I'm just wondering, how long the barrel canbe before the bullet stops accelerating? And how long can the barrel be before there is no improvement in inherent acuracy?

you don't know how bad I want to say 87 inches...

Barrel length has nothing to do with accuracy, so scratch that from the discussion.


As for length, the longest barrels for .223 I've seen are 24", but I am sure 26" is doable.


Here's the problem. It all depends on bullet weight/style and powder type/charge. For a long barrel, you'd want a slow burning powder. Shorter barrels need faster burning powders to get the bullet up to speed. You'd want as much of that powder charge to be converted into gas pressure before the bullet exists the barrel. When you see a big flash, that is essentially the unused powder/pressure burning outside of the barrel where it can no longer generate pressure, and thus, no more velocity.


Here's an example. If you shoot a .22mag out of a 20" or greater barrel, there is no flash. But if you shoot a 22mag out of a 2" snubnose revolver, there is a fireball. The difference in velocity will be nearly 800fps. In short barreled handguns, the 9mm is much more efficient than the 357magnum. The 357 makes a nasty fireball and the end result is barely anymore FPS than a comparable 9mm.


I don't know what the max barrel is. I'm sure you could probably find a bullet and slow burning powder to fully utilize a 28" barrel...who knows. Just a guess. A .223 load optimized for a 20" barrel (like 2230c) is going to be less efficient than a powder like 2520 used in a 24-26" barrel. Likewise, a faster powder is going to be wasteful in a long barrel. If you make a load with a fast powder for a short barreled rifle, you might not see a gain at all in a 24" barrel because whatever powder was in that charge was converted into pressure before say 16" of barrel...(just an example) the bullet is then traveling through rifling, incuring uneccessary friction without any more significant push on it.


.22LR is said to reach max velocity at around 16" of barrel (not talking about hypervelocity or high velocity)...many of the match loads are just under subsonic. Many longer barrels were thought to have been more accurate because of length, but was really happneing is, these 26" barrels were keeping the bullet subsonic...making them more accurate (since not having to break the sound barrier).

Thanks for you well thought out response. I used a 28" barrel to shoot .22 in NRA matches as a kid.  It was a very accurate, whisper quiet barrel!  I should rephrase  my question then to: What is the longest barrel for a 5.56mm SAAMI load  with 55 grain bullet or 62 grain bullet before it stops accelerating? More briefly, what is the longest barrel that will wring all the power from a milsurp 5.56 mm round?

Quoted: Thanks for you well thought out response. I used a 28" barrel to shoot .22 in NRA matches as a kid.  It was a very accurate, whisper quiet barrel!  I should rephrase  my question then to: What is the longest barrel for a 5.56mm SAAMI load  with 55 grain bullet or 62 grain bullet before it stops accelerating? More briefly, what is the longest barrel that will wring all the power from a milsurp 5.56 mm round?

Bushmaster used to sell 26" barrels. I have a Bushmaster 24" HBAR (4150 steel, chrome lined bore, 5.56N chamber).

I had a 28" AR barrel for a custom build I did for a guy, Krieger makes them.

What we need is a teleportation device attached at the end of the muzzle so that it instantaneously transports the speeding projectile to your target bypassing the need for bulky barrels and trajectory/wind adjustments.

Longer barrels are mistakingly thought to be more accurate. They do have a longer sight radius for iron sights, so maybe that is what got people thinking they were more accurate. They tend to be less accurate because they are less stiff for any given thickness.

They do have more velocity though, so for long range shooting, there is less wind correction.

Quoted: Thanks for you well thought out response. I used a 28" barrel to shoot .22 in NRA matches as a kid.  It was a very accurate, whisper quiet barrel!  I should rephrase  my question then to: What is the longest barrel for a 5.56mm SAAMI load  with 55 grain bullet or 62 grain bullet before it stops accelerating? More briefly, what is the longest barrel that will wring all the power from a milsurp 5.56 mm round?

I see a problem with your question.   It lies not with the barrel but the fact you mentioned milsurp ammo.
The longer custom match barrel is associated with accuracy.  Milsurp ammo will not give you the accuracy the barrel is capable of.

Befeore you decide on a longer barrel change ammo or your no better off then you would be with a stock M4.

Quoted: What we need is a teleportation device attached at the end of the muzzle so that it instantaneously transports the speeding projectile to your target bypassing the need for bulky barrels and trajectory/wind adjustments.

Star Trek did it!!!  Star Trek did it!!!

DS9 if I remember correctly...

I believe the four inches gained between a 20 and a 24 give a gain of 120 fps, while a supressor usually adds 40-50 fps.  Were I to add four inches, I'd get a can.

Quoted: Quoted: What we need is a teleportation device attached at the end of the muzzle so that it instantaneously transports the speeding projectile to your target bypassing the need for bulky barrels and trajectory/wind adjustments. Star Trek did it!!!  Star Trek did it!!! DS9 if I remember correctly...

Interesting
War on Terror 2459: Longest shot reported by US Marine Sniper- 35,000 mile headshot w/ 45 Auto

Quoted: I believe the four inches gained between a 20 and a 24 give a gain of 120 fps, while a supressor usually adds 40-50 fps.  Were I to add four inches, I'd get a can.

The can is also a few grand ($$), requires paperwork, tax stamp, and has a limited lifespan (well, more limited than a barrel). I agree that a can is more versatile but after owning a 24" AR-15 and a 16" AR-15 (M4 profile), I probably should have gone with the carbine first.

Quoted: Quoted: I believe the four inches gained between a 20 and a 24 give a gain of 120 fps, while a supressor usually adds 40-50 fps.  Were I to add four inches, I'd get a can. The can is also a few grand ($$), requires paperwork, tax stamp, and has a limited lifespan (well, more limited than a barrel). I agree that a can is more versatile but after owning a 24" AR-15 and a 16" AR-15 (M4 profile), I probably should have gone with the carbine first.

Dude!

A can costs $375, +$200 tax, a 75 day wait, and should last as long as a barrel (some last more; they have come a long way).

Add to that the sound reuction and velocity/accuracy increase, and you are on your way.

Quoted: Thanks for you well thought out response. I used a 28" barrel to shoot .22 in NRA matches as a kid.  It was a very accurate, whisper quiet barrel!  I should rephrase  my question then to: What is the longest barrel for a 5.56mm SAAMI load  with 55 grain bullet or 62 grain bullet before it stops accelerating? More briefly, what is the longest barrel that will wring all the power from a milsurp 5.56 mm round?

FYI, 5.56mm is a NATO standard. 223 Remington is a SAAMI standard.

Quoted: 87 inches

That is optimal!

Quoted: Quoted: What we need is a teleportation device attached at the end of the muzzle so that it instantaneously transports the speeding projectile to your target bypassing the need for bulky barrels and trajectory/wind adjustments. Star Trek did it!!!  Star Trek did it!!! DS9 if I remember correctly...

Heck if I gotta use the transporter...A bullet?...Fohgettaboudit...I'ma gonna droppa a piano on 'em

Quoted: you don't know how bad I want to say 87 inches...

You just did!!!


Travis

Quoted: Quoted: Quoted: What we need is a teleportation device attached at the end of the muzzle so that it instantaneously transports the speeding projectile to your target bypassing the need for bulky barrels and trajectory/wind adjustments. Star Trek did it!!!  Star Trek did it!!! DS9 if I remember correctly... Heck if I gotta use the transporter...A bullet?...Fohgettaboudit...I'ma gonna droppa a piano on 'em

It was a micro transporter mounted on the end of the barrel.  Pretty cool idea actually...

Quoted: Quoted: Quoted: I believe the four inches gained between a 20 and a 24 give a gain of 120 fps, while a supressor usually adds 40-50 fps.  Were I to add four inches, I'd get a can. The can is also a few grand ($$), requires paperwork, tax stamp, and has a limited lifespan (well, more limited than a barrel). I agree that a can is more versatile but after owning a 24" AR-15 and a 16" AR-15 (M4 profile), I probably should have gone with the carbine first. Dude! A can costs $375, +$200 tax, a 75 day wait, and should last as long as a barrel (some last more; they have come a long way). Add to that the sound reuction and velocity/accuracy increase, and you are on your way.

Where can I find cans for AR-15s that cost $375? Point me in the right direction?

What would be cool to know is how long of a barrel is needed to have the bullet just fall out of the muzzle.  THAT would be the longest a 5.56 barrel can be.

Quoted: Quoted: Dude! A can costs $375, +$200 tax, a 75 day wait, and should last as long as a barrel (some last more; they have come a long way). Add to that the sound reuction and velocity/accuracy increase, and you are on your way. Where can I find cans for AR-15s that cost $375? Point me in the right direction?

Ask and ye shalt receive....

www.tacticalinc.com/tac16-ar15-556mm-suppressor-p-44.html


Woody

Gemtech M4-02.

Quoted: Quoted: Quoted: Quoted: What we need is a teleportation device attached at the end of the muzzle so that it instantaneously transports the speeding projectile to your target bypassing the need for bulky barrels and trajectory/wind adjustments. Star Trek did it!!!  Star Trek did it!!! DS9 if I remember correctly... Heck if I gotta use the transporter...A bullet?...Fohgettaboudit...I'ma gonna droppa a piano on 'em It was a micro transporter mounted on the end of the barrel.  Pretty cool idea actually...

If they could teleport that accurately, why even need the velocity from a barrel?  Why not just have a teleportation gun that teleports small explosive charges inside your enemies?

Or teleport a hungry cokcroach inside their brains?  

Extra long barrels on an AR15/M16 are a waste unless the gas system is also made longer. Once the projectile passes the gas port the pressure behind it drops off rapidly.

Quoted: Extra long barrels on an AR15/M16 are a waste unless the gas system is also made longer. Once the projectile passes the gas port the pressure behind it drops off rapidly.

Krieger barrels makes one as well a extended gas tube to enhance the 28" barrel, it reduces port pressures to a better level.

Quoted: Quoted: 87 inches That is optimal!

87 Centimeters might work good too.