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Old August 27, 2012, 11:03 AM   #1
Clark
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120 gr bullets stabilize in a 10" twist 260 Rem?

I would rather use the 120 gr Nostler ballistic tip bullets [1.220" long].
I would like to shoot animals out to 500 or 600 yards, and want the bullet to remain stable down to ~ 2000 fps.
This calculator make it look like I am ok.
http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi
This calculator makes it look like I am only good down to 2500 fps
http://kwk.us/twist.html
And that SG variable.... How would I measure the density of bullets? Drop them in water and weigh the spillage?
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Old August 27, 2012, 12:17 PM   #2
Jimro
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Do you have a scientifically graduated cylinder?

Drop them in water and measure the displacement. You know the mass of the bullet, and the volume of displacement in water will give you a cubic centimeter measurement.

Density = Mass/Volume

If you don't have one fine enough, just use more bullets to get a bigger difference and then divide your final number by that number.

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Old August 27, 2012, 06:06 PM   #3
Clark
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Quote:
Jimro
Do you have a scientifically graduated cylinder?
I had one for mixing drinks, but I quit drinking in 1982.
I am shocked... SHOCKED, I tell you, over the cavernous lack of information on this subject. I wrote Nosler this morning. So they tried the first link I posted, and then concluded it must be good.
I can imagine a market niche, "Bullet Review Magazine".
I could afford to run it per the C.K. Lewis pet store biz model.
Seriously folks, doesn't it seem odd that they sell us barrels and bullets and we don't know what happens when we put them together?
100,000,000 gun forum posts into this century and we don't have elementary empirical data?
I feel like a fool. I buy lots of barrels and bullets and it is anyone's guess what will happen when I put them together.
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Old August 27, 2012, 06:26 PM   #4
Jimro
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I honestly don't know how that bullet will perform in that barrel at those velocities. The one guy who ever got good results at 1K with 168gr BTHP's in a 308 Win was using a 1:13 twist in his barrel, which goes against the common wisdom about twist rates and transonic bullet transitions.

With a 1:10 you are looking at 11% slower rpms on the bullet than the standard 1:9 twist that everyone says is good to go for up to 130gr bullets. 8% lower mass, 11% lower rpm, your initial velocity is going to be pretty high from the 260 Rem case, I think you are in no danger of going subsonic out to 600.

I'd say go for it, as if the 120s don't work out there are some good choices in the 90 to 115gr range that you could fall back on that are sure to be stabilized with a 1:10 twist.

Sorry I couldn't be more help.

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Old August 27, 2012, 08:13 PM   #5
603Country
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I don't outright know the answer to your question. But...I shoot that bullet in my 260, which is a Ruger 77 Compact with a 16.5 inch barrel. What I don't know is the twist rate in that rifle. I guess I could go check or maybe Google it up.

As for range, I've only used it on critters to about 400, so that still doesn't answer your question.
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Old August 28, 2012, 09:01 AM   #6
GeauxTide
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Twist on the Ruger Compact is 1-8". I'm surprised to hear of a 260 with a 10" twist. I'd look at the 100gr Nosler.
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Old August 28, 2012, 08:29 PM   #7
hodaka
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I have an older Remington VLS .260. It has been a while since I measured it but I think it is a 10 twist. It shoots 120 Sierra SMK's and Hornady AMax's very well but scatters all of the 140's I have ever tried. It does not like the 100's or 85"s very well either. The 120's will shoot under an inch at 200. Have only shot paper with it.
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Old August 29, 2012, 07:42 AM   #8
Doyle
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Hodaka, that's the first 1 in 10 twist .260 I've hever heard of from Remington. The rest I've seen have 1 in 9.
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Old August 29, 2012, 08:10 AM   #9
Bart B.
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Jimro sez:
Quote:
The one guy who ever got good results at 1K with 168gr BTHP's in a 308 Win was using a 1:13 twist in his barrel, which goes against the common wisdom about twist rates and transonic bullet transitions.
I've got sub MOA at 1000 with Sierra 168 HPMK's from a 1:13 twist. They left at about 2770 fps from the 32 inch barrel with 44.5 grains of IMR4064.

It's not the the rifling twist alone that stabilized bullets in flight for long ranges. It's the rpm's they start with. Slower twists and high velocity spins a given bullet the same rate as a fast twist and low velocity. That 168 needs to be spun at least 150,000 rpm out the muzzle to stabilize it to 1000 yards. And leave at least 2700 fps to remain supersonic through 1000.

2600 fps, 1:12 twist = 156,000 rpm (M852 match ammo from M14, M1A; subsonic at 1000)

2770 fps, 1:13 twist = 153,415 rpm (supersonic at 1000)

Note that Sierra 168 International Match BTHP (later renamed a Match King) bullet was first made for free rifles used in 300 metre international competition. They were shot with reduced loads giving about 2500 fps out of the 1:12 twist 26 inch barrels used. Excellent gold medal winning accuracy was attained in the Olympics.

Last edited by Bart B.; August 29, 2012 at 09:06 AM.
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Old August 29, 2012, 01:55 PM   #10
Clark
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Bart,
I did not think of that. The R.P.M.'s do not slow down at the same rate that the bullet velocity slows down.

So if hodaka's rifle is good at any range, mine is probably good at long range.

Now I feel dum
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Old August 29, 2012, 04:10 PM   #11
hodaka
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Doyle, I'll try to check it again this weekend when I'm back home. I didn't know the twist when I bought it but when I measured it I'm almost sure it was 1 in 10. In any case it won't shoot a 140, Berger, Hornady or Sierra.
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Old August 31, 2012, 12:55 PM   #12
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Doyle, you are correct. It is a 1 in 9.
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Old August 31, 2012, 03:33 PM   #13
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Hodaka, my Rem Model 7 with the 1 in 9 twist shoots the Federal Premium 140gr Sierra Gamekings just fine. You might want to give those a try for a factory ammo. I've got a batch of reloads my buddy worked up using 128grn Hornady SP Interlocks. Those look they are going to be just the right combination of length and weight.
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