Thinking of going with a AR 15 2O inch barrel.

CoalCrackerAl said:
Here is a read on the longer barrel advantages.
The Low Cost Light Rifle and the Benefits of the 20 inch Barrel - (gatdaily.com)
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His points are not really backed up by any quantifiable data. How much faster is a 20" over a 16" or 13.7" barrel at 25 yards? At 150 yards? Is there a relevant gain or just a feel good gain? How much "extra oomph..." is there and does it matter...does it really?

At the end of the article, he also mentioned that he likes full size handguns too. I get it...and I won't say he's wrong, but he isn't real convincing to explain the gain of the 4" versus the gain in weight and maneuverability.

But again...to each their own.
 
The 20” AR’s are cool if you want to go full M16A4-ish look. I know my former Marine buddies took a serious liking to my 20” HBAR after we all went shooting a while back. :)

Compared with a 16” HBAR, in this case a 7.62x39 version, the overall difference in length (stock extended) isn’t that great. The HBAR weight is more with the 20”, as expected, but it’s not overly cumbersome.

IMG_1569.jpeg IMG_1570.jpeg

With the 16” rifles stock retracted, it is a much larger difference in length between the two (again, as expected). :)

IMG_1571.jpeg

Stay safe.
 
CoalCrackerAl said:
From what i read they are easier on the receiver battering.
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I've put a few hundred thousand rounds through various AR rifles since @ 1993, have @ 13k+ through my 6920 alone, attended the FBI Patrol Rifle Instructor Course, and Colt's M16 L.E. Armorer's Course...this is the very first time I've ever heard "receiver battering" in reference to the AR.
 
If everything is setup correctly then there will not be any "receiver battering". Quite a few commercial 16" barrels are actually over gassed dues to the gas port being drilled bigger than it needs to be. This is done so that the rifles will run with underpowered/cheap ammo. This is part of the reason behind H2 and H3 carbine buffers are sold. Being over gassed is what causes a harsher recoil impulse.

Now to somewhat answer the original question. Yes a rifle length gas system will have a softer recoil impulse compared to a carbine length gas system. And a carbine length gas system will have a softer recoil impulse than a barrel with a piston length gas system.

There won't be much if any difference when shooting a 20" barrel with rifle length gas when using either a carbine stock and buffer or a rifle stock and rifle buffer.
 
12Bravo20 said:
Yes a rifle length gas system will have a softer recoil impulse compared to a carbine length gas system.
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All else being equal...Bingo! Not much softer, but softer. And I believe that relates to the
CoalCrackerAl said:
easier on the receiver
Click to expand...
OP's comment. After all, his thread was about barrel length only, not gas hole size, etc.
 
Nothing wrong with a 20" AR rifle

It's what Eugene Stoner designed

they run a it smoother, as the gas system is engaged further down the barrel where pressure is less.

.....but there is no "receiver battering"

All the pressure is contained in the barrel and bolt carrier group. Headspace is the barrel extension, not the receiver.

you could damn near make an upper receiver from paper mache and it would run.

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If it was a delay blowback I could see it being easier. Longer gas system is just dwell time. You can tune a 12.5 to shoot just as soft.
Buffer and spring
Adjustable gas block.
a 223 20” to me I hate. 18” is the longest I go. what are you planning to use the rifle for should be the bigger determining factor for barrel length.
mid it’s going to be a a2 build or bench rifle ok then. The only 20” I have is a 6.5 Grendel. And I’m planning to either part it out or get rid of all together. mid you just want a soft shooting rifle. Get a dissipator barrel from spinta precision. Rifle length has an 16”. They shoot great. I’ve got 3 of them in different configurations.
 
One won't go wrong with a Windham Weaponry barrel. I have a WW 20" 1-7 twist A2 barrel and it is very accurate even with M855 ammo.

The average MV for 55Gr and 62Gr ammo is around 3,000 to 3,100 FPS while the average for a 16" barrel is around 2,800 to 2,900 FPS. These are averages and different barrel twists along with different brands of 223 and 5.56x45 ammo will cause variations in MV.
 
Missing so far is that a rifle length is longer to the gas port giving more time for pressure to reduce in the chamber allowing easier extraction due to less force and also more delay in bolt movement. This is factor in reliability and softer recoil. The longer barrel beyond the gas port gives longer dwell tie for the gas to Operate the action. The rifle system is less stressful on components. Then there is the advantage of greater velocity of the bullet increasing effectiveness. That said. I like the 16 inch version better. I did like the original A1 M16 because it was much lighter than modern versions. The carbine is just handier in an already tall bulky action.
 
d2wing said:
Missing so far is that a rifle length is longer to the gas port giving more time for pressure to reduce in the chamber allowing easier extraction due to less force and also more delay in bolt movement. This is factor in reliability and softer recoil. The longer barrel beyond the gas port gives longer dwell tie for the gas to Operate the action.
Click to expand...

One of the 'quick fixes' for shorter gas systems is over-gassing, as was mentioned, although you can over-gas a rifle-length system, too, if you really got silly about it. With a properly tuned gas system, I would probably have a hard time picking out a carbine-length system vs a rifle-length system, all else being equal.

The only thing that might get 'battered' in an AR-15 would be the buffer tube, there is literally nothing else.

FWIW, I carried an M16A1 in the '80's Army, it was fine... I didn't know any better. After I got out, I bought a 20" Colt H-Bar, because it was similar to the -A1 I carried. Fast forward a years, after I built my first 16" middy-length carbine... and now the 20" AR feels like a boat oar, compared. That is not to say the 20" AR does not have it's appeal, as long as OAL weapon length isn't an issue. As far as velocity, yes, the 20" should give you additional velocity over a 16", but it is usually a moot point inside of 200yds. Just my .02 worth.
 
nastynatesfish said:
Longer gas system is just dwell time.
Click to expand...

Eh… not really.

Dwell time is the time the bullet spends PAST the port before exiting, so a 16” barrel with carbine length gas actually has longer dwell time than a 20” barrel with rifle length gas. A 16” carbine barrel has a slower bullet traveling through it, and has about 9” of dwell travel, while a 20” rifle length barrel has a faster bullet only transversing 8” of dwell length… so comparing those two common barrel configurations, a 16” carbine barrel actually has a longer dwell time than a 20” rifle barrel.

Also, the gas port position along the barrel makes a massive difference in port pressure being exposed to the gas system. Carbine ports see over 30,000 psi, while bore pressure has expanded low enough that rifle length ports are typically reduced to only seeing 20,000 or less.

Port diameter and longitudinal position, as well as the gas block design all matter - and bore diameter, powder pressure curve, cartridge choice, suppressor restriction or lack thereof, etc. We’re balancing gas and mass, lots of variables in these systems. But there are many, many combinations of gear which all work just fine together.

Also, “overgassing” is not just a common design symptom of short gas systems - it’s just more notable since they’re higher pressure and have longer dwell times. It’s exceptionally common for commercial rifles to be overgassed to promote reliable extraction and feeding.
 
It is interesting, many of the comments here about 20" barreled AR-15 is they are a "new" or "unusual" thing.

My first AR-15 experience with AR-15s was with an A2 configuration with a 20" barrel in Service Rifle competition. I guess I rate all other AR's against that standard.

I prefer a rifle that can reach out and touch someone. A longer barrel and the associated increase in velocity will extend the effective range of the rifle a bit over shorter barrels.

My main prairie dog rifle is a 26" barreled AR-15 chambered in 204 Ruger.

I'll agree short barreled AR-15's have their purposes.
 
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