Phil Rizzo
Well-Known Member
Your testing helps some of us curious and maybe lazier shooters settle arguments!
Thank You for the published results.
Thank You for the published results.
Episode 2: 6.5 PRC 26" to 18" barrel velocities test by James Eagleman
- Thread starter Barbourcreek
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Hugnot
Well-Known Member
Sure looks like the AB guys use the olde process that Miller designed.
Going to the AB site and looking at an example:
Then taking the data- looks like a .308 175 Sierra MK, bullet length 1.240, 11.25 twist, 2650 fps, 59 F, 29.92 in. Hg, producing a Sg of 1.91
The Miller process on Excel produces:
Sg AB = 1.91, Sg Via Excel/Miller = 1.91
Both are equal, rounded off to 2 places. Very unlikely two different methods would produce the same results, making me believe AB uses the Miller process.
The Miller process is a Sg estimator, the math is involved but not complex (like add, subtract. divide, & exponential) as seen in the Excel spread sheet.
Going back to the example shown on post #1. I could not duplicate the Sg value for the 147 6.5 ELD 2863 unless I plugged in a temperature of 99 degrees and omitted the plastic tip, entering 0 for tip length. The Sg values were identical to those shown in post #1:
Sg = 1.68 for 30 in of Hg pressure
Sg = 2.02. for 25 in of Hg pressure
I am assuming the bullet used in post #1 is the 147 gr. 6.5 Hornady ELD as I was able to exactly duplicate Sg values of 1.68 & 2.02 but with temperatures of 99 deg. F & no plastic tips (tip length 0)
Barometric pressures in Montana are usually between 29 & 30 inches of Hg. A pressure of 25 inches Hg recorded in Montana, at a place having boots on the ground would indicate real bad hunting weather where the animals would be seeking shelter & not moving. Hunting in a blizzard or super cell is tough.
The AB bullet library should contain the 147 ELD bullet that has a plastic tip. Possibly the plastic tip was omitted in determining bullet length.
Documentation regarding bullet length was provided in my previous post, #9.
I was unable to resolve the Sg values shown in post #1.
The AB Sg values are too low as the plastic tip was not subtracted from bullet length. Increased Sg values would improve bullet ballistics & efficiency.
Going to the AB site and looking at an example:
Then taking the data- looks like a .308 175 Sierra MK, bullet length 1.240, 11.25 twist, 2650 fps, 59 F, 29.92 in. Hg, producing a Sg of 1.91
The Miller process on Excel produces:
Sg AB = 1.91, Sg Via Excel/Miller = 1.91
Both are equal, rounded off to 2 places. Very unlikely two different methods would produce the same results, making me believe AB uses the Miller process.
The Miller process is a Sg estimator, the math is involved but not complex (like add, subtract. divide, & exponential) as seen in the Excel spread sheet.
Going back to the example shown on post #1. I could not duplicate the Sg value for the 147 6.5 ELD 2863 unless I plugged in a temperature of 99 degrees and omitted the plastic tip, entering 0 for tip length. The Sg values were identical to those shown in post #1:
Sg = 1.68 for 30 in of Hg pressure
Sg = 2.02. for 25 in of Hg pressure
I am assuming the bullet used in post #1 is the 147 gr. 6.5 Hornady ELD as I was able to exactly duplicate Sg values of 1.68 & 2.02 but with temperatures of 99 deg. F & no plastic tips (tip length 0)
Barometric pressures in Montana are usually between 29 & 30 inches of Hg. A pressure of 25 inches Hg recorded in Montana, at a place having boots on the ground would indicate real bad hunting weather where the animals would be seeking shelter & not moving. Hunting in a blizzard or super cell is tough.
The AB bullet library should contain the 147 ELD bullet that has a plastic tip. Possibly the plastic tip was omitted in determining bullet length.
Documentation regarding bullet length was provided in my previous post, #9.
I was unable to resolve the Sg values shown in post #1.
The AB Sg values are too low as the plastic tip was not subtracted from bullet length. Increased Sg values would improve bullet ballistics & efficiency.
polloxtroy85
Member
Thank you for this wonderful work!
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