AR questions

[Sam Colt]

Thanks, I have several 5.56, and they range from 1in7, 1in8 to 1in9. I’m thinking I would like to standardize to 1 twist rate for all.

That only makes sense if you're standardizing on one bullet weight/length for all. It's like saying you're only buying one screwdriver...

 

[TxStetson]

Thanks, I have several 5.56, and they range from 1in7, 1in8 to 1in9. I’m thinking I would like to standardize to 1 twist rate for all.

You're putting far more thought into this than it needs. Twist rates on AR barrels really isn't that important unless you're trying to shoot 77 grn SMK's in a PRS match.

 

[Darkpriest667]

I have a BCM 1:7 twist and shot this with wolf 55gr

 

[Sam7sf]

I have a BCM 1:7 twist and shot this with wolf 55gr

View attachment 261740

That’s terrible. Jk very nice especially using wolf.

 

[robertc1024]

AR-15 Barrel Twist Rates Explained

Twist rate affects bullet stability and accuracy, but what is it? Learn what twist rates are, how they're calculated, and what's best for your AR-15's calibers.

www.80-lower.com

Man - there's some stuff in there that makes no sense - such as barrel length. Bullets slide through the barrel at the beginning of hitting the rifling. They don't instantaneously start spinning because of their rotational inertia. I've never seen anything on how long it takes a bullet to fully obturate and start spinning at the rifling twist rate.

 

[Kotadaas]

It works with space magic and gun wizardry

 

[V-Tach]

OCD.............

Several us us here suffer from it.............

 

[benenglish]

Man - there's some stuff in there that makes no sense...

Ahem ...

Both have some obvious errors...

What most irritated me was the emphasis on bullet weight while downplaying projectile length. That's exactly backwards.

It's easy to write an article that's mostly correct and a useful guide to the practical concerns involved in any endeavor without truly understanding the subject in any depth. God knows I've been paid to do exactly that many, many times. I just comfort myself with the fact that he generated those stability charts with a decent calculator and there's nothing there that will result in a disastrous waste of money, even if the author has apparently never heard the name "Greenhill."

 

[Dingo]

That only makes sense if you're standardizing on one bullet weight/length for all. It's like saying you're only buying one screwdriver...

exactly, I would like to standardize in a manner of speaking. It Makes sense to me, and that’s all that matters.

 

[Dingo]

I do appreciate everyone’s input. I am learning

 

[Dingo]

You're putting far more thought into this than it needs. Twist rates on AR barrels really isn't that important unless you're trying to shoot 77 grn SMK's in a PRS match.

that’s just how my mind works, I get an idea and need to run it down.

 

[Renegade]

exactly, I would like to standardize in a manner of speaking. It Makes sense to me, and that’s all that matters.

As already stated, most have found that to be 1:7.

For example, I standardized on a 69 grain FGMM out of a 16inch 1:7 for my goto accuracy gun in 5.56.

 

[Renegade]

What most irritated me was the emphasis on bullet weight while downplaying projectile length. That's exactly backwards.

I mentioned that earlier I got deer in the headlight responses.

 

[Renegade]

Second; I am looking at an SBR with an 11.5 » barrel. Most short barrels come with a 1in7. Why, and is that enough burn?

What is it your are trying to achieve?

Generally you define the mission requirements first, then select the tool for the job.

 

[Dawico]

Man - there's some stuff in there that makes no sense - such as barrel length. Bullets slide through the barrel at the beginning of hitting the rifling. They don't instantaneously start spinning because of their rotational inertia. I've never seen anything on how long it takes a bullet to fully obturate and start spinning at the rifling twist rate.

While I have no fancy science to back my statement it's pretty fast.

Looking at a fired bullet there's not much blurr before the rifling marks even from a high powered rifle.

 

[Mohawk600]

For standard Milspec ammo (i.e. 55-62 grain) 1:7 or 1: 9 will be fine...........correct?

 

[Dingo]

What is it your are trying to achieve?

Generally you define the mission requirements first, then select the tool for the job.

almost all of my weapons are « defined », however, I sometimes want something for the hell of it. You sound too much like my wife now sir, asking a man what he needs another gun for,,, hail naw.

 

[Renegade]

almost all of my weapons are « defined », however, I sometimes want something for the hell of it. You sound too much like my wife now sir, asking a man what he needs another gun for,,, hail naw.

well then your reading comprehension sucks, nowhere did I ask “need”. I asked acheive, as I was trying to help you get the right gun

 

[cycleguy2300]

With 1:7 twist, you are good with just about any bullet weight from 50 gr. to 77 gr. With 11.5" barrel, you will lose some velocity compared to a 14" or 16" barrel. Approximately 150- 250 fps. Still moving quite fast.

Yeah, don't get your knicks in a knot over twist rate. Go 1:7 or 1:8 and call it good.

For a given length (weight) bullet, it will need a given RPM to stabilize.

The longer (heavier) the bullet, the higher RPM need to stabilize it.

RPM is directly related to both twist rate and muzzle velocity. (And muzzle velocity is directly related to barrel length for a given load)

With a short barrel you loose a little velocity so a longer bullet that worked in your 20" A1, will be a little wonky because it the forward velocity to generate the RPM from that slow 1:9 or 1:12... So you speed up that twist to 1:8 or 1:7 and those longer 64, 75 and 77s will fly straight and true. You cannot over stabilize a bullet unless it literally spins apart which can happen in a light, fast bullet in a tight twist in a longish barrel.

Like I said, just get 1:7 or 1:8 and don't worry about it...

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[cycleguy2300]

Man - there's some stuff in there that makes no sense - such as barrel length. Bullets slide through the barrel at the beginning of hitting the rifling. They don't instantaneously start spinning because of their rotational inertia. I've never seen anything on how long it takes a bullet to fully obturate and start spinning at the rifling twist rate.

Its almost instant or the rifle marks would be smeared around the bullet. Remember, it isn't moving forward from BANG at 2900fps, it takes all of the barrel to accelerate and the RPM of the bullet proportionally does as well and the rotational inertia of even a "heavy" bullet is pretty minimal with a diameter of 2.7mm of so.

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