What are the advantages/disadvantages of using either in a carbine gas, pistol build? Looks like a few days ago everyone had a run on the 10.5 barrels and so only 11.5 I am seeing available.  Not sure if this is related to the Biden/ATF pending redefinition scare or not?  Who knows how long before the 10.5's are back in stock? Oh looking at 5.56.

The added dwell time is well worth that extra inch..

This sums it up nicely....Click here

Port size, or carrier/buffer weight, can flatten that curve.  Get what you can.  If you plan on suppressing go shorter.  I did.

Nothing wrong with 11.5, I wouldn't go shorter than 10.5".

Answers all my concerns. Thanks guys.

Ignorant people will still debate it though, and contest proven data along with why that extra inch in velocity actually matters to some people.

There's not a ton of difference.  I settled on 11.5" because I found a smoking deal, but had tons of barrels bookmarked between 10.3" to 12.5" that I would have been perfectly happy with.  Just depends on your intended use.

Ignorant? Dwell time is not the distance from the gas port to the muzzle as BCM claims. Dwell time is the point at which the bolt starts unlocking after the gas port is pressurized. But regardless of that….

Barrel length has NO impact. Gas pressure levels matched to reciprocating weight is what determines dwell time/bolt unlocking.

Getting to that point of tuning was rough, but it’s not the 90’s anymore. No longer is the standard answer a carbine buffer and a bigger gas port for a short rifle.

In addition, Molon did the math on TOS, and two inches of barrel length is a change of .00006 seconds. That means 10.5 to 11.5 results in .00003 seconds difference.

Gas system length regardless of barrel length, the amount of gas pressure allowed through the gas port, the weight of the combined bolt group and buffer, and even the buffer spring are all a hundred times more critical. The HK416, Krinkov, G36, and dozens of other rifles have stellar track records for their gas systems despite reduced “dwell times”.

To the OP, buy the best barrel at your price range that appeals to you.

I don't know what you're exactly trying to achieve here or why you chose to have a go with me, but my 11.5 never needed a heavier buffer or barrel that was chased down for a gas port hole diameter in order for the combination to work right.

And I know how dwell time works, some people here think that they're the only ones that do though.

As for ammunition, the extra inch actually does matter and has impact due to the munitions that I use and this thread proves it.

YMMV.

I would agree with the ballistics side of things.

My point is BCM is wrong about dwell time and what determines it, wasn’t going off on you per se. Different configurations require different components/specs with not just AR15’s, but with all rifles.

Also, an 11.5 certainly does have a different gas port size from all other barrel lengths. As barrel/gas system length decreases from the original 20”, so does the gas port diameter. Up until not that long ago, all 10.5’s ran a Colt spec 11.5 gas port, and in some cases even a 16 inch spec gas port.

The only reason 11.5 had the jump was because Colt put in the leg work on tuning before they released it. For decades no one put that effort into 10.5’s, so they got a bad rep.

Fair enough. My 11.5 happens to be a Colt FBI HRT SOCOM profile, and ballistics is really important me.

The whole idea of a, "short" barrel is to have the barrel, "short."

When the military was working on the CQBR and MK18 projects, they desired the shortest barrel that would remain reliable.

I was involved in a project in the 1980's to get a 10" barrel more reliable.

We didn't have the benefit of M4 feed ramps, M4 extractor springs or heavy M4 buffers.

First we found out the gas port had to be larger than ideal.

There were no heavy buffers then, but there were some odd hydraulic buffers and spring loaded buffers that helped rate of fire, but mechanically weren't very reliable.

In the mid to late 1980's Colt came out with the 9mm model.

This had a two-piece buffer that was the same weight as a later M4 H3 buffer.

This buffer was fantastic with our large gas port.

Later, Colt came out with a one piece 9mm buffer that didn't work as well with 5.56 models.

Now back to the military projects.

In the search for the shortest reliable barrel, the military starting with an M4 in 1999, decided that replacing the H buffer tungsten weight with a lighter steel buffer weight to match the carbine buffer weight would allow using the smallest gas port size.

With that in mind, they found that with a carbine buffer, a 10.5" barrel was more reliable than a 10" barrel.

The 10" barrel required removing the bayonet lug, but the 10.5" barrel did not, so it remained and at the time there were obscure accessories marketed to military and law enforcement that used the bayonet lug, but they didn't really catch on.

They also added an o-ring to extractor spring.

A couple of years later Colt got involved.

Colt switched to the H2 buffer and shortened the barrel as short that would allow the bayonet lug, which now had become a feature of the project and discarded the extractor spring o-ring.

This resulted in the 10.3" barrel.

Around the same time, Colt Canada was working on a reliable 10" barrel.

It also used the H2 buffer, but had the bayonet lug removed.

Had the military originally went to a heavier buffer, instead of lighter, the original 10" barrel length likely would have met the reliability requirements.

The original CAR15 / XM177 had a 10" barrel.

There was a desire to improve reliability even with 55 grain bullet ammo in it.

Colt lengthened the barrel to 11", but a short time later the US military requested a barrel long enough to mount an under barrel grenade launcher, resulting in the 11.5" barrel.

The original Colt carbine had a 14" barrel, that was the shortest that allowed a bayonet to be mounted, but the bayonet was supported by the front of the flash hider instead of the rear, over its threads on the barrel.

The US military requested the distance from the muzzle to the bayonet be the same as on the full length rifle, resulting the 14.5" barrel.

With a shorter barrel, the gas timing is shortened, requiring a stronger impulse through the gas system to cycle the action.

This is accomplished by inlarging the gas port.

The counter and control the stronger, sharper impulse caused by the larger gas port, a heavier buffer is desired.

With one of those 10.5" barrels with a, "big" gas port, just go straight to an H3 buffer and call it good.

Some of the minimum gas port version can use H2 buffers.

Same for 11.5" barrels with large and small ports,H3 and H2 buffers, but nearly always heavier than an H buffer.

You sir, are an absolute attribute to the site. Kinda crazy in modern times to think of a bayonet having such a large impact on the design of a rifle.

I run a 4.3 KVP with a .070 port and it runs almost as soft as my middy but still cycles 223 loads. Makes a guy wonder how much money and man hours went into making a 10.5 work.

Excellent information. I enjoyed reading that. Thank you.

Great post.

Well just my luck I was getting ready to purchase the ballistic advantage 11.5 and they are out of gas blocks. I want this pinned but I don't want the hassles of having to send to adco or finding someone local and hoping they know what they are doing. Aero has the same in stock but apparently they won't pin the blocks. I just want a low pro. Anyone have other options? Unreal they are out of gas blocks.

Centurion Arms will pin their blocks for you on their barrels. Faxon I think does it too with their barrels as well if ordering direct as well. SLR will pin their blocks on any barrel you would provide.

Pinned is better, but at this point I have hundreds of thousands of rounds through set screw gas blocks with none ever coming loose. Only catch is I only run dimpled barrels.

Everything is out of stock at the alternative places. What about this for a pistol build? It's obviously a different profile but weight is no issue and I don't need the nikel boron extension but either way it's available and with the gas block included and pinned its about the same price as the barrels in stock. How would this function compared to the govt profile options in botu 10.5 and 11.5.?  


https://www.ballisticadvantage.com/10-3-5-56-ba-hanson-carbine-length-ar-15-barrel-w-lo-pro-performance-series.html

IM sent

Ahhh, but people who aren't concerned about that 75 FPS when it comes to their CQB weapon are "ignorant"

First off this isn't GD, how about you grow up and stop post stalking me and taking everything I've said so personal because none of it was ever directed at you to begin with, hm?

And second, projecting your ignorance much? Your numbers are still wrong, even the other posters from that last short barrel thread pointed it out to you. In certain circles, they'd call that a clue.

Third, did you build a better scope leveler for $20 than the one from Badger Ordinance? Members did ask you to make one and market it so they can buy it or to stop trolling me, but you chose instead to beat feet and run away, never to be heard from again in that thread.

But since you made yourself become said subject, showing that the shoe does indeed fit.

Find something more positive to do, your first post today in this thread was this morning. Your second was late in the evening, suggesting nefarious reasons, I do believe that post stalking is a CoC violation. Maybe you should put me on ignore and save yourself some future pains, because you've been problematic with me in each thread we've both happened to post in. From the first time where you self triggered because I recommended using an MI reaction bar and contested that the OP of that thread only needs two C clamps and two blocks of wood. I don't even know why you're so vividly fragile when it comes to others suggesting to spend money on things you're obviously vehemently opposed to or in this case, emotionally involved in because you own a 10.5.

And as said elsewhere, you have a major problem where you think that your opinion matters more than anyone else's and superimpose your own insufferable values and experiences over others. Take the repeated hints and leave me alone. We'd both benefit from you doing that greatly.

@Lancelot

Can something be done please?

Hey now, I’ve gone rounds with s4 before. It’s a right of passage. He’s a typically decent and knowledgeable dude.

As I have said before, you need to follow your own advice.  Pot and kettle thing, y'know

I am the easiest going dude you would ever meet, but I refuse to be PC.  If I see BS I call out BS.  Peace and love to all

I have two DD Mk18's and the only reason I bought them was to be clone worthy.

11.5" is probably the shortest barrel you'll ever need. I have a 13.7" barrel with a Surefire Warcomp pinned and welded to 16" and it's perfect IMO. No tax, no problems and plenty short. It looks a lot shorter than it is.

12.5" is very handy and every bit as maneuverable.

So I am validated, you are staking me indeed as this is no longer a 10.5 or an 11.5 thread to you. This is about you versus me. And it's been plainly apparent for quite some time.

And as I too have said before, grow up and stop being a child. In every thread that we've had conflict in, it was you chasing after me, nothing I had said was ever directed at you yet you took each one personal.

For a person who said that he will call out any BS, you certainly have given enough BS yourself.

Serious question here, are you a boomer? It would explain the narcissisms in your posts and why you've childishly decided to stalk my posts at faux reasons to be upset with what I suggest or give an opinion of, that you've so emotionally and vehemently opposed.

Use the ignore or take it to the pit, or have the maturity to MYOB at things that trigger you. You are far from easy going, not even close.

I think you need to start a pit thread, if anyone. You ruined that recent lightweight thread doing the same thing here, where you make things personal that aren’t.

It’s the internet and we all have different favorite colors. It’s all good and no need to take it to the next level.

If you were being stalked from thread to thread too, you'd be acting just the same as any normal person would because there's enough cause to show that he is making it very personal. How else would you explain his behaviors in each thread that he has chased me in?

And you're right, it is the internet. I should be able to post harmless suggestions that doesn't effect anyone, without the drama he has seriously invested in.

This B.S. is OVER!