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Old November 11, 2017, 08:59 AM   #1
simonrichter
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Over- and understabilization

Two questions concerning the twist rate / stabilization:

1.) Is it true that overstabilization only becomes an issue well above 300 yrds and is no problem for shorter distances? (e.g. shooting 22lr through a 1/7 AR barrel)

2.) on the other end of the scale, after which distance will an unstabilized bullet out of a smooth bore produce keyholes?
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Old November 11, 2017, 11:56 AM   #2
Art Eatman
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I've read of rifle bullet keyholes at 100 yards.
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Old November 11, 2017, 06:04 PM   #3
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An unstabilized bullet could start to tumble almost immediately. I've had undersized pistol bullets that showed evidence of tumbling at 5 yards.

Overstabilization is not really a big issue for small arms and the reason I say that is because nobody seems to be able to prove that it is. Anyway, opinions vary on that topic--precisely because of the lack of hard evidence one way or the other.
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Old November 11, 2017, 07:46 PM   #4
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Unless you are a long range rifle competitor a too fast twist "over stabilization" is not an issue until the bullets disintegrate before they hit the target. Over stabilized bullets don't keep the nose pointed in line with the trajectory path. An over stabilized bullet will keep the nose above the path of trajectory. It makes a slightly oblong hole in the paper and causes a bit more drag at long ranges. In my opinion a bullet that is over stabilized is better for hunting than one that is neutrally stable because the faster spinning bullet will assist in mushroom development.

Under stabilized bullets don't work as bullets, They tumble and don't hold a true path of flight. My rule of thumb is when there is a question of twist, more is almost always better or at least no worse for accuracy.
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Old November 11, 2017, 09:14 PM   #5
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All correct, but the OP specifically asked about shooting 22 RF through a 1:7 AR barrel. I know there are conversion kits for this, but I don't know how well they work.

Normally 223/5.56 rifles are 1:7, 1:8, or 1:9 twist. Most common bullets do pretty well with any of those, but the ones on the extreme end of the spectrum do suffer some. Most 22 RF barrels are 1:16. That is a pretty big difference. A 36 or 40 gr 22 RF designed to be fired in a 1:16 barrel might not do well in a 1:7 twist. It may do fine, but if so why do 22 RF rifles not come with faster twists.

I simply don't know. While others have given correct answers in a general way, I don't think anyone has addressed the specific question.
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Old November 11, 2017, 10:44 PM   #6
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I believe that understablized bullets don't tumble, but the nose first spin transitions into a flat spin similar to the flat spin of a stalled airplane. They hit the targets sideways but if you put several targets in the bullet's path, the bullet will hit each target sideways with the bullet's nose pointing in different directions in each target.
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Old November 12, 2017, 04:33 AM   #7
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Someone told me once that for the real short mouse guns, the fact that they do have a rifling is owed more to BTF regulations than to an actual technical necessity. Form this statement I deducted that for the first few yards (the typical engagement distance for such small guns), the bullet does still fly nose first...


So maybe it's safe to say that while a smooth bore is kind of useless (and kind of contradicting the very idea) for rifles, it is not such a big issue with short barrels anyway intended for very close distances?
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Old November 12, 2017, 09:11 AM   #8
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According to Hornady their 105gr. Match bullet wouldn't stabilize out of the 1:10 twist barrel of my wife's Rossi R243. This was over the phone, hence a live person.

I also checked the twist rate calculator at Bergers website. It also said unstable.

Never had any evidence of it out to 500 yards.

So with no evidence of keyholing out to 500, was it stable?
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Old November 12, 2017, 09:18 AM   #9
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Quote:
So with no evidence of keyholing out to 500, was it stable?
Was is consistent?
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Old November 12, 2017, 10:16 AM   #10
Jim Watson
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Quote:
Someone told me once that for the real short mouse guns, the fact that they do have a rifling is owed more to BTF regulations than to an actual technical necessity. Form this statement I deducted that for the first few yards (the typical engagement distance for such small guns), the bullet does still fly nose first...
People will tell you a lot of things. Not all of them are so and can lead to false deductions.

Even a short rifled section will spin the bullet for gyroscopic stability.
Let's say you have a 9mm P, often found with rifling of one turn in 10 inches. In a 4 inch barrel, then the bullet makes less than half a turn before it exits. But it is spinning at the RATE of one turn per 10 inches of travel towards the target. If you convert it to a Baby Luger with a two inch barrel, about 1.25" of rifling, it will still spin the bullet at the same rate.


My AR 15 is not particularly accurate with its .22 LR conversion. It may be due to the fast twist meant for longer, heavier bullets, but there are other factors.
First, the bullet has to travel the length of the .223 round through the chamber insert, which is not a precise match to the barrel of the rifle.
Then its .222" bullet has to jump to the .224" centerfire barrel.
And what will the edge of the gas port do to a lead bullet?
None of that can be good for the soft long rifle bullet.

Last edited by Jim Watson; November 12, 2017 at 10:22 AM.
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Old November 12, 2017, 10:53 AM   #11
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Jim, would you suggest getting a dedicated .22lr upper over a conversion?
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Old November 12, 2017, 12:55 PM   #12
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I have fired pistol bullets that are stable in a 1: 16 twist from a rifle with a 1:10 twist and had superb accuracy with them. The bullet was a Sierra 158 JHP .357 bullet fired from a custom 358 Win. in a Remington 700 action. The bullet is designed for 1600 fps and from my rifle it was launched at 2705 fps. At 100 yards it shoots average groups of .33" center to center and the best group I got with them was .300" at 100 yards.

The only difference that I see between my experience and the .22 rimfire question is that the bullet is soft lead and there is no increase in velocity. There are at least two pistols mass produced with a 1:10 twist in 9mm. Faster twist will not interfere with accuracy. I have thought of putting a new barrel on my .22 RF rifle with a faster twist. I believe it will aid in accuracy through the transonic zone of flight.
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Old November 12, 2017, 04:23 PM   #13
hdwhit
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Quote:
simonricheter:
Two questions concerning the twist rate / stabilization:
1.) Is it true that overstabilization only becomes an issue well above 300 yrds and is no problem for shorter distances? (e.g. shooting 22lr through a 1/7 AR barrel)
What do you mean by "overstabilization"? If a bullet is stable, it is stable. You can't really make it "too stable". If, on the other hand, you're referring to spinning a bullet so fast it exceeds its mechanical limits, I have observed 40 grain bullets launched at nearly 4,000 fps (spinning at more than 300,000 rpm) disintegrate into a puff of gray "smoke" about 50 yards from the muzzle.

So, "overstabilization" becomes a problem at the point the trigger is pulled, not 300 yards downrange.

Quote:
2.) on the other end of the scale, after which distance will an unstabilized bullet out of a smooth bore produce keyholes?
Based on field surgeon reports from the Revolutionary War and the War of 1812, bullets fired from a smooth bore barrel begin to tumble almost immediately.
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Old November 12, 2017, 04:32 PM   #14
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simonrichter, what is the point of this post?

Are you seeking to find an "optimal" twist rate?

Are you trying to figure out whether you can use a 22LR conversion kit in your AR?

As previously explained in responses to similar posts, faster twist rates are needed to stabilize longer bullets. The need for stabilization is dependent upon length, not weight. Because the length of a gilding metal jacketed lead core bullet is roughly proportional to its weight, charts matching twist rates to bullet weight are often published, but the publishers of such charts are using weight as a proxy for length.

It is how fast a bullet is spun that determines whether or not it will exceed its mechanical limits. A 22LR bullet, launched around 1200 fps is in no danger of being spun so fast that it disintegrates on its way to the target our of any rifle capable of firing 223/5.56 ammunition.
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Old November 12, 2017, 04:39 PM   #15
OzeanJaeger
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I pretty much agree with that.

Berger’s tool works for their bullets, but not so much trying to extrapolate to others using weight.

http://www.bergerbullets.com/twist-rate-calculator/
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Old November 12, 2017, 09:38 PM   #16
std7mag
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Nanuk,

Very consistant.

I really don't want to piss my wife off....
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Old November 13, 2017, 01:25 PM   #17
simonrichter
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Thanks for the replies so far. The first question was indeed meant to help me decide whether to buy a swap-in conversion which I now think will indeed do.

The second question was just out of curiosity, admittedly there are not too many smooth bore pistols, apart from the Liberator, maybe
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Old November 14, 2017, 01:24 AM   #18
Jim Watson
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If you very much like shooting the AR in .22 LR but the conversion is not accurate enough to suit you, the chamber insert can be removed and the conversion's bolt fitted to a straight barrel with proper diameter and twist.
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Old November 14, 2017, 12:30 PM   #19
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223/5.56 heavy bullet (> 55 gr.) start to become unstable about 80 yards in the 1:12 twist M16A1 barrel. They may not keyhole, but the accuracy does start to go south.

The Army used the M261 sub cal device to use 22 Rem Fire in the 'A1. With its 1:12 twist best accuracy was a 50 feet. It worked at 25 yards but the accuracy wasnt there.

There has always been a need for weapons training where outdoor ranges werent available and reduced loads for gallery shooting has been around since the days of 45-70 Model 1873s. Older military marksmanship and reloading manuals have references these gallery loads. The M261 was the latest attempt that I'm aware of.

I have tried to shoot a 100 yard reduced NRA high power match using the M261 without much success.

I havent tried to use the M261 & 22 RF in the 1:7 twist barrels, in the next few days I'll try it and see what happens.

M261 Sub Cal Device



This is my winning AK NG team at a trip to Nashville to compete with winning teams of other states, shooting the M261 at 50 ft.



This next is a test the Army conducted comparing the 1:12 and 1:7 twist barrels. It doesnt cover the 22 RF but gives an idea of what happens with different bullet weights.



Of course there are exceptions to every rule. It certainly doesn't hurt to try 22s in a AR to see where the accuracy in your rifle starts to go south.

I know in my 1:12 ARs this occurs between 60-80 yards but my 1:12 Rem. 700 BDL Var does group well at 100 yards using 62 gr Speer LE ammo. My 1:12 SP1 doesnt.
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Old November 15, 2017, 01:31 PM   #20
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I've experienced keyholing at 20 yards with a .220 swift attempting to run the long for weight 53 hornady vmax. Already anywhere within an 18 inch circle at that range too. Doesn't take much distance at all. I suspect unstable bullets of higher velocity will deviate from their intended path more rapidly than slow moving projectiles. Stability is more about overall projectile length and bearing surface than it is about weight. 55 grain flat base bullets shot lights out in the same rifle. Twist was 1-14 I believe.
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