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When does my 168 go subsonic?

This is a discussion on When does my 168 go subsonic? within the Bolt Action forums, part of the Gun Forum category; Here's my direct experiences with REAL world conditions and the 168 SMK at 750+ yds. I took the Sig Saur "reach for a thousand" instructional ...


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Old October 31st, 2016, 11:26 AM   #46
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Here's my direct experiences with REAL world conditions and the 168 SMK at 750+ yds. I took the Sig Saur "reach for a thousand" instructional clinic and I chose to use my 300WM over my 308. I was skeptical that I could consistently reach 1K with my 1-12 twist R700 Varmint. There were 3 students using rented Sig SSG 3000 rifles but the class ran out of the FGMM 175 gr ammo and the shooters had to use FGMM 168 gr ammo. All the shooters did well up to 750 yds, however the last leg of the training was 1000 yds and that's where the inconsistent hits started to happen. Our instructor even commented that they've had transonic issues trying to take the 168's to 1K. Meanwhile my 300WM 208 Amax's at 2740 fps shot OUTSTANDING ! Out of a class of 8 students I had to settle for second place as I got beat by an excellent fellow shooter using a 6.5 Creed.

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Old October 31st, 2016, 01:04 PM   #47
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... So when does it slow down enough to wobble again? This thread was never about which program was best.
I've already explained it. Depends on velocity, atmospherics, altitude, etc. I simply plugged some numbers into a ballistic program, and looks at where the bullets should start to go transonic. The more dense the air, the faster the bullet slows down.

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Old November 6th, 2016, 03:42 PM   #48
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Do you have proof that the ELD bullets tips still melt? If not, your "falsehood" statement is strictly opinion. And of course Hornady advertises that their bullets are better than everyone else's, so does every other manufacturer. Hornady, Berger, Barnes, etc. choose to keep improving on their designs, whereas Sierra seems to rest on their past, and keep increasing their prices. The TMK was a response to the market wanting them to produce a polymer tipped bullet, and to try to compete with Hornady, and Nosler.
Don't twist my words. I said nothing about Hornady's polmer tips melting. I don't believe they do, nor does anyone elses. In fact I believe this whole issue was a manufactured problem that Hornady 'created' a solution for.

Yes, every bullet maker thinks their are the best, only Hornady goes out of their way to bash everyone else. I've dealt with their reps at Perry before, mention to them that a rifle shoots another maker's bullet better than theirs and you'd think you slapped their grandma on the butt in front of them.

Seems to me that Sierra is in an enviable position that they don't have to chase all the other bullet maker's trends to keep up. I don't see any Hornady bullets being used in too many commercial ammo manufature and despite Federal's ability to make all kinds of bullets in house they're still buying a LOT of bullets from Sierra as well as having many custom made for them, so despite your claims they must be doing something right.

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Old November 6th, 2016, 03:44 PM   #49
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... So when does it slow down enough to wobble again? This thread was never about which program was best.
Depending on a myriad of variables, somewhere between 700-900 yards.

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Old November 6th, 2016, 04:00 PM   #50
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You can pretty well count on subsonic at about 850 yds, ie round holes at 800 and problems at 900. If u are on a range that has buts to pull targets at 1000, it can be dangerous to the men pulling your target.

As stated use 175 gr or if a bolt gun 190 SMK works well except u may run out of elevation before 1000 yds with the 190's..

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Old November 6th, 2016, 05:29 PM   #51
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Depending on a myriad of variables, somewhere between 700-900 yards.
So shooting an M1A gas gun 600/800?

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Old November 6th, 2016, 07:32 PM   #52
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761.2 mph, 661.5 knots, or 1116 ft/s?
Depends on temperature.

A 30 dergree increase in temperature will increase the speed of sound about 75 fps.

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Old November 6th, 2016, 07:34 PM   #53
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So shooting an M1A gas gun 600/800?
Just shoot better bullets (175 gr) . . . .

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Old November 6th, 2016, 07:40 PM   #54
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Depends on temperature.

A 30 dergree increase in temperature will increase the speed of sound about 75 fps.

??? so a dumb question from a 'learner' here: So hotter means farther?

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Old November 7th, 2016, 06:41 AM   #55
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??? so a dumb question from a 'learner' here: So hotter means farther?
No, shorter. The higher the speed of sound the sooner the bullet decelerates to sub-sonic velocities, the shorter the distance travelled.

If the speed of sound is 1120 fps (60 F) and the muzzle velocity is 2600 fps the launch Mach number is M 2.32. If the speed of sound is 1160 fps (95 F), the launch Mach is M 2.24.

The velocity at to 800 yards is, say for example 1250 fps, at 95 F, the bullet is at M 1.08, well inside the transonic region, at 60 F, it is at M 1.12 just entering the transonic region.

At 20 degrees F, the speed of sound is 1070 fps, if we use the same info above at 800 yards, the bullet is at Mach 1.17, still well supersonic.

(Also, it seems I overstated how much the speed of sound increases with a 30 degree temperature increase...it's only 40 - 45 fps.)

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Last edited by lysander; November 7th, 2016 at 07:31 AM. Reason: Fundamental error.
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Old November 7th, 2016, 07:00 AM   #56
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Any experience based opinions on JBM ballistics calculator?
I ask because it's been within two 1/4"/100 yard clicks at 600 yards for me

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Old November 7th, 2016, 07:42 AM   #57
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-stuff-
Also, if you start at a lower Mach number your initial drag is higher, so the slow down faster.

Below is a drag function of drag coefficient against Mach number. You want to keep the Mach number high, so the drag coefficient is low.



This is the reason sea level speed records for aircraft are done in Death Valley in the summer. The higher the temperatures, the higher the actual MPH or knots for any given Mach number.

Also, aircraft are limited in the dynamic pressure (q) they can withstand. Density is a factor in calculating q, so the lower density of hot air helps keep q lower.

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