Reply With QuoteWhat are you having it chambered for?
Hey all,
I'm getting ready to order my barrel from Apache Barrels. Good price, high quality barrel it seems.
I want a barrel that could push 115s if i choose to shoot them. However, I also want flexibility.
If i get a barrel with a twist of 1:7, am I limiting myself to any other bullets? Will other weights work fine, as well?
If i go 1:8, i will not be able to shoot 115s at all.
So, is there a con to going with a 1:7?
What are you having it chambered for?
+1,
Without the chamber we can't say anything.
Next is "115gr bullets" , this isn't very helpful by itself. Bullet weight doesn't mean much, bullet length is what is critical. Stabilisation is about length.
Unless you are talking 5,500+ fps, velocity doesn't harm bullets. RPM is what will destroy them. Most match bullets RPM limit is @ 290,000 - 320,000 RPM. Which bullet is dependant, as well your specific barrel.
I'm a firm believer in the theory that if it bleeds, I can kill it.
I would guess 6mm of some sort. 1:7 is my suggestion guessing you would be looking towards 115DTACS or 115VLDs. I don't know too many other 115gr bullets in the 6mm realm. H100V worked real well in my 243 with the DTACS though. I did print a 1.438" group at 415yds with that combination.
Oh man...I really though I put that on my post...
243 WIN is what I'm having it chambered in.
Here's some more specs for your notes:
27" 1:7 twist XCaliber
243 Win spun by AGW
Load
hornady 243 brass
CCI 200 primer
40.0grs of H100V
115DTAC
I was getting 2950fps with that load.
I've since switched to an 8 twist and 105 class bullets. The AMAX has been good to me at 3050-3100fps from a 26" barrel.
Last edited by LoneWolf; 02-02-2016 at 01:26 AM.
Right.... But still haven't said WHICH bullet.... I'll assume you don't care about Barnes 115gr round nose.Originally Posted by idunham
Berger's - 1.365"
DTAC - 1.290"
Precision Ballistics - 1.330"
A muzzle velocity of 2500fps
7-twist - stability factor 1.526. Very good
8-twist - 1.168, marginal. EXCEPT DTAC, stability good 1.379
So bump speed to 3k
8-twist - stability factor 1.241, marginal.
Now remember that velocity decay happens rapidly, whereas rotational does not. So the 8 Twist doesn't automatically mean unstable.
Now your flexibility math. MV * 720 / Twist = RPM
So let's assume super smooth barrel gives optimal results.
Nominal RPM limit on modern match/Varmint bullets:
290,000 * 8 / 720 = 3,222 fps max
290,000 *7 / 720 = 2,819 fps max
So. YES, you can stabilize A 115gr with an 8-Twist, just use the correct bullet. No, you don't get to shoot 4,000 fps Varmint bullets. Just depends upon what you want.
If you buy a Ferrari, you don't complain there is no room for groceries
I'm a firm believer in the theory that if it bleeds, I can kill it.
So, If i got a 1:8 twist, I should be able to shoot everything up to 115gr (In most cases, assuming i don't use Bergers round nose?).Right.... But still haven't said WHICH bullet.... I'll assume you don't care about Barnes 115gr round nose.
Berger's - 1.365"
DTAC - 1.290"
Precision Ballistics - 1.330"
A muzzle velocity of 2500fps
7-twist - stability factor 1.526. Very good
8-twist - 1.168, marginal. EXCEPT DTAC, stability good 1.379
So bump speed to 3k
8-twist - stability factor 1.241, marginal.
Now remember that velocity decay happens rapidly, whereas rotational does not. So the 8 Twist doesn't automatically mean unstable.
Now your flexibility math. MV * 720 / Twist = RPM
So let's assume super smooth barrel gives optimal results.
Nominal RPM limit on modern match/Varmint bullets:
290,000 * 8 / 720 = 3,222 fps max
290,000 *7 / 720 = 2,819 fps max
So. YES, you can stabilize A 115gr with an 8-Twist, just use the correct bullet. No, you don't get to shoot 4,000 fps Varmint bullets. Just depends upon what you want.
If you buy a Ferrari, you don't complain there is no room for groceries
I'm trying to figure out if I should go with a 1:8 twist, will i regret not going with a 1:7 twist.
.... What???!!
Berger doesn't make a 115 RN... I said BARNES as a joke.... You aren't getting this, so I'll explain simply again.
You need to stop talking about bullet weights, as a thing.
Look at my previous post again. The same weight-class, same match style bullets, BIG difference in length.
Twist rate is for stability.
Stability is for a LENGTH, weight doesn't matter.
Weight is for choosing a date, or worrying about when they tone for a medical assist...
Here:
http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi
Length look-ups are on the left margin.
Again,
These fast twists limit how fast you can push bullets.
So bullet dependant, and depending upon how smooth your barrel is, here are the speed limits before the RPM destroys them.
8-twist - @ 3,200
7-twist - @ 2,800
Last edited by darkker; 02-02-2016 at 09:22 AM.
I'm a firm believer in the theory that if it bleeds, I can kill it.
My RPR is a 1:7.7 twist.
I've had good luck with the 115gr DTACs, and the 115gr VLDs have showed some promise as well, but I haven't experimented as much with the latter. Both definitely prefer the faster twist barrel.
[I]"In the end, run what 'ya brung because it's better than nothing and don't give two ****s what some interwebs chat board guy says about your rig."[/I]
I have a very large pile of barrels in 8 twist from 6BR and 6Dasher all the way to 6mm-06 and can push a 115 over 3300 fps.
The earlier Bergers blew up from heat allowing the core to melt and the thin jacket not holding up. The sloution was thicker jackets on the target bullets usually fired from very long barrels where frictional heat becomes an issue.
In a 6mm-06 with a typical 30 inch barrel 57 grains of H1000 and using Lapua 30-06 brass gives me 3433 fps using the 103-108 grain bullets and best accuracy.
If I step up to the heavier bullets like the DTAC or Berger I can achieve a little over 3300 fps before I see pressure but best accuracy is at 3200 fps and giving the 103-108 bullets a ballistics edge.
I wouldn't go with a straight 7 twist but as previously posted a 7.7 or 7.8 twist if you absolutely have to shoot the 115's.
Rotational forces have very little to do with bullet blow ups as they rarely exceed 20,000 psi.
Ok, right on, that makes sense to me.
You have the right end result, but the wrong info.
Until you exceed around 5,500 fps velocity, air friction doesn't catastrophically damage bullets. What makes they pop, is Centripidal force over coming centrifugal force. A thicker jacket will hold things together at higher rotational speeds, true. Back to specific bullet discussions and not generalities. I called all the majors a while back and asked for RPM limits on bullets.
These numbers are HIGHLY dependant upon barrel smoothness. Not all jackets can take the same stresses. Cooking bullets in a hot chamber doesn't melt the core, but damages the integrity of the jacket.
Hornady - SXSP - 240,000 rpm. A, V, SP = 290,000 rpm
Nosler/Sierra - 320,000 rpm. I can't say the older thin jacketed name, but it was 240-260,000rpm
The math again, if you want it: MV * 720 / Twist = RPM
This is a slippery-slope in that, while higher RPM can gain a slight edge in BC; it also exacerbates ANY bit of concentricity issues. That is where the notion of "over-stabilized" comes from.
115 DTAC's will happily stabilize in an 8-twist.
I'm a firm believer in the theory that if it bleeds, I can kill it.
I don't think I ever mentioned air friction at all.
The problem Berger Bullets were suffering was do to the thin jackets not being able to withstand the acceleration forces which run over 100,000 G,s and not rotational forces.
In laymens terms thin jackets don't like long rough barrels and twist rate doesn't play much of a role in bullet failures.
The whole 4-5 pages can be seen on Benchrest Central with Eric Stecker reporting the MIT results. It is in the F-Class forum if my memory is any good.
Last edited by Lynn; 02-02-2016 at 08:41 PM. Reason: Spelling error
I figured most wouldn't be able to look up the actual results as posted by Bergers Eric Stecker so here you go.
http://benchrest.com/archive/index.php/t-49336.html
Yes Lynn, re-read what it all says.
I agree he talks about a melted core, secondary failure is high RPM. We aren't talking factory twist rates, so RPM becomes a very significant concern.
And he reiterates near the end of his post from 7:01pm. That the loads in question were generating 254,000 RPM, which as he said "was well within acceptable limits". This also corresponds with what I have said, and been told by the bullet makers.
As HBC explains just below that post, in fact jacket damage is what caused the failure, not a melty core. Damaged jackets under high rotation stress cause a yard sale.
As Eric says, there are many things that play into it. In high RPM, high volume shooting causes the light jacket, AKA VLD hunting line, to be an un-appropriate choice.
Last edited by darkker; 02-02-2016 at 10:23 PM.
I'm a firm believer in the theory that if it bleeds, I can kill it.
I have read it many many times as I am the Lynn Dragoman Henry the bullet God Child's refers to in his post.
A typical 30 caliber 200 grain bullet at 3000 fps will have around 127,000 G,s during it acceleration down a 30 inch barrel but less than 30,000 pounds of rotational force.
If rotational force was tearing the bullets apart they would also be collapsing from the much higher forces associated with there acceleration.
And that was what happened to the original 338 OTM Hybrids. The BC was originally over 0.900 but nobody could get there claimed BC number to match at longer distances. When Bryan Litz looked into it the ogives were collapsing.
Now we have either 0.818 or 0.822 as the bc instead of 0.950 like the original version.
Lynn,
If RPM is not the destroyer, them why don't 22-250's Swifts, WSSM's ALL just use 9-twists? The answer is because the RPM will destroy them. You only use right twists to stabilize long bullets, which are fired slower thusly don't have the same RPM.
As to your 338 example.
Litz is constantly changing BC numbers on his bullets. Now because I'm not familiar with the issue in question, I'll play along. Assume the ogive was collapsing. This is a completely side issue to RPM. If in the thread link, the jacket alone was being destroyed by G's; then Berger would not have ever kept the original jacket. Which is what the hunting line is.
Last edited by darkker; 02-03-2016 at 11:49 AM.
I'm a firm believer in the theory that if it bleeds, I can kill it.
The hunting line is what most of the Long-range Benchrest shooters use in there 600/1000 yard chamberings because the jackets are more concentric.
If you are a Competitive Shooter you only switch to the target bullets if you are experiencing failures.
Friction is what caused the failures not rotational forces.
Bullet length all else the same determines twist rate not velocity.
If your gyroscopic stability is 1.5 it doesn't matter what velocity your shooting because a 1.5 GS means the bullet is stable.
The only time twist rate comes into play is guys with a GS of 1.2 shooting 1000 yards and maximum loads in a very long barreled 308.
They are already on the edge and small variances can mean big trouble quickly.
The guys winning Benchrest matches at 1000 yards with the 6 Dasher are using 8.3-8.7 twist barrels and 103-108 grain bullets. When asked about there twist most just say 8 twist to avoid confusion.
This is absolute lunacy.
1) Maybe they do use them, but it IS NOT because of jacket uniformity. They would use them because of jacket damage in high heat, rapid fire situations Call Berger and ask them that, or better yet read that it isn't true in their FAQ.
http://www.bergerbullets.com/informa...ked-questions/
None of this has anything to do with your false claims of G forces by the way.
2) That is also not true, but the WHY they would switch is perfectly reasonable. Again this is a deflection from your G force claims, and if they were killed by G forces, they wouldn't stay with these bullets as you claim. So which is it? You can't have both sides of the argument.
3) Friction is what damages the jacket, on that we both have always agreed. Once that bullet is out of the barrel, is where, in an attempt to keep this nonsense relative to the OP, in a high RPM situation, will then destroy the bullet. NOT the G forces.
4) I'm not sure what this is supposed to mean. I agree that bullet length is what you should consider to choose a twist rate. HOWEVER, ignoring velocity simply shows you don't understand what you are talking about. So here is your formula, AGAIN: MV * 720 / Twist = RPM.
5) Again, Velocity is CRITICAL to your stability factor, as it DIRECTLY affects the RPM. The RPM is in fact what gives you stability. Look at the formula, again, and do the math. MV = Muzzle Velocity. Without a velocity, there is zero RPM. Only a useless twist rate, and a cartridge in a chamber that you can't fire.
6) Again false. Why did the original 6mm Remington Fail? Because it had a slow twist to ensure that no varmint bullets would be destroyed. Thus it could not handle anything heavy enough to hunt game with, where the 243 had a twist that generally worked with several bullets.
Or more recently look at the 223 WSSM cartridge. If your claim of velocity not mattering or G forces caused the damage, then they would have used a 9-twist. Why didn't they? Because the velocity possible in that cartridge would impose an RPM that would destroy anything remotely useful for varmint hunting.
I'm a firm believer in the theory that if it bleeds, I can kill it.
I don't want to burst your bubble but the bullets are actually damaged in the barrel and generally blow up within 60-80 yards downrange or fail to reach the target as Eric Stecker likes to put it.
As to the lunacy I won the 2010 NBRSA 1000 Yard Benchrest Nationals with that lunacy and jacket concentricity is indeed better with the thinner jackets period. They are harder to make but better.
And Eric knows me so don't take my word on it give him a call I already know what he will tell you.
As to your twist rate ?please read my post again.
It should read that if your gyroscopic stability is 1.5 the velocity doesn't matter.
If your shooting a 6BR at 2850 fps AND the twist rate gives you a GS of 1.5 you are good to go.
If your shooting a 6mm-06 Ackley Improved at 3500 fps AND the twist rate gives you a GS of 1.5 you are good to go.
That is what I actually said.
What I didn't say was to shoot 55 grain bullets out of a 7 twist barrel at maximum velocity in a 6mm-06 Ackley Improved as the GS would be too high.
Last edited by Lynn; 02-03-2016 at 10:47 PM.
http://bulletin.accurateshooter.com/...-ogive-bullet/
If you look at the numbers in the enclosed link you will find the BC number to be 0.950 not 0.818 or 0.822 like it is on the boxes of today.
The reason for the huge variation was due to "ogive slumping" and Eric or Bryan can explain its causes to you or you can search it on Google where it is also clearly explained.
Good Luck with your future shooting.
Lynn
Lynn beware.... arguing with Darker is futile.
I am not arguing here with anyone as it wastes time. I am here to share and to get some answers.
I just looked up the earlier post.
Here are a few interesting facts about, say a
30 cal. 1000 yard load that shoots a bullet having a maximum acceleration
that makes the acceleration of a fuel dragster pale by an order of many
magnitudes:
First let me give you the true definition of
acceleration, "a": a = dv/dt, where dv in an infestimally small change in
veloctiy and dt is an infestimally small change in time corresponding to
the change in velocity and occurs at a point in time. I
realize that is not too colorful but you can use that equation to estimate the
average acceleration of a fuel dragster. That is a = (333
mph*88f/s/60 mph)/4.441 sec = 109.97 f/sec2 or 109.97 ft/sec2/32.17405 ft/sec2
= 3.41 g's. Acceleration defined in words is the rate of change in
velocity with respect to the accompanying change in time.
Now for the 30 cal mag. load shooting a 220 grain
MK at a muzzle velocity of 3002 f/s with a barrel time of 0.001711
seconds:
The average bullet acceleration in the
barrel is 54,532 g's (That is the fuel dragester's average
acceleration increased by a multiple of 15,991 times.)
The maximum acceleration, which occurs near max.
chamber pressure, is 126,849 g's (Under that amount of acceleration, a
free standing column of pure lead taller than 0.077" will began to collapse upon
itself.)
Power is the rate that energy is transmitted.
One Horsepower is defined as delivering or transmitting 550 ft-lbf in one
second. Thus one can calculate the average rate that energy is delivered
to the 220 grain VLD thus:
(3002)^2*220/450436.7/0.001711sec/(550
ft-lbf/sec/HP) = 4677 Horspower That is a lot of Horsepower for
such a small bore but true, although the delivery time is very short for
the single stroke rifle "engine" and the peak Horsepower would likely
be much higher but I would have to modify my internal ballistics program to
estimate the peak HP. Peak energy delivery rate to the bullet, or
peak HP, would likely occur well past maximum chamber pressure.
If the 300 Mag. were fired, such that the bullet
was exiting the cartridge case and entering the barrel bore as the
fule dragster was about 80 yards from the finish line, the bullet would reach
the finish line first.
If the math is correct I was in error earlier by 11 G's
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