5.56-223 from 10.5 inch Barel

An answer

TDC said:
I think you're missing the point. Regardless of how much barrel there is, the RPM is determined by the twist rate and initial velocity. Longer barrels provide for higher velocities which imparts a higher RPM. The length of the barrel and the twist rate together do not affect RPM.

TDC
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Thanx - a clear answer - a longer barrel is more accurate because higher velocity causes higher rpm , but what about a bullet that gets less than a spin, one that gets a full spin , and one that gets 2 spins.
The bullet that gets less than the one spin it needs for its weight and length is not optimately stabilized, this is agreed is it not ?
The bullet that gets more than one spin due to longer barrel has more gyroscopic inertia, why would it not be more stable ?
 
I never said or implied a 20 " barrel imparts a faster twist rate.
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Actually you did. A quote from your previous post.

Given a 10 inch barrel and a 20 inch barrel with the same twist rate excluding other factors - would the RPM, rotational velocity or spin be the same ?
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As far as uber short barrels - keyholing was not the issue in the post, accuracy from bullet stability was the topic.
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And what do you suppose an unstable bullet is gonna show on the target? That would be keyholing because it is unstable and wobbling. I bullet that is unstable, resulting in accuracy problems is gonna show keyholing on paper.

a bullet in a 1 in 9 ten inch AR gets a full spin , a 1 in 9 twenty inch 2 spins, but in a one in 7 twist AR less than a 1 spin. Less than ideal for stabilization.
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The number of rotations the bullet makes before it leaves the barrel is irrelevant. It is the rotational velocity that makes the difference.

Like a toy top - gyroscopic stability - more spins more stable.
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No. Rotational velocity = stability. Number of rotations to achieve that velocity = irrelevant

because a longer barrel give higher velocity by increasing the time period of energy transfer to the bullet. The faster a particle spirals within the barrel, the more angular momentum it gains.
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Yes thats true and I said so in the first sentence you quoted. But that is not the issue being argued here.

The bullet that gets less than the one spin it needs for its weight and length is not optimately stabilized, this is agreed is it not ?
The bullet that gets more than one spin due to longer barrel has more gyroscopic inertia, why would it not be more stable ?
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I'm not sure why you can't seem to understand that the number of rotations a bullet undergoes before leaving the barrel is simply irrelevant. It is the rotational velocity that stabilizes the bullet in flight. How many times it rotates inside the bore to achieve that rotational velocity is not a factor here.
 
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Suputin said:
Actually you did. A quote from your previous post.





And what do you suppose an unstable bullet is gonna show on the target? That would be keyholing because it is unstable and wobbling. I bullet that is unstable, resulting in accuracy problems is gonna show keyholing on paper.



The number of rotations the bullet makes before it leaves the barrel is irrelevant. It is the rotational velocity that makes the difference.



No. Rotational velocity = stability. Number of rotations to achieve that velocity = irrelevant



Yes thats true and I said so in the first sentence you quoted. But that is not the issue being argued here.
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A question is not an implication
 
chopper 1 said:
Thanx - a clear answer - a longer barrel is more accurate because higher velocity causes higher rpm , but what about a bullet that gets less than a spin, one that gets a full spin , and one that gets 2 spins.
The bullet that gets less than the one spin it needs for its weight and length is not optimately stabilized, this is agreed is it not ?
The bullet that gets more than one spin due to longer barrel has more gyroscopic inertia, why would it not be more stable ?
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The rate of twist acts like a transmission for the engine which would be the velocity. Regardless of whether or not you're running in first gear, second, third, or fourth. You're still driving. Same principle with barrel twist. The twist rate or rather the actual number of revolutions the projectile makes prior to exiting the barrel has no effect.

How much of a rotation does a quarterback impart on a thrown ball? I'd say no more than a third to 1/2 a revolution. What makes the ball fly further under stability. His change in amount of rotation(number or percentage of turns) or the speed(effort) he puts into the throw??


TDC
 
It is NOT rotational velocity - it is angular velocity. Velocity is a vector.

If you want to talk about rpm, it is rate of rotation.
 
This thread is making my head hurt with the crap being spewed by some.


I'm currently testing 70gr Black Hills "BrownTip" ammo in 11.5" guns - sub MOA results occuring in a number of the test bed guns.

My results with PMC Bronze is that is it typically 3MOA ammo. I use it for a number of demo's when accuracy is not paramount, nor terminal effects.
 
KevinB said:
This thread is making my head hurt with the crap being spewed by some.


I'm currently testing 70gr Black Hills "BrownTip" ammo in 11.5" guns - sub MOA results occuring in a number of the test bed guns.

My results with PMC Bronze is that is it typically 3MOA ammo. I use it for a number of demo's when accuracy is not paramount, nor terminal effects.
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nice, havent heard of this round, optimized for shorties huh? Is it alot better than the slightly heavier Hornady TAP stuff? Is this US contract ammo only not available to the public?
 
USP said:
nice, havent heard of this round, optimized for shorties huh? Is it alot better than the slightly heavier Hornady TAP stuff? Is this US contract ammo only not available to the public?
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Was least impressed for this overpriced, overated ammo, best I got was 1.75'' MOA group, fired on a CMMG 1:7 14.5'' upper..P&D sells TAP ammo.

Best group was BH77gr HP, about 1.25 MOA, no benchrest.

carlchevalier said:
enefgee, Did I mention that I get less than MOA with my STI AR with the same bullets on the bench without a rest (it has a 1 in 8 twist). So the shooter's the weak link theory is unfortunately CRAP! from what I've read in different publications, bullet weight and barrel twist rates are intrinsicaly linked to a rifles accuracy.
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Everybody on CGN shoots MOA...Maybe you read too much.
 
Airborn_69 said:
Was least impressed for this overpriced, overated ammo, best I got was 1.75'' MOA group, fired on a CMMG 1:7 14.5'' upper..P&D sells TAP ammo.

Best group was BH77gr HP, about 1.25 MOA, no benchrest.



Everybody on CGN shoots MOA...Maybe you read too much.
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I shoot minute of dinner plate :D

Have been thinking about getting a case of TAP from PD for awhile now.
 
The 11.5" bbl 1:7 twist AR I built shoots everything from 45gr flat base to 69gr SMK in my handloads just fine with accuracy ranging from 1MOA down to less than 1/2 MOA at up to ranges of 200M (limit of my club's rifle range.) The 55gr pills hold their own with the 62gr stuff. Match bullets, of course, provide better accuracy.

I can get 2MOA or better at 100M using 55gr FMJ stuff from American Eagle, PMC and S&B. No keyholing or other stability issues.

To be perfectly honest, I've got ARs and other 5.56/.223 rifles with bbl twists ranging from 1:12, to 1:10, to 1:9, to 1:8 & 1:7 and I've never had a problem with any of them shooting any ammo, handload or factory using bullets ranging from 45 to 69 grains. Some ARs or SIGs will show definite likes and dislikes, but nothing to the extent that you couldn't shoot it out to 200M and not expect to hit a standard gong or bullseye. Beyond that, I haven't experimented as I haven't been in a position to renew my provinical rifle association membership and try shooting at long range at the DND range in my area.
 
I you read this thread, The original Question pertained to weight and accuracy.

I dont think anybody really answered my original question. I think a lot of you people on this thread like to hear their own opinions as useless as they are.

Will a 1 in 7 twist barrel produce the same accuracy with a 55 gr bullet than a heavier projectile or not?
 
Having only tried Win 55gr, 62gr and 63gr GP90 in my LMT 10.5", my experience is that there "might" be a slight difference in accuracy between the 55gr and 62/63gr but that might have more to do with the particular batch of Q3131 I was shooting then anything.

The more significant difference was the change of POI between the lighter and heavier gr bullet.
 
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