January 29, 2015, 12:07 AM | #1 |
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Hornady 178 gr match hpbt
I'm interested in hearing some of your guys loads for this particular bullet in .308. In my atmosphere, about 4,000 feet, my ballistics calculator shows my load will stay super sonic to 1600 yards, Id say outstanding for a .308. I'm loading the 178 grain bullet in lake city match brass with 42.5 grains of imr4895. The overall length is 2.835 with a velocity of 2700 fps. What are you guys loading and getting for velocity? Anybody have experience with this bullet going transonic and if so did it handle it well or did it tumble? Hope to hear from you guys. Thanks.
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January 29, 2015, 06:32 AM | #2 |
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I'm sitting around 200ft elevation, and I'm running around 2650fps. I use IMR 4064 and 2000-MR. Depending on brass I use, I can get a little more velocity.
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January 29, 2015, 10:28 AM | #3 |
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Sierra's software says it'll start dropping into the sub sonic range at about 1200 yards.
IMR4064's proved a much better powder for accuracy in the .308 with bullets heavier than 165 grains up to 190 grains than IMR4895, but you've got to weigh the charges; metering them doesn't work. I've shot 43 grains of it under Sierra's 180 HPMK with sub MOA through 1000 yards. |
January 29, 2015, 11:45 AM | #4 |
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I'm loading 45 grains of Varget, CCI BR-2 primers, and Lapua cases, COAL is 2.770". Out of my 20" barrel I'm averaging 2640 fps at sea level. With the rifle zeroed at 100 yards the average drop at 300 is 13.5".
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January 29, 2015, 01:49 PM | #5 |
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If I set up QuickTARGET Unlimited to believe Hornady's claimed G1 BC for this bullet of 0.53, and set the atmospheric conditions to ICAO standard, which is 45°F at 4000 feet at which the speed of sound is 1101 ft/s, and with a barometric pressure of 25.84 in-Hg, I get subsonic at about 1410 yards.
However, Hornady's G1 BC's tend to apply only near muzzle velocity, as Bryan Litz's measurements show, and to get lower as speed drops off. And if I convert the G1 BC of 0.53 to its G7 BC of 0.261 at that velocity, knowing the G7 drag function tracks the low drag bullet's actual drag curve more closely than the standard G1 drag model does, and I adjust the temperature to a more comfortable 70°F, where the speed of sound rises to 1128 fps, and leave the barometric pressure alone, the bullet goes subsonic at about 1285 ft/s. So the subsonic range depends greatly on the details. Using Hodgdon's test barrel data for 175 and 180 grain bullets, it looks like 42.5 grains of powder would get you 2552 fps in a 24" minimum chamber test barrel. You'd need something closer to a 30" barrel to get to 2700 fps with 42.5 grains of IMR 4895, even with the tighter LC case. I don't know what barrel the OP has, but if it's not a long tube and he's reading 2700 fps on a chronograph, I would consider the readings suspect and try moving the instrument back a little and setting it on a dark tarp if the area has light colored ground, to avoid ground light glinting off the bullet.
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January 29, 2015, 05:53 PM | #6 |
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Lake City arsenal got 2550 fps average at 26 yards from the muzzle with M119 7.62 NATO match ammo's 172-gr. bullet. Actual muzzle velocity was close to 2600 fps. at max pressures of 50K cup. Their test loads started with 42 grains of IMR4895, then adjusted +/- a few tenths to get velocity at 78 feet of 2550 fps +/- 30 fps so sight settings for range zeros through 1000 yards on service rifles would be virtually the same across all lots of ammo.
Why arsenals picked 26 yards for chronograph reference distance checking rifle and machine gun ammo velocities is explained by Hatcher in his book: https://books.google.ca/books?id=yES...20ammo&f=false I used to think muzzle velocity was about 50 fps faster at the muzzle but that article seems to say they add about 50 fps to what the chronograph gets at 78 feet for what the ammo has. |
January 30, 2015, 06:29 PM | #7 |
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Interesting replies guys thank you very much! I do wonder about the velocity reading due to the fact that I haven't ever tested it against someone else's chrono and I did buy it used. However, my ballistic calculator, called "ballistic" from the Apple Store on my iPhone, gives me very accurate drop data for the bullet with its BC at .53 and a velocity of 2700 fps 10 feet from the muzzle. I'm getting first shot hits out to a thousand yards. This leads me to believe that the data must be working for me. The rifle is a savage model 10 FCP-K with 24 inch barrel. My main question is if anyone has experience with stretching this bullet to its absolute limits, past transonic. Will it tumble? Or will it maintain its flight. And if not are there any bullets out there capable of going transonic and maintaining stability?
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January 30, 2015, 08:21 PM | #8 |
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Long, slender spitzer boattail bullets change direction more so than short blunt nose ones as they go transonic. 45 caliber 500 grain flat based round nose bullets shot very accurate in 1000 yard matches in the late 19th century after going subsonic before hitting targets. Their 800, 900 and 1000 yard target was used for 30 caliber long range matches until 1973 when its scoring rings were made smaller.
A .300 Win Mag will keep heavy bullets supersonic to 1500 yards. Last edited by Bart B.; January 30, 2015 at 08:29 PM. |
February 1, 2015, 09:25 AM | #9 | |
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Quote:
I have found that the Ballistic AE app does very well for me as well with my 178's. I have also found, by playing with the G1 and G7 settings, that when I have it set with G1, my results are more accurate. I don't care what anyone says, this is what I've seen testing it. |
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February 1, 2015, 07:29 PM | #10 | ||
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Quote:
Bryan Litz says the 168 grain SMK has a dynamic instability problem in the transonic region. I've seen it tumble still going about 1350-1400 fps. Dynamic instability overshoots corrections. In this bullet it seems to happen mainly in a side wind, that I've observed, and may not happen in still air with some rifling twist rates. Quote:
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.308 reloads , 178 gr , hornady , imr4895 , transonic |
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