Author Topic: AR .223/5.56 barrel twist question  (Read 26510 times)

1911 Junkie

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Re: AR .223/5.56 barrel twist question
« Reply #10 on: February 22, 2009, 06:20:54 pm »
 In a rifle, the entire bullet is typically covered in copper or a similarly soft alloy, so the entire bullet is its
own driving band. Driving band does not mean that there is specifically a band of lead or copper wider
than the bullet as in the case of artillary shells or muzzelloaders.  It is merely the portion of the projectile
that comes into contact with the barrel.

So, unless you have a magic bullet(Arlen Spincter) that flies down the barrel without touching it, then
you must have a driving band.
"I'd love to spit some Beechnut in that dudes eye and shoot him with my old .45"  Hank Jr.

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Re: AR .223/5.56 barrel twist question
« Reply #10 on: February 22, 2009, 06:20:54 pm »

billt

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Re: AR .223/5.56 barrel twist question
« Reply #11 on: February 22, 2009, 06:51:08 pm »
Barnes bullets have "driving bands" because of their solid copper construction. They have no soft lead core to upset. The Hornady solids are similar in nature.  Bill T.
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m25operator

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Re: AR .223/5.56 barrel twist question
« Reply #12 on: February 22, 2009, 08:21:04 pm »
1911 junkie has wikepedia on his side, but I knew what driving bands were long before the internet was running down some bodies mamma's leg. The wiki version does indicate the term from military artillery shells having a specific band of softer material for the mating of shell to bore. Then go's on to say as 1911 said, " a rifle bullet is it's own driving band " then what do you call a bullet with grooves cut concentric to the bullet, with gaps in between?? Of course driving bands, not band. We have always used the term, for bullets without grooves, " surface area " A bullet without grooves has more surface area, in contact with the bore, than one with grooves in a similiar bullet design, ergo less friction, if they are both the same diameter, even less friction if the bullet has lubrication in those grooves.
http://tbn2.google.com/images?q=tbn:xHROfmuQNAjUkM:http://members.aol.com/SCOLL63101/public/GS1
http://www.lima-wiederladetechnik.de/7,62-mm/Bilder/7,62-mm-DJG-1.jpg
http://www.hurog.com/images/silver/fired_bullets.jpg
http://dutchman.rebooty.com/images/bullet2.jpg
http://www.gsgroup.co.za/magnumhv.jpg   

Notice in the photo that they have concentric rings, called driving bands, on the shank and only these match the groove diameter of the barrel. This means that the lands engage (‘bite’ into) far less copper than with conventional bullets. HVs thus build up pressure slower and in general, achieve higher velocities than conventional bullets of similar weight in any given calibre. Gerard claims that the reduced bearing surface is not the only reason why his bullets are faster, but as the explanation of this is very technical I suggest that you contact him for further details. The above information is basically all the average reloader needs to know.

The point is, driving bands are exactly that or We would not have a definition, separate bands that reduce friction with or without lubrication. They make a huge difference in cast lead bullets. Bearing surface on the other hand also makes a huge difference, 9mm bullets come to mind 1st, hollow point will always have more bearing surface over a solid, in a given bullet weight and usually more accurate, the VLD bullets have much more Bearing surface + Higher ballistic coefficient = more potential for accuracy.
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jumbofrank

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Re: AR .223/5.56 barrel twist question
« Reply #13 on: February 22, 2009, 08:46:53 pm »
Most centerfire rifle bullets don't have driving bands. Despite what it says in Wikipedia the whole bullet isn't a driving band. It has a bearing surface but that isn't a driving band. On the bullets that do have driving bands, they're wider than the rest of the bullet. The main bearing surface of the bullet rides in the bore while the driving bands are forced into the rifling. If you look at an artillery shell it's obvious why they need driving bands. The rest of the shell is steel or cast iron that won't engage the rifling. The driving band is copper or some other material that's softer than the steel of the barrel. The driving band is the only part of the shell that the rifling engraves.

BTW, Golden Saber pistol bullets have a driving band at the heel. That's the only pistol bullet I know of that's made that way. Since the jacket is brass instead of gilding metal it's harder, so the rest of the bullet is bore diameter and only the driving band fits the rifling.
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1911 Junkie

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Re: AR .223/5.56 barrel twist question
« Reply #14 on: February 22, 2009, 08:55:48 pm »
Now, now. I think somebody needs to to go take a blood pressure pill, maybe a nice relaxing haircut.
We have always used the term, for bullets without grooves, " surface area "
Why didn't you just say that in the first place?
If it will keep you from having a stroke, I'll call it "surface area".

How did the internet run down my mamma's leg? Al Gore hadn't even invented it yet.
"I'd love to spit some Beechnut in that dudes eye and shoot him with my old .45"  Hank Jr.

m25operator

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Re: AR .223/5.56 barrel twist question
« Reply #15 on: February 22, 2009, 10:55:23 pm »
1911, I said somebodies leg, your not old enough, for it to have been your momma, if your under 40, and I hope you are, please disregard the comment.
" The Pact, to defend, if not TO AVENGE '  Tarna the Tarachian.

1911 Junkie

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Re: AR .223/5.56 barrel twist question
« Reply #16 on: February 22, 2009, 11:00:56 pm »
O.K. I feel better now. ;)
"I'd love to spit some Beechnut in that dudes eye and shoot him with my old .45"  Hank Jr.

Bidah

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Re: AR .223/5.56 barrel twist question
« Reply #17 on: February 23, 2009, 09:37:31 am »
In the 1/9 twist barrels I have had good luck up to 75 grains if the barrel is a 20".  My 16" barrels generally won't do it, although I have one that will.  The 69gr bullets are meant to duplicate the 62gr penetrator round (M855) in length.  As stated, the bullets above 77/78 grains won't be mag length.

I have one with a 1/12 barrel, and it prefers the 45 to 55 grain bullets.  :)  I just had to have one retro...

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