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Does velocity affect stabilization?
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Picture of Mike_Dettorre
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Not sure where to post this.

But does velocity affect stabilization. I am not talking about the extremes of say 1500 fps versus 3000 fps.

I am more referring to is optimum twist rate affected by say 300 fps. As in if you were building a 308 win versus a 300 Win Mag and you were going to shoot 180 grn bullets in both would you choose a different twist rate?


Mike

Legistine actu quod scripsi?

Never under estimate the internet community's ability to reply to your post with their personal rant about their tangentially related, single occurrence issue.




What I have learned on AR, since 2001:
1. The proper answer to: Where is the best place in town to get a steak dinner? is…You should go to Mel's Diner and get the fried chicken.
2. Big game animals can tell the difference between .015 of an inch in diameter, 15 grains of bullet weight, and 150 fps.
3. There is a difference in the performance of two identical projectiles launched at the same velocity if they came from different cartridges.
4. While a double rifle is the perfect DGR, every 375HH bolt gun needs to be modified to carry at least 5 down.
5. While a floor plate and detachable box magazine both use a mechanical latch, only the floor plate latch is reliable. Disregard the fact that every modern military rifle uses a detachable box magazine.
6. The Remington 700 is unreliable regardless of the fact it is the basis of the USMC M40 sniper rifle for 40+ years with no changes to the receiver or extractor and is the choice of more military and law enforcement sniper units than any other rifle.
7. PF actions are not suitable for a DGR and it is irrelevant that the M1, M14, M16, & AK47 which were designed for hunting men that can shoot back are all PF actions.
8. 95 deg F in Africa is different than 95 deg F in TX or CA and that is why you must worry about ammunition temperature in Africa (even though most safaris take place in winter) but not in TX or in CA.
9. The size of a ding in a gun's finish doesn't matter, what matters is whether it’s a safe ding or not.
10. 1 in a row is a trend, 2 in a row is statistically significant, and 3 in a row is an irrefutable fact.
11. Never buy a WSM or RCM cartridge for a safari rifle or your go to rifle in the USA because if they lose your ammo you can't find replacement ammo but don't worry 280 Rem, 338-06, 35 Whelen, and all Weatherby cartridges abound in Africa and back country stores.
12. A well hit animal can run 75 yds. in the open and suddenly drop with no initial blood trail, but the one I shot from 200 yds. away that ran 10 yds. and disappeared into a thicket and was not found was lost because the bullet penciled thru. I am 100% certain of this even though I have no physical evidence.
13. A 300 Win Mag is a 500 yard elk cartridge but a 308 Win is not a 300 yard elk cartridge even though the same bullet is travelling at the same velocity at those respective distances.
 
Posts: 10181 | Location: Loving retirement in Boise, ID | Registered: 16 December 2003Reply With Quote
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popcornOne of the old Speer manuals dealt with this. Can't remember which one but I'll bet someone will find it. beerroger


Old age is a high price to pay for maturity!!! Some never pay and some pay and never reap the reward. Wisdom comes with age! Sometimes age comes alone..
 
Posts: 10226 | Location: Temple City CA | Registered: 29 April 2003Reply With Quote
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I myself would use the same twist rate on both, probably 1-10. The 10% rpm reduction(3000fps to 2700fps) I don't believe will effect most bullets, unless you go below the magic number that is required by heavier bullets, all bullets for that matter. All bullets have a "min." and a "max" RPM. Spin too fast they come apart, too slow and they won't stabilize. The good news is it is a fairly broad range for most bullets. I like to shoot the 'heavy for caliber' bullets so I go for the faster twist rates. In .30 cal. I like to shoot 210 gr. Bergers, 208 gr. A-Max and 200 gr. SMK. A 1-9 twist would be better for them, but you wouldn't be able to go down to say, 125 grainers for varmits,maybe not even 150 gr. I am building a .220 Swift at the moment with a 1-8 twist so I can shoot 80 gr. bullets. The 50 grainers pushed to 4200fps, 378,000 RPM out of this gun will probably never reach the target, 378,000 RPM is just too fast for most .22 bullets.

The answer to your question....Yes, it does.


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Posts: 654 | Location: Denver, Iowa | Registered: 10 June 2009Reply With Quote
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Bullet stability is determined by the projectile's rpm, not "x" number of turns in so many inches/feet/whatever. So technically yes, bullet velocity has a direct effect on bullet stability. My .222 Rem with a 1:14 twist will not stabilize any of the 55 grain plastic tipped bullets. My buddy's .22-250 with the same twist will stabilize these bullets and even longer (and usually heavier) ones. In your example however, a 1:10 twist in either chambering will do just fine.


Praise be to the Lord, my rock, who trains my hands for war, my fingers for battle.
 
Posts: 427 | Location: Clarkston, MI | Registered: 06 February 2006Reply With Quote
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In the larger bullets, it doesn't seem to matter as much, ie 180 gr 308 stabilize in 30-06, 300 Win mag and 30-378 with 1 in 10. But, a 50 gr 224 round has different twist rates for 223 and 22-250 (1-12 and 1-14 respectively).

John
 
Posts: 1343 | Location: Northern California | Registered: 15 January 2006Reply With Quote
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If you are building a match precision rifle...yes, you might consider different rates of twist.

If you want to use non standard bullet weights for the calibre then yes, a change in twist rate might be worth it.- eg my Bruno 7x57 doesn't shoot any bullets lighter than 160gn particularly accurately. If I wanted to shoot say 140grn Noslers from a 7x57 You would be best advised to pick something other than 1:8,5 (and yes- at that rate of twist they are stable...just not accurate!)

Does stability have any hunting considerations? Only on elephant guns. Other than that, if it stabilises the bullet enough to be accurate- who cares! I have seen understabilised bullets used on ele 350grn .375's from old Parker Hale 1:16 twist barrels- that is not a combination for sucess....
 
Posts: 3026 | Location: Zimbabwe | Registered: 23 July 2003Reply With Quote
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I believe it depends what type bullets and weight one is using and the speed
If you say had an 300mag. 1:9 to stabilize the heavyweights, you may overstabilize the lighter much faster cupcores, however if you ran a monometal like an 130hv its no so much a concern.
when I asked about running 130 monometals in 300weatherby,This was Gerards from GSC, responce;
"High stability factors accentuate bullet imbalance and target shooters tend to choose the slowest twist that allows stable flight with jackted lead core bullets. Turned copper monos do not have this potential imbalance problem and high stability factors will not affect accuracy."

Gerard mentioned using 1:8 twist for 308win.
 
Posts: 9434 | Location: Here & There- | Registered: 14 May 2008Reply With Quote
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It is important to know that you can not fix a bullet length / twist rate mismatch with speed.

Take a 160gr turned mono hollow point fired froma 1:10" twist.

At a mv of 3200fps, it has a stability factor of 1.6. At a mv of 2600fps, the stability factor is 1.57. To get to a stability factor of 1.6 at 2600fps mv, requires a twist of 1:9.9"

Both bullets will increase in stability factor as they go downrange and when the factor exceeds 3, it doesn't really matter what it is as the difference it makes on impact is negligible. Far more important will be the difference the impact speed will have on penetration and wound channel volume.
 
Posts: 2848 | Registered: 12 August 2002Reply With Quote
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Yes, as velocity increases the rate-of-twist required for stabilizing a given bullet decreases. The difference, however, is relatively small.

For many years Weatherby used a 1-12" twist in its .300 barrels on the theory that the speed of the cartridge offset the need for a faster twist. That is true to some small degree, and Weatherby got by with it so long as spitzers no more than 180 grains were used.

On the other hand, slower cartridges in a given caliber are frequently fitted with a slower twist since it is assumed they will be used with lighter (shorter) bullets. Hence the 1-12" twist for the .30-30 with its blunt 150-170 grain bullets; and 1-10 for the .300 Winchester which frequently is used to shoot pointy bullets of 180 grains or more.

Juggernaut's example of a .222 vs. a .22-250 with the same twist handling the same 55 grain bullet differently (although not apples to apples since such a test would need to use the same barrel) is a good example of speed offsetting slow twist rate.
 
Posts: 13277 | Location: Henly, TX, USA | Registered: 04 April 2001Reply With Quote
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I always though it did. But I really don't know.
 
Posts: 2209 | Location: Delaware | Registered: 20 December 2002Reply With Quote
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So I believe the concensus is yes it does. But my limited experience has shown that it is much more critical in smaller caliber firearms. I have shot 235-350gr in a 375 with no stability problems (Win M70 std twist). I have shot 110-200gr in 308 wirh no stability problems (Rem M700 std twist). But my 223 needed a rebarrel to a faster twist to shoot anything over 45gr (went from 1 in 14 to 1 in 9). So is twist rate more critical in smaller calibers?


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The value of a trophy is computed directly in terms of personal investment in its acquisition. Robert Ruark
 
Posts: 3831 | Location: Cave Creek, AZ | Registered: 09 August 2001Reply With Quote
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Using the same bullet for each of the calibers below, here is what happens.

Cal --- s/f ---- m/v -- twist
223 - 1.18 - 2500 - 1:14
223 - 1.60 - 2500 - 1:12
223 - 1.21 - 3500 - 1:14
223 - 1.65 - 3500 - 1:12

308 - 1.05 - 2000 - 1:12
308 - 1.52 - 2000 - 1:10
308 - 1.13 - 3000 - 1:12
308 - 1.63 - 3000 - 1:10

375 - 1.10 - 2000 - 1:14
375 - 1.50 - 2000 - 1:12
375 - 1.15 - 3000 - 1:14
375 - 1.57 - 3000 - 1:12

500 - 1.85 - 1500 - 1:16
500 - 2.41 - 1500 - 1:14
500 - 2.13 - 2500 - 1:16
500 - 2.78 - 2500 - 1:14

So, none of the combinations above will tumble or produce oval holes on paper. All will give stable flight. Observing this stable flight and round holes will sooth us into believing that all is well.....until we shoot an animal. Then the difference becomes apparent.
 
Posts: 2848 | Registered: 12 August 2002Reply With Quote
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So, my conclusion is that the difference is going to be immaterail if we are talkign about 300-400 fps which is the typical spread of cartriddges with in any given caliber.

For example, if I am going to build a 30 caliber rifle, the bigger determin factoring is going to be what bullet weight I want to shoot versus the velocity I am going to shoot it at.

I am not going to be able to make up for two slow a twist rate by launching a bullet 400 fps faster.

Meaning it would be a fools errand to build a 300 RUM on a 1:12 twist because I can launch the bulltet at 3000 fps but I better build the 308 win on a 1:10 becuase it is only going 2600.


Mike

Legistine actu quod scripsi?

Never under estimate the internet community's ability to reply to your post with their personal rant about their tangentially related, single occurrence issue.




What I have learned on AR, since 2001:
1. The proper answer to: Where is the best place in town to get a steak dinner? is…You should go to Mel's Diner and get the fried chicken.
2. Big game animals can tell the difference between .015 of an inch in diameter, 15 grains of bullet weight, and 150 fps.
3. There is a difference in the performance of two identical projectiles launched at the same velocity if they came from different cartridges.
4. While a double rifle is the perfect DGR, every 375HH bolt gun needs to be modified to carry at least 5 down.
5. While a floor plate and detachable box magazine both use a mechanical latch, only the floor plate latch is reliable. Disregard the fact that every modern military rifle uses a detachable box magazine.
6. The Remington 700 is unreliable regardless of the fact it is the basis of the USMC M40 sniper rifle for 40+ years with no changes to the receiver or extractor and is the choice of more military and law enforcement sniper units than any other rifle.
7. PF actions are not suitable for a DGR and it is irrelevant that the M1, M14, M16, & AK47 which were designed for hunting men that can shoot back are all PF actions.
8. 95 deg F in Africa is different than 95 deg F in TX or CA and that is why you must worry about ammunition temperature in Africa (even though most safaris take place in winter) but not in TX or in CA.
9. The size of a ding in a gun's finish doesn't matter, what matters is whether it’s a safe ding or not.
10. 1 in a row is a trend, 2 in a row is statistically significant, and 3 in a row is an irrefutable fact.
11. Never buy a WSM or RCM cartridge for a safari rifle or your go to rifle in the USA because if they lose your ammo you can't find replacement ammo but don't worry 280 Rem, 338-06, 35 Whelen, and all Weatherby cartridges abound in Africa and back country stores.
12. A well hit animal can run 75 yds. in the open and suddenly drop with no initial blood trail, but the one I shot from 200 yds. away that ran 10 yds. and disappeared into a thicket and was not found was lost because the bullet penciled thru. I am 100% certain of this even though I have no physical evidence.
13. A 300 Win Mag is a 500 yard elk cartridge but a 308 Win is not a 300 yard elk cartridge even though the same bullet is travelling at the same velocity at those respective distances.
 
Posts: 10181 | Location: Loving retirement in Boise, ID | Registered: 16 December 2003Reply With Quote
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Hello Ganyana,

I have been loading the 7x57 for the past 30 years. Perhaps the inaccuacy problem with the long throated BRNO (and most of the european 7x67s) is just its long throat rather than the twist. I have experienced the same wih mine.

Best Wishes!

PH
 
Posts: 382 | Registered: 17 March 2006Reply With Quote
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Patagon - you are right, the long throat is a (large part of the ) problem, but also that the bullets take a long time to 'go to sleep' in target shooting terms with an over stabilised bullet.
 
Posts: 3026 | Location: Zimbabwe | Registered: 23 July 2003Reply With Quote
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Apparently, the twist rate versus MV is so small that less twist is required at lower velocity but more twist is required near the trans-sonic zone. The minimum required twist rate is not constant over a wide velocity range, nor is the relationship linear. Then we have a 22 hornet able to stabilize a 60gr spire point with a 1-in-16 twist! (Accurate too).

Have a look at JBM.
This is just a random example. The table does not copy properly. The second to last column is the twist rate.
quote:
Calculated Table
Mach Muzz Vel CD CD CD CD CD CD BC Form Twist Stability
Number (ft/s) Nose Boattail Base Band Skin Total (G1) Factor (in) (>1.5)
0.500 558.2 0.000 0.000 0.043 0.000 0.069 0.112 0.285 0.550 6.1 1.1
0.600 669.9 0.000 0.000 0.046 0.000 0.065 0.111 0.287 0.546 6.1 1.1
0.700 781.5 0.000 0.000 0.049 0.000 0.062 0.111 0.304 0.515 6.0 1.1
0.800 893.2 0.000 0.000 0.053 0.000 0.060 0.112 0.355 0.441 5.8 1.0
0.850 949.0 0.000 0.000 0.055 0.000 0.058 0.113 0.402 0.390 5.7 1.0
0.900 1004.8 0.000 0.004 0.056 0.000 0.057 0.118 0.454 0.345 5.4 0.9
0.925 1032.7 0.013 0.008 0.057 0.000 0.057 0.135 0.433 0.362 5.2 0.8
0.950 1060.6 0.027 0.016 0.058 0.000 0.056 0.158 0.405 0.386 4.9 0.7
0.975 1088.5 0.039 0.044 0.059 0.000 0.056 0.198 0.351 0.446 4.7 0.7
1.000 1116.4 0.051 0.090 0.084 0.000 0.055 0.281 0.268 0.584 5.7 1.0
1.100 1228.1 0.119 0.056 0.084 0.000 0.053 0.313 0.295 0.531 5.6 0.9
1.200 1339.7 0.106 0.075 0.083 0.000 0.052 0.316 0.317 0.494 5.8 1.0
1.300 1451.4 0.099 0.077 0.082 0.000 0.050 0.308 0.335 0.468 6.1 1.1
1.400 1563.0 0.093 0.074 0.081 0.000 0.049 0.297 0.349 0.448 6.2 1.2
1.500 1674.7 0.090 0.070 0.080 0.000 0.047 0.286 0.360 0.435 6.4 1.2
1.600 1786.3 0.086 0.065 0.078 0.000 0.046 0.276 0.367 0.427 6.5 1.3
1.700 1898.0 0.084 0.062 0.077 0.000 0.045 0.267 0.372 0.420 6.5 1.3
1.800 2009.6 0.082 0.058 0.075 0.000 0.044 0.258 0.377 0.416 6.6 1.3
2.000 2232.9 0.078 0.052 0.071 0.000 0.042 0.242 0.383 0.408 6.7 1.4
2.200 2456.2 0.075 0.047 0.066 0.000 0.040 0.228 0.390 0.401 6.8 1.4
2.500 2791.1 0.071 0.041 0.060 0.000 0.037 0.209 0.404 0.388 6.9 1.5
3.000 3349.3 0.066 0.034 0.050 0.000 0.033 0.183 0.439 0.356 7.0 1.5
3.500 3907.6 0.063 0.028 0.041 0.000 0.030 0.162 0.488 0.321 7.1 1.6
4.000 4465.8 0.060 0.023 0.034 0.000 0.028 0.145 0.541 0.290 7.2 1.6
4.500 5024.0 0.058 0.020 0.028 0.000 0.026 0.131 0.595 0.263 7.2 1.6

Error? 05/08/09 11:29, JBM/jbmdrag



Regards
303Guy
 
Posts: 2518 | Location: New Zealand | Registered: 02 October 2007Reply With Quote
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Velocity does affect stability. But not nearly as much as twist does.


"Bitte, trinks du nicht das Wasser. Dahin haben die Kuhen gesheissen."
 
Posts: 4386 | Location: New Woodstock, Madison County, Central NY | Registered: 04 January 2005Reply With Quote
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