AR porting

The simple version, without discussing port diameter:
Carbine length gas systems have the gas port located closer to the chamber so gas enters the system much hotter,under greater pressure and unlocks sooner than it would in a rifle length system.
Carbine systems are optimized for the short 14.5" barrel on an M4 carbine, when used with a 16" barreled weapon you have more gas in system, longer than intended and it makes everything even more violent.


Mid-length systems push the gas port out further in order to lower operating stresses.

Carbine length has much higher pressure at the gas port. That translates to harsher unlocking of the bolt, faster bolt cycling, and worse recoil.

As far as weight, you add a couple of inches of handguard and gas tube. For that you get longer life out of your bolt, less chance of ripping chunks of case rim off, a longer sight radius for iron sights, and an easier time staying on target shot to shot.

There's also "dwell time." Basically, it's defined by (length of barrel past the gas port in the front sight tower) divided by (projectile speed). For the sake of not having to use calculus, let's just assume that projectile speeds are the same, and just use the length of the gas tube above the barrel as a guide. I'm also skipping things like gas port sizes and gas tube diameters, but bear with me.

A 16" barrel with a midlength gas system (9") has a dwell of 7".
A 16" barrel with a carbine gas system has a dwell of 9". (hooray for first grade math! )
There are 14.5" barrels with midlength gas systems, dwell of 5.5".

The longer the dwell time, the more gas gets directed into the bolt and receiver. The more gas, the more violent the action. The more violent, the greater the recoil.

Sam Cade also has it right, but using different (but no less valid) variables.

but faster fire is possible if I am understanding correctly.

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Not that will be noticeable on a semi-auto weapon.


Cyclic rate on an actual full auto m4 carbine is upwards of 700 RPM depending on a handful of factors (condition of springs, port erosion, ammunition etc)

Outlaw_Recovery said:

Carbine length will have more recoil, more stress on parts, however lighter.
Where the mid length will have less recoil and less stress on the parts , but giving you a little extra weight.
It appears that the mid length will have a little more velocity.

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No.

There will be a negligible weight difference between mid length and carbine gas systems on 16" barrels of the same profile. We are talking fractions of an ounce for the longer gas tube.
With the same barrel length and same ammunition velocity should be identical.

There is no down side to a middy on a 16" and you even gain a couple inches of sight radius with a gas block sight.

You might want to Google the mid length gas system on 16" barrels. Lot of reports of poor functioning. They are fine on a 18" but can be problematic on a 14.5 or 16". The carbine gas system can be tamed down with buffer weight, RE spring or an adjustable gas tube.

-Middy 16" is the sweet spot for 3 gun.

-Middy 14.5" is great as long as you use good quality full power ammo, not cheap ammo.

-Carbine 14.5-16" may function more reliably with nasty or weak ammo. But has more recoil though it really isn't a big deal. I think a 16" carbine will have a smaller gas port to help.

The correct answer is that gas length is the same for ALL AR15s - about 5 to 7 inches back FROM THE MUZZLE. It's really incorrect to consider them from the chamber, as it's the timing from the bullet leaving the muzzle that counts.

Midlengths are the commercial answer to the inappropriate use of carbine length on long barrels, a holdover from BATF regulations against lengths shorter than 16". Too many 16" barrels came with carbine length and malfunctioned from bolt bounce, early bolt opening, and higher stresses. Once the makers finally realized it was either educate the public or continue to lose profit in Customer Service building actions that weren't optimal, midlength came out. It resolved a lot of problems that carbines with 16" barrels were creating for them.

Reports of midlength gas causing problems are bogus in the face of industry adoption of midlength to prevent them. It's not midlength that's a problem, it's still shooters using cheap underpowered import ammo in a gun optimized for military full power, and not bothering to lube it or use good magazines. You can't run a performance car on Coleman fuel, but that's exactly what cheap shooters try to do, and they blame the gun everytime.

Outlaw_Recovery said:

....but mostly for work carry. I do bond recovery and sometimes it get's a little hairy.

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It seems like carrying an self-loading rifle while doing Bail Bonds is a tremendously bad idea.
Having a weapon in hand is likely to be viewed as escalation of force.

What are your states laws on lethal force and bond recovery?

If you work alone where does your rifle go while you restrain them?

Outlaw_Recovery said:

I will but putting a eotech on there also so the iron sights aren't relevant.

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Batteries go dead. Electronics fail. BUIS are always a good idea.

I do know of some non-lethal rounds for 223

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Like to hear more about this.

Lethal force is allowed here

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In facilitating a bail bond recovery? What state are you in? I kinda want to read those statutes.

Outlaw_Recovery said:

Can pm you with some details if you would like.

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Sure.

Or you could just post it where we can all be enlightened.

Outlaw recovery,
The AR was originally created with the 20" barrel and to work the best in that configuration.
Now with all the variants every day including, pistols, car uppers, pistons, supressors and what not all that you need is a well tuned system. It is ok to have a carbine if that is what you like but there is a risk if you could end up overgassed. There is another interesting variant to the 16" that is the disipator upper that it is basically a barrel ported like the same 20" length with the longest sight radius but in 16" and still some of the benefits of the classic 20" system in 16" length.
If your brass ejection pattern is 1 to 3 o'clock there is a good chance you are overgassing. Look also for buffer and spring options but the most important part is to get the extra gas down.

If you want a CAR system I would seriously consider these two options in any build:
A) A adjustable gas block. This allows you adjust your dwell time.
B) Adams piston system. (This comes with 3 settings, normal, suppresed and cancel)

So with option A you can start with the closed port and the mildest ammo, (for example a PMC bronze load) and then open the screw 1/4 turn at the time until the carbine starts cycling properly. The proper ejection pattern shoudl be about 3 to 4:30 o'clock. The other way is to take your average and NATO loads and do the same but then your system will not cycle with the mildest training loads. There are gas blocks that come with a several position key for the impigment system, just exactly as some pistons do but I am not familiar with those.

One other advantages of the mid and disipator type is that the further away you are from teh chamber the gases cool off a bit and then when they come back into the bolt they come cooler. Might not be significant in normal use but in a suppressed mode you can tell by the time it takes for the whole group to come up to grilling temperature. That is when the open bolt configuration (machine gun) should be called in.

The piston also has many benefits in any configuration but it is not always necessary as some claim. I have all variants and there are things that I like and also dislike of each one.

Any system needs tuning therefore idealy any system should provide the capabiltiy to be tuned up to get the best out of it.

Cheers,
E.

Tirod said:

Reports of midlength gas causing problems are bogus in the face of industry adoption of midlength to prevent them. It's not midlength that's a problem, it's still shooters using cheap underpowered import ammo in a gun optimized for military full power, and not bothering to lube it or use good magazines. You can't run a performance car on Coleman fuel, but that's exactly what cheap shooters try to do, and they blame the gun everytime.

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+1

The problem is people continue to use cheap under powered ammo.

I would want my guns to run on any ammo I could get my hands on, so no middy 16/14.5 for me.