Optimum muzzle velocity for subs?

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BlakeJ
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Optimum muzzle velocity for subs?

Post by BlakeJ »

When loading your own subs, what muzzle velocity should you shoot for to keep it subsonic?

You read a lot about how 1050 fps is the best, but can you push it a little faster depending on elevation and outside temperature?

Knowing that the speed of sound is 1125 fps at sea level, how close can you push it?
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CanOfWhooppass
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Re: Optimum muzzle velocity for subs?

Post by CanOfWhooppass »

What is the goal?
My understanding is slower is quieter with all else being equal.
If it's terminal performance it mostly matters that you start with a good bullet design and stay within its designed velocity range.
If it's knocking down plates it is more bullet weight.
If it's distance then balistic coefficient matters most.

I doubt an extra 50 fps would change anything in a meaningful way.
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Re: Optimum muzzle velocity for subs?

Post by BlakeJ »

The goal is to get as fast as possible without getting a supersonic crack. This will be on a big bore setup, so I'm wanting to move the giant bullets as fast as I can without getting the supersonic crack, so I'll still stay super quiet through the can.
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Re: Optimum muzzle velocity for subs?

Post by glocker17 »

Mine run about 1020 and don't go trans sonic regardless of conditions.
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Re: Optimum muzzle velocity for subs?

Post by Fulmen »

There is no real optimum speed, slower will always be more quiet:
Image

The reason for this is that air flow around the bullet will be higher than it's actual velocity, so even if you stay below the speed of sound the flow around the bullet may exceed it. This is the trans-sonic range. As you can see the noise really increases more rapidly at around 300-320m/s, so most people choose this range.
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L1A1Rocker
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Re: Optimum muzzle velocity for subs?

Post by L1A1Rocker »

The bullet is also rather unstable in the trans-sonic stage. Accuracy is not so good. The 1050 goal is a bit dated. Most now shoot for 1010.
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Re: Optimum muzzle velocity for subs?

Post by Joshua@CapitolArmory »

I may be the exception to what most guys do, but I don't load for speed with subs. I get a general range of, then work up based on accuracy. I'll usually start to see the groups open up before it gets into trans/super territory... so if I push 990-1010 and accuracy is great then I'm happy with it.

It's a sub, so I would rather take that then trying to squeeze out the maximum velocity. Of course you can go overboard trying to get the exact velocity you want and peak accuracy there, but that's too much work for me. I just want some accuracy and quiet 208 AMAX loads to ring steel with.
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Gyrkin
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Re: Optimum muzzle velocity for subs?

Post by Gyrkin »

BlakeJ wrote:Knowing that the speed of sound is 1125 fps at sea level, how close can you push it?
Elevation has very little effect on the speed of sound. Humidity had a little, but the biggest factor is temperature. At 100 degrees the speed of sound is 1160 fps and at 0 degrees it's 1050 fps.
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Re: Optimum muzzle velocity for subs?

Post by T-Rex »

Joshua@CapitolArmory wrote: so if I push 990-1010 and accuracy is great then I'm happy with it.
Agreed
I aim for 950, with initial loading, and try to bracket around this velocity to get my accuracy node.
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Re: Optimum muzzle velocity for subs?

Post by whiterussian1974 »

Gyrkin wrote:
BlakeJ wrote:Knowing that the speed of sound is 1125 fps at sea level, how close can you push it?
Elevation has very little effect on the speed of sound. Humidity had a little, but the biggest factor is temperature. At 100 degrees the speed of sound is 1160 fps and at 0 degrees it's 1050 fps.
You're right. Unless someone plans a hunt from K2 or during descent from a plane @ 10k', altitude doesn't matter much for 99.8% of people living below Silverton or Blue River, CO.

If planning a hunt in Peruvian Andes, I would develop my load locally. Otherwise, Joshua's post about accuracy is the best advice. It is a great indicator of transonic turbulence.
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BlakeJ
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Re: Optimum muzzle velocity for subs?

Post by BlakeJ »

Does bullet size help any with trans sonic accuracy? I would think the bigger the bullet the less it would effect it, but I could be wrong.
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Re: Optimum muzzle velocity for subs?

Post by rimshaker »

Sub is sub. Optimum to me means remaining subsonic across a wide temp range. Whether you're shooting in MN during winter, or in FL during summer.
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Re: Optimum muzzle velocity for subs?

Post by Capt. Link. »

The range of 900-950 fps is used by pro's including our military.Target grade ammo is in the same range.
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Re: Optimum muzzle velocity for subs?

Post by Gyrkin »

Capt. Link. wrote:The range of 900-950 fps is used by pro's including our military.Target grade ammo is in the same range.
That would keep is subsonic all the way down to -85 F. Cold even by Wyoming standards.
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Re: Optimum muzzle velocity for subs?

Post by BlakeJ »

I'll do some tinkering. It's about a 20% energy difference per 100 fps.
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Re: Optimum muzzle velocity for subs?

Post by TheSpaniard »

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Re: Optimum muzzle velocity for subs?

Post by whiterussian1974 »

985'/s w/ 80 Extreme Spread and 35 Standard Deviation should be fine. These are more reasonable figures for most loaders.

40/10 is pretty tight unless you've got a large powder capacity and 103-108 load density. (Slightly compressed)
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Capt. Link.
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Re: Optimum muzzle velocity for subs?

Post by Capt. Link. »

Gyrkin wrote:
Capt. Link. wrote:The range of 900-950 fps is used by pro's including our military.Target grade ammo is in the same range.
That would keep is subsonic all the way down to -85 F. Cold even by Wyoming standards.
That speed range accounts for all the variables plus loss of life if a bullet goes transonic.
Accurate shot placement and deep penetration counts.
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Re: Optimum muzzle velocity for subs?

Post by Mageever »

whiterussian1974 wrote:
Gyrkin wrote:
BlakeJ wrote:Knowing that the speed of sound is 1125 fps at sea level, how close can you push it?
Elevation has very little effect on the speed of sound. Humidity had a little, but the biggest factor is temperature. At 100 degrees the speed of sound is 1160 fps and at 0 degrees it's 1050 fps.
You're right. Unless someone plans a hunt from K2 or during descent from a plane @ 10k', altitude doesn't matter much for 99.8% of people living below Silverton or Blue River, CO.

If planning a hunt in Peruvian Andes, I would develop my load locally. Otherwise, Joshua's post about accuracy is the best advice. It is a great indicator of transonic turbulence.
Yep. I have some subsonic ammo that was going super on me a while back when it normally never would. I was at 10,000 ft. altitude. I live close to 5000 ft., and usually temp will swing it a bit as I head up the canyons, but you add the temp altitude and it's definitely a factor some of us deal with.

I'm all for the advice from Josh to start low and work up based on accuracy.
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Re: Optimum muzzle velocity for subs?

Post by Gyrkin »

Mageever wrote:Yep. I have some subsonic ammo that was going super on me a while back when it normally never would. I was at 10,000 ft. altitude.
I don't think 10,000 feet would be high enough to make a noticeable difference. Plus, if I'm not mistaken the high altitude would increase the speed of sound, because of the thinner air, and therefore make it easier to keep under it. But even then altitude has very little effect on speed of sound, temperature has a big effect. If it was colder up there at 10,000 feet, that was the reason, not the altitude.
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Re: Optimum muzzle velocity for subs?

Post by whiterussian1974 »

You're both correct. The drop in Temp is coupled to the rise in Alt. (Lapse Rate)

http://www.onthesnow.com/news/a/15157/a ... mperature-"Thus meaning it's a change of 6 degrees Celsius per 1,0000 meters.) ... change * 3.3F per 1,000ft, or 3 * 3.3 = about 10F temperature decrease)"

https://en.wikipedia.org/wiki/Lapse_rate
"under normal atmospheric conditions the average atmospheric lapse rate results in a temperature decrease of 6.4 °C/km (3.5 °F or 1.95 °C/1,000 ft)"
"(3.56 °F or 1.98 K/1,000 ft from sea level to 11 km (36,090 ft or 6.8 mi)) . From 11 km up to 20 km (65,620 ft or 12.4 mi), the constant temperature is −56.5 °C (−69.7 °F)"
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Re: Optimum muzzle velocity for subs?

Post by bani »

L1A1Rocker wrote:The bullet is also rather unstable in the trans-sonic stage. Accuracy is not so good. The 1050 goal is a bit dated. Most now shoot for 1010.
this is dependent on bullet design. there are bullets which are specifically designed to be 100% stable through transonic range.
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Re: Optimum muzzle velocity for subs?

Post by L1A1Rocker »

bani wrote:
L1A1Rocker wrote:The bullet is also rather unstable in the trans-sonic stage. Accuracy is not so good. The 1050 goal is a bit dated. Most now shoot for 1010.
this is dependent on bullet design. there are bullets which are specifically designed to be 100% stable through transonic range.
Cool, which ones are those? I'd love to get some.
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Re: Optimum muzzle velocity for subs?

Post by bani »

L1A1Rocker wrote:
bani wrote:
L1A1Rocker wrote:The bullet is also rather unstable in the trans-sonic stage. Accuracy is not so good. The 1050 goal is a bit dated. Most now shoot for 1010.
this is dependent on bullet design. there are bullets which are specifically designed to be 100% stable through transonic range.
Cool, which ones are those? I'd love to get some.
bryan litz created bullets for berger that are explicitly designed to be transonic stable.

http://www.longrangehunting.com/forums/ ... post494399
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Re: Optimum muzzle velocity for subs?

Post by L1A1Rocker »

bani wrote:
Cool, which ones are those? I'd love to get some.
bryan litz created bullets for berger that are explicitly designed to be transonic stable.

http://www.longrangehunting.com/forums/ ... post494399[/quote]

Tried to check it out following the link at the link you posted and got this:
Dangerous Website Blocked

You attempted to access:

http://appliedballisticsllc.com/TacticalAmmo.html

This is a known dangerous website. It is recommended that you do NOT visit this site. The detailed report explains the security risks on this site.

For your protection, this web page has been blocked. Visit Symantec to learn more about phishing and internet security.
Just to be clear, a bullet that is being claimed to trans-sonic stable sounds like snake oil to me. And that dangerous site seems to point that direction also.

Do you or anyone you can link to have any first hand experience with these bullets?
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