Forums
New posts
Search forums
What's new
Articles
Latest reviews
Author list
Classifieds
Log in
Register
What's new
Search
Search
Search titles and first posts only
Search titles only
By:
New posts
Search forums
Menu
Log in
Register
Install the app
Install
Forums
Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Hammer ballistic coefficient tests...
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Message
<blockquote data-quote="Pdvdh" data-source="post: 2613423" data-attributes="member: 4191"><p>I've used LabRadar velocity decay data from the first 80-100yds of bullet fight to calculate the BC values of every bullet I shoot in these calibers (.224, .257, .284, .308, and .338). Been doing this ever since shortly after I purchased the LabRadar unit, about 5 years ago.</p><p></p><p>After reviewing the LabRadar data, and ensuring the pool of velocity decay data is reliable and in close agreement for each bullet fired, this method isn't much more complicated than back calculating a BC value based on long range bullet drops. And the BC values will be more accurate than BCs based on bullet drop, because the human error associated with accurate bullet placement, and the error due to ambient environmental conditions on long range bullet drops, have been removed from the BC determinations.</p><p></p><p>The equipment required for my method is 1) LabRadar to collect velocity decay data, 2) Kestrel to collect reliable station atm pressure / temperature / humidity, 3) a reliable ballistics program.</p><p></p><p>The knowledge requirements required for my method include 1) an ability to review, identify, and discard any faulty LabRadar velocity decay data, and 2) competency with the ballistics program.</p><p></p><p>The extra cost compared to relying solely on bullet drops for BC determination are the LabRadar. And if you're a reloader, and half-serious about long range shooting and hunting, you ought to have a LabRadar anyhow, in my opinion.</p><p></p><p>One thing I've determined in the past several months is the significant affect barrel twist rate can have on bullet BC value. This became obvious while testing identical bullets from two different rifles. Both rifle chambers were cut with the same chamber reamer. Only significant difference between the rifles are the barrel manufacturer and barrel twist rates. One barrel a 9.4 twist and the other a 8.5 twist. I see a substantial difference in bullet BC value from the two different barrels. The faster twist barrel yielding the higher bullet BC values. I find a much bigger difference in BC value than the ~2% rule of thumb difference Bryan Litz has referenced, from his bullet BC measurements in different twist rate barrels. Dunno if Bryan is still sticking with the 2% figure or not...</p><p></p><p>A side benefit of my process? If you receive a defective batch of bullets that will not stabilize in flight! I received some defective bullets one year ago that were imprinting 22" groups at 280yds from a rifle that was shooting better than 1/2moa precision with 5 other bullets. The bullets were flying with such poor stability that my BC values were 1/2 the manufacturer's stated BC value. Eventually the manufacturer identified the problem and I received some replacement bullets. I suspect I'd measure similarly reduced BC values from any bullet that was poorly stabilized in flight.</p><p></p><p>Some bullets I test are very close to the manufacturer's stated BC value. Some values are 6% higher than advertised. Some have been 35-38% lower than advertised. More BC values are calculated lower than advertised, than higher. Some BC values are so low from my barrels that I quickly dismiss use of the bullet for any ranges past ~450yds.</p><p></p><p>I've learned calculating a BC value with my methods is very repeatable over time. I consider my calculated BC values accurate to within ~ 1.5% from my barrels. As over time, using different batches of LabRadar velocity decay data for the same bullet, from the same rifle, I experience calculated BC values with maximum differences of ~1.5%.</p></blockquote><p></p>
[QUOTE="Pdvdh, post: 2613423, member: 4191"] I've used LabRadar velocity decay data from the first 80-100yds of bullet fight to calculate the BC values of every bullet I shoot in these calibers (.224, .257, .284, .308, and .338). Been doing this ever since shortly after I purchased the LabRadar unit, about 5 years ago. After reviewing the LabRadar data, and ensuring the pool of velocity decay data is reliable and in close agreement for each bullet fired, this method isn't much more complicated than back calculating a BC value based on long range bullet drops. And the BC values will be more accurate than BCs based on bullet drop, because the human error associated with accurate bullet placement, and the error due to ambient environmental conditions on long range bullet drops, have been removed from the BC determinations. The equipment required for my method is 1) LabRadar to collect velocity decay data, 2) Kestrel to collect reliable station atm pressure / temperature / humidity, 3) a reliable ballistics program. The knowledge requirements required for my method include 1) an ability to review, identify, and discard any faulty LabRadar velocity decay data, and 2) competency with the ballistics program. The extra cost compared to relying solely on bullet drops for BC determination are the LabRadar. And if you're a reloader, and half-serious about long range shooting and hunting, you ought to have a LabRadar anyhow, in my opinion. One thing I've determined in the past several months is the significant affect barrel twist rate can have on bullet BC value. This became obvious while testing identical bullets from two different rifles. Both rifle chambers were cut with the same chamber reamer. Only significant difference between the rifles are the barrel manufacturer and barrel twist rates. One barrel a 9.4 twist and the other a 8.5 twist. I see a substantial difference in bullet BC value from the two different barrels. The faster twist barrel yielding the higher bullet BC values. I find a much bigger difference in BC value than the ~2% rule of thumb difference Bryan Litz has referenced, from his bullet BC measurements in different twist rate barrels. Dunno if Bryan is still sticking with the 2% figure or not... A side benefit of my process? If you receive a defective batch of bullets that will not stabilize in flight! I received some defective bullets one year ago that were imprinting 22" groups at 280yds from a rifle that was shooting better than 1/2moa precision with 5 other bullets. The bullets were flying with such poor stability that my BC values were 1/2 the manufacturer's stated BC value. Eventually the manufacturer identified the problem and I received some replacement bullets. I suspect I'd measure similarly reduced BC values from any bullet that was poorly stabilized in flight. Some bullets I test are very close to the manufacturer's stated BC value. Some values are 6% higher than advertised. Some have been 35-38% lower than advertised. More BC values are calculated lower than advertised, than higher. Some BC values are so low from my barrels that I quickly dismiss use of the bullet for any ranges past ~450yds. I've learned calculating a BC value with my methods is very repeatable over time. I consider my calculated BC values accurate to within ~ 1.5% from my barrels. As over time, using different batches of LabRadar velocity decay data for the same bullet, from the same rifle, I experience calculated BC values with maximum differences of ~1.5%. [/QUOTE]
Insert quotes…
Verification
Post reply
Forums
Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Hammer ballistic coefficient tests...
Top