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Ballistic Stabilty Calculator
Discussion regarding the reloading of ammunition and tuning of loads for accuracy
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Ominivision1
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PostPosted: Mon Jun 20, 2011 10:41 am    Post subject: Ballistic Stabilty Calculator Reply with quote

Getting ready to do some reloading for the /06 and was doing some checking at manufacturers web sites and noticed quite a difference on the bullets I have been using (good price) which are the Remington 150gr psp. What caught my attention at Noslers web site was the bullet length for their offering, was at 1.280" vs what I was loading with the Remington at 1.075".

Now thats .205" difference. So I fired up the ballistic stability calculator and ran my loads through it and sure enough, it appears that the Remington bullet is over stabilized and the Nosler is in the ballpark. Has any one else used this calculator before you made your bullet purchase?

The gun is a M700 and always shot 2 1/2" to 3" groups at 150 yards with them Remington 150gr bullets. Since I had bought 700 of these bullets I never gave it a thought to shop around until my supply ran low.



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gelandangan
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PostPosted: Mon Jun 20, 2011 2:59 pm    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

Thats one of the time where I reckon changing muzzle velocity would make difference.
Vary the muzzle velocity and you can tune the stability factor.
Although I admit the differences might be very difficult to nullify, it might be a possible outcome.

Shorter projectiles requires less spin to stabilize.
And spin is a function of barrel twist and velocity.
You cannot change barrel twist unless you change barrel, so that left you with velocity to play with.

I reckon lowering your velocity will bring you better stabilization for shorter projectiles.

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PaulS
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PostPosted: Mon Jun 20, 2011 5:53 pm    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

As far as my experience goes you have to go way short to make the bullet "over-stabilized". I shoot 158 grain JHC from a 358 Win. with 10 " twist - to average groups of .33" at 100 yards at 2700 fps.

That is not overstabilized in my book but it should shoot best from a 18 twist according to the tables.

In my 30-06 I have successfully fired 110 gr HP all the way to 200 grain RN with a 10 twist. All shoot under MOA.

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slimjim
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PostPosted: Mon Jun 20, 2011 8:30 pm    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

I looked at your numbers and scratched my head as the SF seems abnormally high for a 150gr .308 bullet. I ran it through Don Miller's stability equation and got 3.1 SF. You might check some other stability formulas for comparison.

bulletin.accurateshoot...stability/

I agree with PaulS. I don't think you have a real problem. If your spin rate was too high, the lead-core bullet could self distruct but you are not at that point. You may find your loads with lower SF might be more accurate.

You can find some interesting information on bullets and stability at GS Custom bullets. They recommend SF greater than 1.5 in some hunting situations.

gscustom.co.za/

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Elvis
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PostPosted: Mon Jun 20, 2011 10:30 pm    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

Omni get ahold of some sample pack projectiles they are not too expensive and you get to play around with different options without being stuck with 675 projectiles your gun doesnt like.
what sort of group do you get with factory loads???
the only loads Ive ever used in my .270 that grouped like that were hornady 110grn fbhps at around 3000fps. good for wallabies if you hit em they dropped very explosive so maybe going too fast.
Ive loaded 06 for a buddy using 125grn taipans and they group ok.
the best thing about those sample packs is being able to get top line projectiles at a small cost.

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Ominivision1
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PostPosted: Mon Jun 20, 2011 11:46 pm    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

This rifle does not shoot to bad, its just that I stumbled across these figures and was a astonished when running the numbers through the calculator.

gelandangan: yup, when working up different loads with this bullet, I found out the best accuracy is at 200-250fps slower then published factory loads.

Paul: When loading for 180gr nosler spitzer, my groups are .50 at 150 yards. when loaded to 2650fps which are better than the 150gr. I just ordered the 165gr and see how it groups compared to the 150gr.

Elvis: this gun has never seen a factory load, I did order 100 of 165gr and will do some load developing with these noslers and see what happens.

Slim: yup, they have a couple of different calculators out there and with the miller formula, the values are much lower which is good.

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Elvis
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PostPosted: Tue Jun 21, 2011 1:39 am    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

that 180grn load sounds great Omni you could be on to something with bullet length etc being the key to making her shoot. if your 165s arent flash keep trying you will find the magic bullet forsure.

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slimjim
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PostPosted: Tue Jun 21, 2011 2:55 am    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

Its common to find production .30-cal rifles with twist rates of 1:10, 1:11, and 1:12. When looking at bullet stability across those twist rates, I was surprised how much of a stability factor a .30-06 or .308 has with even a 1:12 twist using today's common hunting bullets, e.g., 130, 150, 165, and 180gr. Also, how much more stability a .30-06 has compared to a .270 with a 1:10 twist. The .30-06 with a 1:10 twist has a stability factor of 1.3 with 240gr Sierra Match Kings (1.591") on a cold day, 0 deg F. My .270 doesn't have that high of a stability factor with some of my 130gr bullets.

BTW, below is a reference website for bullet length.

www.jbmballistics.com/...gths.shtml

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Last edited by slimjim on Tue Jun 21, 2011 6:05 am; edited 1 time in total
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Ominivision1
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PostPosted: Tue Jun 21, 2011 3:25 am    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

Yup, that jmballistics site is pretty good, I submitted specs for some barnes and nosler bullets to him last fall. Hopefully with people helping him out with the specs, he can get his database completed.

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chambered221
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PostPosted: Tue Jun 21, 2011 9:10 am    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

I wouldn't let them figures keep you from using 150gr bullets if that's all you want or need !!!

The group size your getting is more about the bullet your using.........not stability factors.

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Ominivision1
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PostPosted: Tue Jun 21, 2011 10:22 am    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

I agree Chambered, I have also loaded up 125gr Nosler spitzer and even then the formulas tell me the bullet is over stabilized. But yet I take these loads to the range with imr4831 with 57grs and its a tack driver with this load. I can put groups at 1" at 100 yards doing my part.

Like I said in an earlier post, the 180gr nosler will do better then the 150gr rem bullets and so will the 125gr nosler bullets. As soon as the new bullets get here, I will load them up and get back here with a post and pictures. And like Slim said earlier that some of the calculations showed the .270 with the 130gr had less stability then a 30/06 with a 240gr bullet. Shocked

I also own a .270 and it has always been a tack driver with the 130gr loads, sometimes what they come up with on these calculators is very different then reality.

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Pumpkinslinger
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PostPosted: Tue Jun 21, 2011 1:22 pm    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

I think we've discussed this before and I don't think you can "overstabilize" a rifle bullet. This would only be a problem with artillery fired at a high angle. I pick a bullet based on two factors; terminal performance and accuracy.

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Elvis
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PostPosted: Tue Jun 21, 2011 1:50 pm    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

pumpkinslinger Im sure you are right on the overstablilize thing its been thrashed before. If I get the theory correct overstablilize would be when it spins too fast and the structural integraty is comprimized. (hows that for a sentence of wheelbarrow words!!!) If you round things off abit for ease of calculations a projectile doing 3000fps fired through 1 in 12 rifling is rotating 3000 times per secound which is 180,000 rpm. so its no wonder we run into issues at times.

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Pumpkinslinger
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PostPosted: Tue Jun 21, 2011 6:13 pm    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

Elvis, "over stabilized" and spinning a bullet so fast that it comes apart are obviously both related to the rotational speed, which is a product of the muzzle velocity and barrel twist rate, but they are different issues. Lets say we take two different .224" 45 grain bullets, one a light jacketed varmint bullet and the other a solid copper, and fired both in a .22-250 with a 1-in-9" twist. They would both be pretty equally "over stabilized" according to the "stability factor". The solid bullet would stay together though, while the thin skinned varmint bullet would likely come apart when it exits the muzzle.

Sorry, I'm trying not to beat a dead horse but I learned long ago that you have to really understand a problem before you can come up with a real solution. Over the years I've seen a lot of "gun shop gossip" muddy the waters when talking about the technical aspects of shooting, and I've fallen victim to it myself only to discover later that what I was told was the result of misinterpretation or just a mistake. I guess I get carried away trying to make sure that everyone in a discussion is on the same page.

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gelandangan
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PostPosted: Tue Jun 21, 2011 9:40 pm    Post subject: Re: Ballistic Stabilty Calculator Reply with quote

Mike,
IMO over stabilization also applies IF you are shooting for a particular purpose.

For example, as you may know over the years, that I like to shoot 30 cal projectiles at subsonic MV for hunting.
Usually for a 30 cal at subsonic, there is not enough energy to deform the projectile on impact.
As one of the main purpose of projectile deformation is to transfer energy by enlarging surface area of the impact site,
shooting at subsonic cannot tap into this.
Instead subsonics shooters are trying to just unbalance the projectile enough to TUMBLE on impact,
thus in a way creating the same effect as deformation, that is enlarging the impact surface area.

Here is where the stabilization applies.
If the projectile is spun at too high velocity, they would simply cruise through the flesh
and creating a very tiny (usually not even 30 cal) wound channel, thus not suitable for hunting.
The shooter with these particular need, would need to just stabilize the projectile to promote tumbling rather than punching.

Thus, as above, over stabilization applies for subsonics hunting.

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