New Sierra 6.5 MK

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cslcAl
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Re: New Sierra 6.5 MK

Post by cslcAl »

Jason

I ran the numbers on my ballistics program 1549 ft/lbs of energy at 500 meters.
I’ve never shot any bullet with that kind of energy at 500.
We’ll see but I’ll be surprised if I ring any.

When you hold one of these bullets in your hand they look just down right nasty.

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Re: New Sierra 6.5 MK

Post by Another Dang 9 »

Al, has Sierra posted new load data for the new "nasty"?
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Re: New Sierra 6.5 MK

Post by cslcAl »

Here’s what they posted for a 6.5 Creedmoor.

https://sierrabulletsblog.com/2017/01/0 ... load-data/
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Re: New Sierra 6.5 MK

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I got to shoot a HP match this month here in AZ at Ben Avery. We came over the day before and got to practice also. I’m happy to report that the new 150 MK’s take the rams down with authority. I’d highly recommended them. My gun has a 1-7 twist barrel, but I know shooters who are using them with a 1-8 twist with good results also.

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Re: New Sierra 6.5 MK

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cslcAl wrote: Tue Feb 26, 2019 1:21 pm I got to shoot a HP match this month here in AZ at Ben Avery. We came over the day before and got to practice also. I’m happy to report that the new 150 MK’s take the rams down with authority. I’d highly recommended them. My gun has a 1-7 twist barrel, but I know shooters who are using them with a 1-8 twist with good results also.

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Thanks again for the updates on those bullets, Al. Do you have a guess at how fast the shooters with 1:8 twist barrels are pushing the 150s to get them to stabilize well?

I am shooting a 260 Rem, so should have plenty of case capacity. Once I run through these 143 ELD-X bullets, I'm planning to give those 150 MKs a try. My complication with that is that I can't really test out past 200 meters other than at the few high power silhouette matches I get travel to shoot each year. My local range is only 200 meters long for the usual member shooting. I'm worried that I'll get them to stabilize fine out to 200 meters but then groups will fall apart somewhere between there and 500 meters.
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Re: New Sierra 6.5 MK

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Jason, I contacted one of the 1-8 twist users. He is getting 2700fps with a 6.5x 47. Works well for him.

I would think if your rifle groups at 200 you’d have no trouble at 500.

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Re: New Sierra 6.5 MK

Post by Varn »

Jason. There should be an online stability calculator somewhere. You bring up an excellent point of discussion
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Re: New Sierra 6.5 MK

Post by jeff59 »

Here's a link to the JBM stability calculator.
https://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

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Re: New Sierra 6.5 MK

Post by cslcAl »

I use the Ballistics App and it has a built in stability calculator that uses the Miller formula.

Using my load data my 1-7 twist has a stability of 1.85
Substituting a 1-8 comes out to 1.41.

So Jason, Does this help.

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Re: New Sierra 6.5 MK

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cslcAl wrote: Thu Feb 28, 2019 8:54 am I use the Ballistics App and it has a built in stability calculator that uses the Miller formula.

Using my load data my 1-7 twist has a stability of 1.85
Substituting a 1-8 comes out to 1.41.

So Jason, Does this help.

Al Foust
Thanks, Al. It does help a bit. The standard formula and recommendation that stability be between 1.3 and 2.0 makes me think a 1:8 twist barrel will be marginal for stability.

At 2700 fps from a 1:8 twist barrel, that bullet (1.5" length) should have stability factor of 1.391, which is well within the recommended range. That means that it will be plenty stable initially with a 2700 fps muzzle velocity. Once it drops below 2200 fps, which should happen somewhere around turkey distance, the stability factor drops below 1.300. Out near rams at 500 meters, the velocity will be around 2050 fps which means the bullet will have a stability factor of 1.269. Of course, by the time it's at the ram the stability factor means less.

The fact that stability factor dropped below 1.300 at the turkeys and still has a long way to go to rams is what worries me. That's why I was hoping for results from shooters actually shooting those bullets from 1:8 twist barrels. The calculations with quoted BC from Sierra aren't really conclusive unless muzzle velocity is at least 2875 or so.

I'm a bit unclear on one detail of the stability factor calculation, though. Is the recommendation that the factor be at least 1.300 at the muzzle to provide a stable flight for any reasonable distance, or is the recommendation that the stability factor be at least 1.300 for the entire flight to the target?
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Re: New Sierra 6.5 MK

Post by jbzeus »

Wanting to try out HP. I'm still waiting to see what the verdict is on these 150 SMK. Any feedback? I haven't seen any updates on the sited I visit.
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Re: New Sierra 6.5 MK

Post by mychippy »

Jason wrote: Thu Feb 28, 2019 12:04 pm
cslcAl wrote: Thu Feb 28, 2019 8:54 am I use the Ballistics App and it has a built in stability calculator that uses the Miller formula.

Using my load data my 1-7 twist has a stability of 1.85
Substituting a 1-8 comes out to 1.41.

So Jason, Does this help.

Al Foust
Thanks, Al. It does help a bit. The standard formula and recommendation that stability be between 1.3 and 2.0 makes me think a 1:8 twist barrel will be marginal for stability.

At 2700 fps from a 1:8 twist barrel, that bullet (1.5" length) should have stability factor of 1.391, which is well within the recommended range. That means that it will be plenty stable initially with a 2700 fps muzzle velocity. Once it drops below 2200 fps, which should happen somewhere around turkey distance, the stability factor drops below 1.300. Out near rams at 500 meters, the velocity will be around 2050 fps which means the bullet will have a stability factor of 1.269. Of course, by the time it's at the ram the stability factor means less.

The fact that stability factor dropped below 1.300 at the turkeys and still has a long way to go to rams is what worries me. That's why I was hoping for results from shooters actually shooting those bullets from 1:8 twist barrels. The calculations with quoted BC from Sierra aren't really conclusive unless muzzle velocity is at least 2875 or so.

I'm a bit unclear on one detail of the stability factor calculation, though. Is the recommendation that the factor be at least 1.300 at the muzzle to provide a stable flight for any reasonable distance, or is the recommendation that the stability factor be at least 1.300 for the entire flight to the target?
This topic has been covered in great detail over at accurateshooter.com. If I recall, the stability factor is considered at the muzzle. If your stability factor is on the low side (between 1 and 1.5?), you may lose a few points off your ballistic coefficient from the bullet wiggling around. That situation will be constant until your supersonic crossing, at which point the bullet could tumble, or not. For silhouette, I wouldn't think losing a little off a super high BC would matter much.
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