I got finished watching a video with Larry Vickers where he claimed 14.5" was found to be the most reliable barrel length in terms  of ammo issues, high round counts, etc.

I've also heard rumblings that 11.5" might be more reliable than 10.5".

Anybody:  just what are the facts concerning barrel length and reliability?

In my non scientific experience 11.5 is better than anything shorter to a noticeable extent in 5.56

Google “why BCM chose 11.5”

I went with an 11.5 because it made sense to me.

YMMV

My 10.5 model 1 sales upper is over 11 years old.  Has over 10k rounds without hiccups. while accuracy sucks it wasn't meant to be a tack driver.  Lose tolerances make it run when dirty.

There is a lot more to it than barrel length...


Barrel length, as a function of dwell time, is a huge component of how long your bolt and similar will last...but there are a lot of other factors.


The ballpark rule was that a real MK 18 had around a 5K round service life with green tip.  You could go to 7K or so...but expect to replace a few parts...gas rings, extractor, springs, and so on...and some break bolts.


For the M4 it was 10k and replace the same parts...up to about 13-15K when it was done.  


For the A2 and A4...you was well beyond this...with bolts that had never been replaced and barrels with the rifling worn so badly that they had no rifling for the first 4 inches of bore.  


But, all of this is relative to the components, the ammo, the rates of fire, and similar...

I have an 8.5" with zero troubles.

I have a 12.5" with zero troubles (I assembled this one with low friction parts; never once lubed it; about 1500 rounds so far).

I have an 18" with zero troubles.

I have an 20" with zero troubles.

WTF is Larry Vickers?

Edit.

Just looked him up; he is an expert in stuff because he did things.

Lol
Operators gonna operate..
Are u really going to purchase 25,000 rds/reload that much and dedidcate it to one gun to come back and report the findings?
Almost no one is doing or does this.
I'm trying not to be a an ass but..
Fwiw
11.5" no issues
14.5" no issues
10.3" no issues (seems over gassed, I know.. use a H2 blablah.)
16" mid length...
Doesn't cycle Tula.

Not sure on you ideas or others of reliability but in our fantasy SHTF scenario I want what eats everything reliabily.

Everyone that gets into the science or discussions of "mah gas port on mah Crane spec URGI upper I had opened up by yadayada cuz blablabla I'm an operator, #clonelifeclonelife"
Cool. To each his own.
I love clones.
I buy(well I did til a couple weeks ago Tula 55gr off the shelf at rural King) for what it costs shipped in bulk..
If all my guns don't run that crap "reliabily"...
Well to me that's not reliable.
EMMV

What are you trying to do with the weapon?

Reliability has a couple of different meaning:
Reliable as in parts breaking more often?
Reliable as in it is finicky with ammo?

I went longer on my barrel (10.5 to 12.5) because the action isn't as harsh and the velocity gains are pretty big.  If I want short, I go with my 300blk.

I started looking into this same issue regarding bullet performance and how it relates to barrel length and velocity.

I carried a 10.5 SBR for work with issued 55gr Fed Tac Bonded at .223 pressure.

From what I found the 10.5 was serviceable figuring shots would be inside 100y and the ammo was in the top 3 performers for a barrier blind round

So it worked... albeit closer to the edge than I wanted to be.

I now carry a 12.5 gun and we are in the process of switching to 75gr Gold Dot for our guys carrying SBRs

What I want to know is in regard to issues like parts breakage, cycling reliability with different powered ammo, ability to keep working when fouled (but properly lubed), etc.

Does the extra inch and a half really matter between 10.5" and 11.5"?
 
(Suddenly I feel like I'm in a porn movie).

It depends...


The issue is the bolt trying to unlock while the brass is still pressurized (obturated) as 5.56 is a relatively straight walled case and extracting a pressurized case that is straight can strain components badly.  The cam geometry on the bolt carrier drives unlocking.  It was designed around a rifle length gas system with several inches of barrel in front of the gas port.  Also, the pressure curve on the ammo (burn rate of the powder) can vary, depending on your loads...which can also increase/decrease this if the curve is early/late as you don't want it at the peak pressure while it is simultaneously trying to unlock and extract.  


The more barrel you have in front of the port, the more time it has (generally) to do the work of unlocking, extracting, and similar...plus, the farther down the barrel that port is, the cleaner it will do this as the powder is later in the burn cycle and has reached/passed it's pressure curve...again depending on a lot of factors.  


Longer barrels are more forgiving.

H3 buffer really helps with delaying extraction till the pressure goes down.

As a reloader, I really notice the difference in the brass.

Adjustable gas blocks are also useful.
If you fully control your buffer and gas block, barrel length really doesn't matter.

No idea about longevity as I haven't put thousands of rounds through any of mine yet, but insofar as reliability, I have had 0 malfunctions through any of my 10.5" (3 of them), my 14.5", or my 16".  Mostly IMI ammunition: M193, M855, and M262.  My favorite AR pistol is a PSA CHF FN barrel 10.5" with FSB on a PSA M4A1 lower, CMMG LPK, Fostech Echo binary trigger, Toolcraft NiB BCG, and H2 buffer.  I've put probably around 1K rounds through that one since I build it in late May '19, again with 0 malfunctions of any kind. Maybe a hundred or a bit more of that were using binary mode and mag dumps just for fun.  FWIW, I use primarily Okay Surefeed 30 round magazines with a couple PMags on occasion.

If delaying extraction is what you're wanting to accomplish, using a solid buffer will be the most effective way. No matter how heavy a traditional floating weight buffer weighs, the floating weights will want to 'jump' as the gun is fired and give the weights a rearward momentum. Yes, the carrier can catch up to the weights just as extraction begins but the carrier has already begun accelerating faster because the buffer weight wasn't solid against the carrier during unlocking. A solid buffer delays unlocking and therefor extraction is also delayed more effectively than a heavier buffer alone. A solid buffer puts the full buffer weight solidly against the carrier as it starts its rearward movement.
Since you seem to be specifically trying to slow extraction, I figured this may be of use to you?

Thanks!

By accident, I did buy solid H3 buffers. H3 buffers are stupid expensive, till I found these:

kmtactical $15

By ''solid'', I'm meaning the weights don't slide inside the buffer housing (think 9mm type buffer). The buffer linked uses a steel weight rather than Tungsten weights so I'm guessing the housing itself is also made of steel, rather than aluminum. An aluminum housing uses Tungsten weights to reach 5.6oz, so that's why I'm guessing the housing is steel.
I don't know for sure but I'm guessing the steel weight is still able to reciprocate inside the housing? The Add doesn't specify that it's a solid or 9mm buffer so that's why I'm guessing the steel weight is still reciprocating? Since the housing is steel (heavier than aluminum), it's still mimicking a solid buffer because the housing itself is so heavy and more weight is guaranteed to be resting against the carrier as the bolt unlocks and the carrier begins to move. It has the benefits of floating weights plus the housing itself is heavy. It's a good choice for slowing extraction.
If I'm remembering correctly, an aluminum housing weighs about 1oz and three steel weights weigh about 2oz. Since the buffer you posted weighs 5.6oz, it means the housing weighs 3.6oz. if the steel weight weighs 2oz. The housing alone weighs as much as an H1 buffer. So, that buffer is the equivalent of using an H1 solid buffer in terms of stationary weight.

Double post

From reading the item description it seemed like it has a single steel weight. The moving weights act as an anti-bounce device. Like a dead blow hammer and absorb a lot of the shock. Surefire makes a new bolt carrier where the weights are built into the carrier and it also has a different cam path.

It doesn't reciprocate, it is one solid weight, no sliding.

Shooting max loads, with slow burning high max velocity powders out of an 8.5 inch barrel is tough on brass. The residual pressure as the bullet passes the port is still really high, thereby pressing the case tight onto the chamber walls. Rims will get bent just enough to make some of them not fit in a shell holder.

The weights in the buffer actually want to remain stationary, and as the recoil impulse moves the rifle into your shoulder, the weights end up against the front of the buffer, they do not travel rearward.
Take a jar, put something inside, and simulate recoil of the rifle. Whatever you put in the jar will travel toward the muzzle end, exactly the opposite of what you stated. It is physics.

I forgot to add, the reciprocating weights in the buffer also help eliminate bolt bounce, which is more common in blowback systems like an AR9. They also help to some extent in an AR, as the weights move to the rear of the buffer as the spring brings it forward, acting like a dead blow hammer.

Yea, it seems logical that if the carrier moves rearward the weights are forced against the front of the buffer and immediately slow the carrier. I don't think it's as simple as that though. Remember, the carrier moves rearward about 1/4'' before extraction begins. Also, the buffer housing has a void space that's about the same 1/4''.
What I believe happens will change slightly from cycle to cycle and change depending on how the shooter supports the weapon. Maybe the buffer weights are to the front of the housing as the gun is fired, maybe to the rear, maybe the weights are spaced apart or packed together, maybe floating in the middle, just depends. What I'm saying is that during the first 1/4'' of carrier movement (unlocking) the floating buffer weight is unpredictable at best.
When the initial blast happens (before the carrier starts to move) the weights gets jarred, and if they were forward they bounce with a rearward momentum until the carrier catches them. I'm not saying the weight is flying rearward, I'm saying the weight is no longer stationary and has a rearward momentum, as does the entire gun with them. The shooters support of the gun may be stiff of loose and this will effect how long it takes the weights to fully impact and slow the carrier. When the carrier begins to cycle and reaches the buffer weights they already had a 'rearward momentum'. You yourself stated that the recoil impulse throws the gun rearward...... the buffer weights are also moving rearward. The shooters support of the gun slows the rearward momentum of the gun faster than the floating buffer weights, if that makes sense. Yes, the carrier is moving super fast and will hit the weights and push them but the weight may not be fully affecting the carriers moving mass until the carrier has moved slightly more than 1/4'' and extraction has already begun.

OP, lots of great suggestions in here.

As a general rule of thumb the longer the barrel the better over all.  However some of the myth of the shorter barrel being less reliable comes from builds you would have come across 30 something years ago vs today.  With all of the options available today in component and ammo selection plus the easy accessibility of knowledge available online it is easier to configure a shorter reliable setup today.

Run what you brought.  10.5, 11.5, etc.... In the grand scheme of things I'll never hit the round count and accelerated rate of fire to burn out my 10.5 so I don't worry about it. If your lucky to have access to a full auto lower you can afford to blow through ammo and replace components. Barrels are cheap enough to replace anyway.  YMMV.

Yes, there is a lot going on in a very short time once you pull the trigger, and there are a lot of factors that govern bolt speed and violence of the action.
Things have certainly changed a lot since I was an armorer 42 years ago, when we only had two buffer choices, rifle and carbine. One thing that hasn't is the action of the sliding weights inside those buffers.
I don't have any solid buffers, I prefer having the sliding weights as designed by Stoner.

BCM chose 11.5 because only serious trigger pullers use 11.5.

Absolutely... all those high-speed SOF guys using 10.3" better get with the program if they ever hope to be Arfcom level operators and serious trigger pullers one day.

There is nothing wrong with 10.5" builds.  They are usually very reliable, unless the person putting it together didn't know what they were doing or inferior parts were used.  I went with a 10.3 on the recommendation of friends in the business.  They are older guys, like me, and they've told me that 10.5 or 10.3s are all they ran and never had problems.

The reason for the shift to 11.5 is for a few reasons.  First, there are always trends and fads.  Second, the 11.5 is theoretically more reliable than a 10.5.  The reason for that is dwell time.  That one extra inch increases the dwell time by 40%.  This is time that the bullet spends in the barrel with the gases having no where to go except out of the gas port.  The duration of time under which pressure is applied to the bolt is longer, so theoretically, the 11.5 SHOULD be more reliable than the 10.5.  The last reason is that at the expense of one extra inch of firearm to deal with, you get an extra 150 fps or so of velocity.  That is significant and useful, if you plan to shoot your pistol/sbr at any sort of range that doesn't qualify as close.

I went with 10.3 because I knew reliability wasn't going to be an issue.  I wanted the pistol to be as compact as possible while still having enough velocity to not castrate the 5.56 round.

If you need the velocity, going with an 11.5 might serve you well.  If you don't need the velocity and your 10.5/10.3 is running right, quit thinking about it.

As for places like BCM going with 11.5, see the above.  They are a business and they cater to their customers.  All the buzz has been about the 11.5 being more reliable and most guys that use the guns aren't gun guys.  They are just doing a dangerous job and want what they think are the best tools.  Unless they're shooting much more than 100 yards, I don't think that going with a 10.5 would be a handicap.  Besides most of them run suppressors and even on a 10.5, you need to dial the gas back to set it up right.

Foster Sturtevant designed that buffer - he was a Colt employee.  Stoner's buffer had a stack of "ring springs," which are inefficient springs that are designed to absorb energy and return virtually none of it.  They didn't work well.

The sliding weight idea appears to have been borrowed from a Hispano 20mm cannon, which had sliding weights on the bolt to prevent it from bouncing out of battery.

I watched this YouTube Video https://youtu.be/06k7y8lPuuY it boiled down to Effective 10.5 barrel use against level 3 Body Plate. I already ordered my pistol Barrel in 10.5 or I would've likely tried for a 12". I wanted my AR Pistol to have more than 30yards of Effective use. 50 some Feet and the bullet is already wanting to fragment according to some sights. Might punch holes in paper at 100 yards but it may not kill the Assailant...

just because you are a internet celeb. I have 7.5 / 10.5 that run flawless. when you have to surround yourself with young ladies you loose credibility.

I really don't think that reliability is the issue with the 10.5 vs 11.5 debate.  Both can be super reliable.  I went with 10.5 because I wanted small and on the advise of some "serious trigger pullers" I went with the 10.5.  What the longer barrels get you is more velocity which the 5.56 generally needs to be effective.

If you're gonna be that worried about the effective range of a pistol in terms of hundreds of yards, go with a 12.5.

If you go 10.5 but are worried about battering your pistol, get an adjustable gas block.  Heavier buffers are a bandaid and add to the reciprocating mass.  It's kind of funny because everyone jumps on a heavier buffer, but adjustable gas blocks can cost less.