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Posted: 12/5/2018 5:33:37 PM EDT
Does anyone know of a source to get G7 BC's for Sierra bullets, they only list G1's on their website?
Bullet 142 gr. HPBT TMK Dia. (inches) .264 Weight (grains) 142 Sectional Density .291 Ballistic Coefficients and Velocity Ranges .626 @ 2850 fps and above .611 between 2400 and 2850 fps .606 between 2050 and 2400 fps .581 @ 2050 and below |
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Posted: 12/5/2018 5:48:33 PM EDT
[Last Edit: AKSnowRider]
[#1]
Ab list it as .295 G7 in my kilo 2400 library..It only list it as the 142 grain Match King though.. For the pointed 142 grain Match king it list as .311 G7...
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Posted: 12/5/2018 5:59:51 PM EDT
[Last Edit: Ironmaker]
[#2]
Quote HistoryOriginally Posted By AKSnowRider:
Ab list it as .295 G7 in my kilo 2400 library..It only list it as the 142 grain Match King though.. For the pointed 142 grain Match king it list as .311 G7... Sierra SMK 0.264 123 gr Sierra TMK 0.264 130 gr Sierra SMK 0.264 142 gr Thanks edit: formatting tables sucks! |
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Posted: 12/5/2018 6:28:14 PM EDT
[#3]
I forgot about my AB app. It doesn't have the TMK's though.
Sierra SMK 0.264 123 gr 0.260 Sierra TMK 0.264 130 gr Sierra SMK 0.264 142 gr 0.301 |
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Posted: 12/5/2018 6:29:52 PM EDT
[#4]
Call Sierra, it's possible they have the info.
There are some other sources around. I think Byran Litz has analyzed most of the current bullets, and another good place to search is at Accurate Shooter. |
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Posted: 12/5/2018 7:13:51 PM EDT
[#5]
AB shows the Tipped Match King 130 grain @ .273 G7....
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Posted: 12/6/2018 11:56:29 AM EDT
[#6]
the 142 is around .313
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FL, USA
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Posted: 12/6/2018 1:25:27 PM EDT
[Last Edit: Reorx]
[#7]
FWIW, JBM puts the 142SMK @ .301 G7BC. The TMK will be a little higher... I'd go with TR's suggestion...
I've also heard (no first hand experience) from a Sierra rep (when I asked about G7BCs) that Sierra has some sort of ballistic software that lists G7 BCs... LINK Call Sierra for more precise details. |
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Posted: 12/6/2018 7:30:38 PM EDT
[#8]
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Posted: 12/6/2018 11:12:22 PM EDT
[#9]
Quote HistoryOriginally Posted By Ironmaker:
Thanks, this is what I am filling out. I used my AB app. https://www.AR15.Com/media/mediaFiles/57471/8157205B-799B-4612-A054-F9F2CB2DC12C_jpeg-763117.JPG Running that thru bullet drop I get 14.1 MIL and 4.9 mil @ 1K... for your first (123 grain )load.... |
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Posted: 12/7/2018 6:40:25 AM EDT
[#10]
Quote HistoryOriginally Posted By AKSnowRider:
OP, your numbers don't seem right...7.5mil of drop at 1K with 1.4 Mil of wind? Running that thru bullet drop I get 14.1 MIL and 4.9 mil @ 1K... for your first (123 grain )load.... Quote HistoryOriginally Posted By AKSnowRider:
Originally Posted By Ironmaker:
Thanks, this is what I am filling out. I used my AB app. https://www.AR15.Com/media/mediaFiles/57471/8157205B-799B-4612-A054-F9F2CB2DC12C_jpeg-763117.JPG Running that thru bullet drop I get 14.1 MIL and 4.9 mil @ 1K... for your first (123 grain )load....  Attached File Attached File |
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Posted: 12/7/2018 8:25:48 AM EDT
[Last Edit: AKSnowRider]
[#11]
Quote HistoryOriginally Posted By Ironmaker: Help me figure out what I’m doing wrong https://www.AR15.Com/media/mediaFiles/57471/541D0DAF-F40F-4EDC-9C3F-A56C4890E46C_png-763581.JPG https://www.AR15.Com/media/mediaFiles/57471/DCC0CD41-FD71-47C9-8B5A-D43A9DEFF549_png-763582.JPG  Attached File Attached FileETA..Thats pretty good numbers OP..my 300rum throwing a 230 Berger@3220 @ 1K with your weather shows 5.3 mil drop and 1.2 mil windage @ 2073 fps and 2194 for energy... |
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AL, USA
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Posted: 12/7/2018 4:41:09 PM EDT
[#12]
I use Brian Litz's book as a reference.
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Posted: 12/7/2018 7:45:18 PM EDT
[#13]
The best thing for you to do is start with the G1 and work yourself up a chart based on that.
JBM is an excellent resource that will allow you to input all the variables. http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi Once you shoot it at distance, check the bullet impacts vs. what's on your dope chart. Amend as needed. Make sure to shoot a few through the chrono that day and log the weather. Elevation and air temperature are critical. Depending on your location and types of powder you use, you may find the need to develop winter and summer loads. Something that was zeroed in August may not be the same zero in February. Critically a load that was hot, but safe in winter, may NOT be safe in the summer. Powders like RL17 are notorious for this. Sierra correctly provides the differing BCs, as it varies depending on speed. Fast loads (Say 3,400 + FPS) are better served initially working off a G1 BC. Slower stuff like a 6.5 Grendel (say 2,400 FPS) you should use the G7 BC. |
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Posted: 12/8/2018 11:34:54 AM EDT
[#14]
Quote HistoryOriginally Posted By nick1983:
The best thing for you to do is start with the G1 and work yourself up a chart based on that. JBM is an excellent resource that will allow you to input all the variables. http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi Once you shoot it at distance, check the bullet impacts vs. what's on your dope chart. Amend as needed. Make sure to shoot a few through the chrono that day and log the weather. Elevation and air temperature are critical. Depending on your location and types of powder you use, you may find the need to develop winter and summer loads. Something that was zeroed in August may not be the same zero in February. Critically a load that was hot, but safe in winter, may NOT be safe in the summer. Powders like RL17 are notorious for this. Sierra correctly provides the differing BCs, as it varies depending on speed. Fast loads (Say 3,400 + FPS) are better served initially working off a G1 BC. Slower stuff like a 6.5 Grendel (say 2,400 FPS) you should use the G7 BC. |
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Posted: 12/9/2018 8:02:19 PM EDT
[#15]
What difference does it make? The bullet is what it is and using a different B.C. scale does nothing to change it.
Using either scale will get you very close to final elevation at distance provided you have accurate velocity and atmospheric imputs. Once on target your final zeroes are always adjusted to center. It's very rare to mathematically be on target using either scale. |
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Posted: 12/9/2018 8:20:21 PM EDT
[#16]
Quote HistoryOriginally Posted By TeeRex:
BC changes with speed, but using G1 vs G7 has to do with bullet shape and has nothing to do with MV. |
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Posted: 12/10/2018 9:19:38 AM EDT
[#17]
Quote HistoryOriginally Posted By HighpowerRifleBrony:
Assuming same bullet shape, isn't G7 more precise for distances after transonic? Quote HistoryOriginally Posted By HighpowerRifleBrony:
Originally Posted By TeeRex:
BC changes with speed, but using G1 vs G7 has to do with bullet shape and has nothing to do with MV. Nobody with any sense is using G1 form factor bullets for long range if they have a choice. So why not use a BC that better matches your bullet shape. With a G7 and accurate inputs it is rare that your firing solution will be wrong. If it is wrong the user input inaccurate data. Most of my stuff goes well into transonic and my solver predictions match actual POIs. |
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Posted: 12/10/2018 9:25:04 AM EDT
[#18]
Quote HistoryOriginally Posted By borderpatrol:
What difference does it make? The bullet is what it is and using a different B.C. scale does nothing to change it. Using either scale will get you very close to final elevation at distance provided you have accurate velocity and atmospheric imputs. Once on target your final zeroes are always adjusted to center. It's very rare to mathematically be on target using either scale. |
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Posted: 12/10/2018 11:13:00 AM EDT
[#19]
I learned to dope wind by looking at conditions, flags, mirage, etc. Twenty years before Kestrel. Practice, lots of it, even when not shooting, helps to develop an eye for conditions.
Elevation come-ups are remembered or recorded based on past experience. Going to a match and winging it is going to backfire. All President 100 and NTI matches are no sighter tournaments. It helps in dicey conditions to wait until everyone else's first shot gets marked before squeezing yours off. If everyone underestimates or over compensates you'll see their first rounds all left or right of center. It lets you know the wind is more or less than it appears. |
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