Keeping a Sierra .308 168 HPMK Supersonic at 1 Mile?

[Bart B.]

4runnerman commented in an earlier thread about a .30-06:
It will push a 168 out to a mile supersonic. At 2630 FPS ,where i shoot my 175's it will stay supersonic out past a mile.Sierra Bullets says their 168 grain .308 HPMK needs about 4000 fps at the muzzle to do that.

Leaving at 2630 fps, Sierra also says their 30 caliber 168-gr. HPMK will go subsonic at about 1100 to 1200 yards. And their 175 grain .308 HPMK leaving at the same velocity will go subsonic at about 1300 yards.

Comments?

[4runnerman]

Be right back

[kraigwy]

You can play with the numbers all day. I have and tend to ignore them.

I've shot tons of 1000 yard matches over the years, and I know for a fact 168 SMKs do not work. They are erratic and they often key hole.

175/180 SMKs and the Mil Surplus 174s do.

I couldn't even get the 168s to work in my '06, let a lone my 308s.

Play the number/BD Calculator games all you want. To tell for sure, shoot at 1000 yards and see for your self.

Ballistic calculators and drop charts are guides, they may get you on paper but you need to shoot 'em to really see what happens.

[Slamfire]

I've shot tons of 1000 yard matches over the years, and I know for a fact 168 SMKs do not work. They are erratic and they often key hole.


Could not push them fast enough in a Garand. Darn 168's key holed. When you spend 2 hours getting to the match, one bad experience is all I needed to stop using 168's at 1000 yards.

175's worked well.

[Bart B.]

4runner, your chart shows both bullets going subsonic at about 1200 yards going about 1050 fps. 1050 fps is about what the speed of sound is.

The chart also shows both bullets moving at about 850 fps at 1760 yards, a mile down range. 850 fps is well below the speed of sound.

What do you think the speed of sound is?

Kraig and Slamfire, I've shot Sierra 168's in M852 ammo out of Garands leaving a bit over 2700 fps and 1000 yard accuracy was excellent. Same with a .308 Win. 26 inch barrel in a bolt gun pushing 'em out about 2750. But I do know that under 2600 fps, they usually go subsonic and start keyholing somewhere around 900 yards; this is why so many M14's and M1A's 22 inch barrels didn't shoot 'em fast enough. The two M14's I chrono'd some M852 ammo in shot 'em barely over 2500 fps. One guy with a new, tight, Obermeyer barrel on his M1A shot M852 fast enough to keep them supersonic at 1000 and shot excellent scores with it.

Shoot 'em fast enough and they'll do well at 1000.

[4runnerman]

That chart was a comparision between 168's and 175's. We are not allowed to shoot 168's in our matches as they say they have a tendency to tumble at 500 plus yards. I only shoot 175's . My Big Mistake. I had a false # on the sound of speed. Sorry to all for that. Oh Well Back to the drawing board again i guess.. Kraigwy- I e-mailed you on this one too. Looks like i should have listened a little bit (lots) better to what you wrote. Im a old German and as stubborn as a ox (my mom always said) ha ha. I still have not given up on the whole thing till i try it this summer.

[RKG]

For what it may be worth, the Sierra program shows a 168 SMK at MV = 2600 going sub-sonic at 940 yards. Same program shows the 175 SMK at MV = 2500 going sub-sonic at 1040 yards.

(Details:
OAT = 70F
MSL = 0'
Bar. = 29.53 in/hg.
V-sound = 1,132 fps.)

[kdog70]

What elevation? Not saying its possible but if you are shooting 10,000+ and given the right conditions and the bullet transitions well it may be possible to get hits not so much reliable hits but hits. If you could drive the bullet faster out of that 06 if you can it will help make a better argument. I have a shooting buddy that shoots an 3006 with 185 berger VLD somewhere just over the 2900 fps at 600' elevation and it peters out at 1400 ish yards but we can get hits to the mile steel but like i said its not reliable at all just throw lead out there and hope you hear a clang.

[5RWill]

Speed of sound is 1125fps give or take a couple of feet per second. 168s even at a proper speed still have a probability to become unstable due to the steep boattail IIRC. Even 175s are no where near supersonic out to a mile. kraig said it all actual data will trump theoretical data every time.

[Bart B.]

4runner man sez:We are not allowed to shoot 168's in our matches as they say they have a tendency to tumble at 500 plus yards. I'd ask those who mandate that to explain why 7.62 match ammo with Sierra 168's did very well at the Nationals' 600 yard line. Then ask them why commercial match ammo using the same bullet would shoot under 4 inches all day long at 600 yards in well rebuilt M1's, M14's and M1A's.

'Tis ok with me for folks to think that way. There's a bunch of myths floating around the shooting sports. There ain't enough paper on this planet to list 'em all in a book.

[5RWill]

168s are usually the standard for 600yd competitive matches like F-class from what information i gathered. And what my gunsmith has told me. If i'm not mistaken 168s hold some records for 600yd F-class correct?

[tobnpr]

.308 supersonic for a mile?
Maybe in the stratosphere...

[4runnerman]

Hello Blackops2-- F-Class is what my friend shoots. 168's are not allowed for 600 yard shoots. Now this is Minnesota so we are not big time here,but i would assume F-Class is F-Class. Most out there shoot 175's. Im new as of last year to bench shooting so all i can do is take the word of others that shoot out there.

[5RWill]

I see. Could be that different ranges vary a little. I'm not huge into F-class I'm more of a hitting steel at distance kinda guy. Or that's what I'm going for.

[Jim Watson]

When I first got into F class, there was a guy shooting 168 SMKs at 1000 (not in Minnesota) and doing quite well with them. His supply of bullets ran out, he bought more, and things went to pot. Apparently his old bullets were in some way different and better for the job.

Never heard of a 168 SMK being disallowed at 600 yards, or giving any trouble there. A higher BC bullet will still do better, they don't have to be unstable to be more subject to the wind than a 175 or other, but they don't fall apart until greater range. But the old name was the International, signifying optimization for 300 metres.

[Bart B.]

Speed of sound's...........
1156 fps at 96 degrees F.
1122 fps at 64 degrees F.
1087 fps at 32 degrees F.
1051 fps at 0 degrees F.

I edited this because I goofed on my first one. The above's what several on line calculators give. Thought speed would be higher at lower temperatures as the air's more dense. Wierd science.............

Sound travels faster in warm air because as the air gets colder, the molecules tend to get closer together, reducing their ability to have faster movements.

[the rifleer]

I suppose if you took a howitzer shell and necked it down to 30 caliber and used a 10 foot barrel you might have a chance...

[Art Eatman]

Elevation has an effect on the speed of sound. Thinner air = slower speed.

[4runnerman]

Ok OK OK...This thread could die anytime now..It started because some idiot (ME) did not have the facts when it came to the speed of sound,,Sorry to all. I was wrong and can admitt it. Thanks to all who have help me from time to time...:o

[Bart B.]

Art Eatman says elevation has an effect on the speed of sound. Thinner air = slower speed.

I disagree.

The speed of sound changes clearly with temperature, a little bit with humidity − but not with air pressure (atmospheric pressure). If sound speed did change with elevation, then music would sound off its original key if played at a different elevation it was recorded at.

[emcon5]

Art Eatman says elevation has an effect on the speed of sound. Thinner air = slower speed.

I disagree.

The speed of sound changes clearly with temperature, a little bit with humidity − but not with air pressure (atmospheric pressure). If sound speed did change with elevation, then music would sound off its original key if played at a different elevation it was recorded at.


NASA seems to think it does.

http://www.grc.nasa.gov/WWW/k-12/airplane/sound.html

Granted, it isn't much, according to their calculator:

1116 FPS @ sea level
1076 FPS @ 10K feet

That calculator doesn't have an input for temp, which has a much greater impact.

[bamaranger]

The first 1000 yd F-T/R match I ever went to (I've been to more 600 XTC types, but still a rookie irregardless), two of our bunch showed up with 168 factory match ammo, I think Black Hills, and had at it at 1000. Both guys left after the first relay. From their rifles, and barrel lengths, that ammo, supposedly grouped very well at 100, but by 1000 the slugs had "gone stupid" (wish I had thought of that phrase).

Just kind of pooped past at 1000.

I have never heard of "No 168's" at 600 for an F or F-T/R match either.

[Bart B.]

emcon5 comments about the speed of sound not changing with altitude:
NASA seems to think it does.
http://www.grc.nasa.gov/WWW/k-12/airplane/sound.html
Granted, it isn't much, according to their calculator

Here's a counter point:

http://www.sengpielaudio.com/calculator-speedsound.htm

[emcon5]

No offense to audio engineers, but I will defer to the rocket scientists on this one.

In reality, whether it does or not isn't all that relevant, as it is only a 40 FPS difference (according to NASA), and the effect of altitude/air density on drag plays a much bigger role in LR target shooting than the speed of sound.

For example, my 6.5-06 shooting 140 SMKs at ~2900 fps, on a 59ºF day according to JBM (http://www.jbmballistics.com):

At sea level, is still traveling 1406 FPS at 1000 yards., and goes subsonic at around 1350 yards.
At 5000ft elevation, the bullet is traveling 1605 FPS at 1000 yards, and goes subsonic at around 1600 yards.

In the same conditions, a .308 168MK @ 2700 FPS:

At sea level is traveling 1105FPS at 1000 yards, and is subsonic*.
At 5000 Ft, is traveling 1273 FPS at 1000 Yards and does not go subsonic until 1200 yards.

*According to JBM, and the sound engineer calculator linked above agrees, the speed of sound at 59ºF is 1116.4 FPS. It is also interesting to note, that JBM does not adjust the speed of sound with altitude.

[Bart B.]

Blackops mentions: 168s are usually the standard for 600yd competitive matches like F-class from what information i gathered.When the .308 Win. was "the" cartridge used in NRA high power rifle competition, the favorite bullet for best accuracy and scores was the Sierra 190 HPMK in both bolt guns and 7.62 Garands. Sometimes, Sierra's 200 HPMK was used in bolt guns. I watched Corky Tyson put twenty 200's into about 4 inches at 600 yards using aperture sights setting the record for that prone course of fire. David Tubb shot Sierra's 250 HPMK's in a 1:8 twist barrel leaving at 2150 fps and shot very accurate indeed.

[mapsjanhere]

300 RUM, 210 Berger VLD, 5000 ft altitude, problem solved ;). Now if I could only find a 1 mile range to try it out.

[5RWill]

I honestly want a 30-338 lapua. I know brass would be outrageously expensive. But i would love to be throwing 240gr SMKs out of it. I guess by that weight in .30 cal you might as well just go .338. I want to try some 220 smks or 240 smks in my .300 wby though.

[Hardcase]

The reason that calculators (and tables) show a change in the speed of sound with altitude is that a certain decrease in temperature as altitude increases is assumed.

The reason that altitude doesn't affect the speed of sound is because the density and pressure offset each other. The air pressure goes down, but the density goes up. And that's because as one ascends in a column of air, as the temperature decreases, the density increases, while the amount of air in the column decreases, lowering the pressure. This holds true up through the stratosphere, at which point ozone heating comes into play and the speed of sound goes up...and eventually, the air goes away.

There are some meteorological exceptions to the rule, such as with high altitude winds or around thunderstorms, where the air does not behave uniformly, but who's out shooting in a thunderstorm?

By the way, we should be happy that air behaves the way that it does. In other mediums (like water, for instance), different frequencies have different speeds of sound.

As far as keeping a bullet supersonic at a mile, I have no idea...I can barely see the target at 200 yards.