Barrel Length, Rifling Twist and Bullet Weight
 

Barrel Length, Rifling Twist and Bullet Weight

Looking at AR's....

Can somebody give me a quick school on this?..

I understand that these 3 are related - I just haven't come across an explination of the mechanics...

Re: Barrel Length, Rifling Twist and Bullet Weight
 

I would recommend the ammo oracle but the website is kinda hosed at the moment...you might still be able to read most of it...

http://www.ammo-oracle.com/body.htm

My recommendation is 1:7 or 1:9 to accurately shoot the widest range of bullet weights, 50-80 grain...

1:9 is most common and will reliably stabilize (shoot accurately without keyholing) up to 68-69 gr. and depending on the barrel, MAY stabilize 75-77 open tip match (most effective)...you just have to shoot it and see.

Seems most of the higher end ARs (Colt military/LE, LMT, Noveske, Sabre Defense, etc) use 1:7 twist barrels almost exclusively--but not completely sure of that...

Also the longer the barrel, the higher the velocity and longer effective range of the round--20 inch is optimum, IMO.

From the Oracle:

BEST 223 combat loads (Ammo Oracle)

Okay, from best to worst:

1. Loads using the Nosler 77gr or Hornady 75gr OTM bullet. While these bullets may be slightly less accurate *in some rifles* than the Sierra MK, they offer better wounding capability. These bullets maximize terminal ballistic performance AND they extend fragmentation range over other loads, and even provide *some* fragmentation range from 10" barrels. These bullets require 1:8 or tighter twist barrels, though they may work in SOME 1:9 barrels.

- Hornady 75gr TAP (5.56 load)
- Hornady 75gr TAP or TAP-PD (.223 load)
- Black Hills loads with 75gr Hornady (.223)
- (no known factory load using the Nosler bullet)

2. Loads using the Sierra 77gr MK. Like all MK bullets, this one doesn't start to yaw until it passes through several inches of flesh, resulting in a longer "neck" area of the wound profile, and thus being rated slightly lower than the Nosler or Hornady bullets.

- Black Hills Mk262 Mod1 (5.56, cosmetic seconds are available)
- Black Hills 77gr Sierra loads (.223)
- Federal 77gr Sierra (.223)

77grain MatchKing OTM in calibrated ballistic gelatin. Note the long "neck" before fragmentation begins.


3. Loads using the 68gr Hornady OTM. Note: barrel length needs to be 14.5" or longer; these will not have enough velocity to fragment from a 10" barrel and only a couple of yards from an 11.5" barrel. 1:9 or faster twist required.

- Hornady 68gr Match (.223)
- Black Hills 68gr Hornady (.223)

4. Loads using the 69gr Sierra MK. Note: barrel length needs to be 14.5" or longer; these will not have enough velocity to fragment from a 10" barrel and only a couple of yards from an 11.5" barrel. 1:9 or faster twist required.

- Federal 69gr Sierra (.223)
- Black Hills 69gr Sierra (.223)

5. Loads using Trophy-Bonded Bear Claw bullets. The 62gr performs a bit better than the 55gr, but the 62gr bullet is ONLY available in the LEO-only Federal Tactical line. As a bonded-core bullet, these are excellent in situations with an intermediate barrier, and are the #1 performers when having to shoot through glass. Note: these soft-point bullets have an exposed lead tip and cannot be rechambered more than a few times. May not feed reliably in some rifles.

Federal Tactical 62gr TBBC (.223)
Federal Tactical 55gr TBBC (.223)
Federal Premium 55gr TBBC (.223)


6. Loads using the Winchester 64gr PowerPoint bullet. Note: these soft-point bullets have an exposed lead tip and cannot be rechambered more than a few times. May not feed reliably in some rifles. 1:10 or faster twist required.

- Winchester Supreme PowerPoint Plus (.223)
- Winchester Super-X PowerPoint (.223)


7. M193-class ammo, 55gr FMJ-BT bullet. True M193 ammo will be sealed at the bullet and primer, will have a crimped primer and bullet, and is a 5.56 pressure loading. 1:12 or faster twist required.

- Lake City M193 (genuine surplus M193; no longer available)
- Federal XM193 (seconds) or XM193PD (thirds)
- Winchester Q3131 (seconds)
- Winchester Q3131A (manufactured by IMI)
- IMI M193
- PMC, '98 and earlier
- South African M1Ax in battlepacks

8. M855-class ammo, 62gr FMJ-BT bullet with mild steel penetrator in the nose. True M193 ammo will be sealed at the bullet and primer, will have a crimped primer and bullet, and is a 5.56 pressure loading. 1:10 or faster twist required.

- Lake City M855 (genuine surplus M855; no longer available)
- Winchester M855 (genuine surplus M855; no longer available)
- Federal XM855 (seconds) or XM855PD (thirds)
- Canadian IVI (genuine surplus M855; no longer available)
- British SS-109


This list should give you an idea of what is preferred, and in what order. Obviously, many of the loads at the top are quite a bit more expensive than the loads further down (though the TBBC loads are by far the most expensive), but if you're looking just at performance, then this should be your guideline.

I might not have gotten every load out there, but you should be able figure it out if there's a similar load that I didn't mention.

ETA:

Loads To Avoid

Anything loaded with a varmint bullet; all varmint bullets in this caliber will underpenetrate from all guns. This means NO VMax bullets (including TAP loads), NO Nosler/Combined Technologies "Ballistic Tip" bullets, and so on. Varmint bullets were designed for animals no larger than 60 lbs., with the lighter bullets being designed for even smaller animals. They are NOT combat bullets, regardless of marketing to the contrary.

Any frangible bullet load. Frangible bullets are designed for short-range training, where shooting standard bullets at reactive steel targets would be (more of) a safety hazard. Usually, they are made from powdered lead or tungsten alloy inside a gilding metal jacket. They are designed to disintegrate when striking steel plates, but they are NOT designed to (nor do they accidentally) fragment in flesh.

"Armor Piercing" bullets. It is incredibly unlikely that anyone outside of the military will be able to put their hands on a single round of TRUE AP ammo in 5.56, as M995 AP ammo is a speciality item that is rarely issued to anyone but SOCOM troops, and then only on SAW belts, and only when specially requested for a specific mission. It is very expensive and in short supply, and it was designed primarily to disable equipment, NOT for wounding. Since the bullet will not fragment, it is a poor performer with regards to wound profile. This would hold true for any all-steel core or solid copper bullet as well.

Last Updated :: 4/11/2006 9:41:33 AM MDT

Re: Barrel Length, Rifling Twist and Bullet Weight
 

Hope you can read 'em. Found these charts regarding barrel length, velocity, and bullet weight:

Re: Barrel Length, Rifling Twist and Bullet Weight
 

The first M16s were designed to create a greater wounding effect with full metal jacketed bullets by under-stabilizing the bullets with a slow 1 in 12" rifled barrel. Thus the bullet started tumbleing if it hit anything. A way to get around the Geneva Convention. Fine for close range work in jungles, but bad for accurracy at longer ranges

Re: Barrel Length, Rifling Twist and Bullet Weight
 

Did any of that answer your questions, JJ?

Re: Barrel Length, Rifling Twist and Bullet Weight
 

The 1x12 twist was actually over-stabilizing the 55 grain bullet. Stoner originally designed the rifle with a 1x14 twist barrel and this gave the rifle the reputation as a devastating wound producer. Nothing wrong with the accuracy unless the bullet contacted anything like a blade of grass in flight.

Re: Barrel Length, Rifling Twist and Bullet Weight
 

I think so -- still combing through it.

Good stuff-thanks

Re: Barrel Length, Rifling Twist and Bullet Weight
 

OK-

so what I am gathering is Ideally- the shorter your bbl the tighter the twist is necessary to stabalize the projectile - If one were to wish to put say 77gr rounds downrange- he should have a longer barrel or a tighter twist...something along the lines of a 20" barrel w/ a 1:7 twist.

But for firing 55gr rounds- you'd get acceptable performance out of a 16" bbl w/ a 1:9 twist--- right?


:cheers:

Re: Barrel Length, Rifling Twist and Bullet Weight
 

A general rule of thumb: longer barrels with tighter twists provide better accuracy at longer ranges with heavier bullets. Did I get all that right? :confused_ma: The only benefit I see of a shorter barrel is weight reduction, balance, and ease of handling...

The 16" bbl with a 1:9 will shoot just fine...My Bushmaster 16" with 1:9 twist will shoot 1 inch or less groups @100 yds with 55 FMJ reloads and a 2.5X scope...:beer: The 52 grain match hp load is capable of less than .60", and 69 gr match out of the same rifle, shifts about 2 inches to the right and opens up to about 1.25 inches.

I would say the 16" barrel with any m193 or heavier bullet is sufficient for effective wounding out to 100-120 yards and the 20 inch barrel with heaviest bullets is sufficient for effective wounding out to 200 yards.

Re: Barrel Length, Rifling Twist and Bullet Weight
 

ahh - Thanks Silver -

I think you've got me schooled now...Now I can be an informed consumer:D




:coolbeer:

Re: Barrel Length, Rifling Twist and Bullet Weight
 

My pleasure...:wink:

Re: Barrel Length, Rifling Twist and Bullet Weight
 

An entire subject in a paragraph or two, huh.

Think of it this way, think of tops. Lets say you have a very short fat top; it wouldn't have to be spun very fast to keep it stable. Compare that to a top that is very narrow and long, say 2 inches wide and 3 feet tall. You would have to spin the devil out of that top to keep it stable.

So we can generalize and say that the longer a bullet is relative to its' width, the faster it will have to spin.

I've got a Savage 223 in 9 twist that will work with Hornaday 77 grain bullets. But if I had the choice I would pick a 8 or 7.8 twist barrel, it will shoot anything.

BTW: there is no such thing as over stabilize, the bullet is stable or not. The bullet is spinning faster than needed, accentuating defects in the bullet. You fix this by buying very good bullets.

Re: Barrel Length, Rifling Twist and Bullet Weight
 

:tongue_ma:

ya I know

For the sake of brevity... I just wanted to understand the correlation of componet configuration to physics..

The top is an excellent analogy.

Thanks

Re: Barrel Length, Rifling Twist and Bullet Weight
 

Sorry but I beg to differ. Bullet disintegration has been reported when firing light bullets in high twist (1:7) barrels at high velocities. Ex: 52gr BTHP match bullets in excess of 3200 fps, you sometimes get no hole downrange. This has reportedly been confirmed by placing blank paper at various ranges and observing only fragments penetrating the paper.

You CAN over spin a bullet. With the wide range of bullets available for the .223, for general shooting choose 1:9. This will adequately stabilize SS109/M855, 55 gr ball, and mid weight BTHP's.

Re: Barrel Length, Rifling Twist and Bullet Weight
 

My understanding was that bullet disintegration occurs only when very light bullets are shot at very high speeds. I guess it is an issue with some of the varmint shooters that require very flat trajectories. I haven't ever seen it myself, but i understand that you actually can see a little 'cloud' of the lead and copper 'puff' when this happens.

I have heard this called 'overspin' as opposed to 'overstabilization' which is supposedly having the symptom of the bullet not changing its angle to remain tangent to the ballistic arc, thereby causing a slight keyholing when it hits. I have heard that this is a non-issue.

Anybody have experience with either of these occurances? (I don't want to be a vector of disinformation, as seems to be so prevalent in this topic)

Re: Barrel Length, Rifling Twist and Bullet Weight
 

I have shot a 55 grain .223 out to 400 yards with a Colt HB carbine 16 in. barrel.I realize I could have been more choosy about rounds and bullet weights but we were shooting prarie dogs and the biggest worry was overheating the guns.
I'm pretty sure I had to raise up about 16 inches to get the hit.:D

QUOTE: "My understanding was that bullet disintegration occurs only when very light bullets are shot at very high speeds. I guess it is an issue with some of the varmint shooters that require very flat trajectories. I haven't ever seen it myself, but i understand that you actually can see a little 'cloud' of the lead and copper 'puff' when this happens."

Well, I shot reloads through my AR one clear, calm day using Hornady 55 SX bullets over a charge of IMR 4895 that smoked all the way down to the target--looked like a white light laser beam--only to see the bullet blow up in a puff of smoke right in front. When I checked it out, there was nothing but a gray mist all over the target with a few tiny holes scattered around...

Apparently, the thin jacket pealed right off the bullet and wind resistance vaporized the lead core into fine mist...looked pretty cool.

The warning on the box said not to exceed 3500 fps...which I doubt happened.

A different problem is "underspinning"...this is M855 green tip fired from an AR15 with 1:12 twist destabilized (keyholed) quite nicely:

Re: Barrel Length, Rifling Twist and Bullet Weight
 

Bullets do blow up into little gray clouds alright but it is because of bullet construction not weight. A lot of varmint bullets have very fragile construction so that they will fragment or expand on very small game and at slow velocities.

As someone else noted, I didn't say over spin, I said over stabilize. Rifles aren't general purpose tools, suitable for every conceivable use, there are compromises. Your ideal twist is dictated by your intended use.