
Old 10-16-2019, 07:56 AM
MagnumWill's Avatar
MagnumWill MagnumWill is offline
Near The Glow
Join Date: Sep 2012
Location: Colorado
Posts: 901
Thanks: 2,881
Thanked 1,734 Times in 569 Posts

The OP is asking if a longer gas system decreases velocity. My experience says no. By the time the gas system even starts moving, the bullet's left the barrel.

My carbine and mid length shoot identical velocities. Barrel length naturally makes a difference as people have been stating.
Quick reply to this message
The Following User Says Thank You to MagnumWill For This Useful Post:
Old 10-18-2019, 09:02 AM
Bodhran777's Avatar
Bodhran777 Bodhran777 is offline
Join Date: Sep 2019
Location: Texas
Posts: 42
Thanks: 0
Thanked 45 Times in 22 Posts

Been a while since I looked into this topic, but I do remember some. The main variable is how much longer is the barrel compared to the gas system. The greater this difference, theoretically the more velocity you lose to friction. As soon as the propellant gas passes the gas port in the barrel, it loses its "push" due to now working to cycle the action. Therefore, a 20" barrel with a carbine gas system would have the most velocity loss (though you'll never see this setup).

For the most part, your gas system length is going to match your barrel length to negate any loss in velocity. However, the main contributing factor in my experience is your specific ammo (powder, bullet type, weight, etc.) To that end, it's worth testing different types of ammo to see what works best for you and your gun. The same ammo may not work well for different guns. For example, an old bolt action I had worked fine on Remington UMC for punching paper, but my newer bolt action (Remington, of all things) locks up when I try to run UMC, requiring me to knock the bolt open with a mallet. It's awful, but then it throws Hornaday Black like a champ.
Quick reply to this message


Quick Reply

Register Now

In order to be able to post messages on the Survivalist Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Please select your insurance company (Optional)


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools
Display Modes

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT -5. The time now is 02:29 PM.

Powered by vBulletin®
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimisation provided by DragonByte SEO (Lite) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright © Kevin Felts 2006 - 2015,
Green theme by