I shoot F-Class Open downunder and have always been one to accept and use new technology if it could lead to increased accuracy and score.
I have very much appreciated Bryan Litz's contribution to ballistics and his books are well written and understandable by shooters like me. All my barrels, loads and bullets were based on SG = 1.4 and the stability factor may vary from 1.3 to 1.5 depending on the bullet I use.
SG = 1.4 was last years value and now Bryan thru testing has come up with 1.5 as being the preferred value, as it provides max BC as well as stability. All good stuff and a big thank you to Bryan!
My new barrels will be bought with twist rates that provide SG = 1.5 but so far I have not experienced any first hand stability problems shooting 1.3 to 1.5. Temperatures in Oz always have a plus sign in front of them for competitions and are mostly shot at not much above sea level.
Recently my shooting buddy has been developing a 7mm Dakota load for the new hyper high BC, Berger 195gr hybrid bullet. We both shoot F-Open and he wants this gun for long range work out to 1200 yards. The barrel is a 32" Krieger 5R, 8.5 twist rate, 1.25" parallel with a Kelby F-Class action.
He is experiencing bullet blow ups at 3020fps and we are wondering if the SG = 1.5 requirement of a 8.5 twist rate is responsible. At 3020fps the bullet is spinning at approx 255,800 rpm. Have Berger Bullets or anyone else performed tests on the mechanical integrity of bullets versus spin rate?
Dropping the velocity to 2900fps, (232,000 rpm) has reduced the bullet blow ups but still the occasional bullet just turns into a grey cloud on its way to the target. He has a identical barrel and chamber in 9 twist that will be tested sometime soon. It will be interesting to see if over revving the bullet is the cause. Maybe the 9 twist barrel will get the centrifugal forces back under control.
Can anyone contribute data to bullet rpm and mechanical breakdown? Could be interesting for a certain Berger Ballistician to workout the failure rpm of the bullet?
Ian
I have very much appreciated Bryan Litz's contribution to ballistics and his books are well written and understandable by shooters like me. All my barrels, loads and bullets were based on SG = 1.4 and the stability factor may vary from 1.3 to 1.5 depending on the bullet I use.
SG = 1.4 was last years value and now Bryan thru testing has come up with 1.5 as being the preferred value, as it provides max BC as well as stability. All good stuff and a big thank you to Bryan!
My new barrels will be bought with twist rates that provide SG = 1.5 but so far I have not experienced any first hand stability problems shooting 1.3 to 1.5. Temperatures in Oz always have a plus sign in front of them for competitions and are mostly shot at not much above sea level.
Recently my shooting buddy has been developing a 7mm Dakota load for the new hyper high BC, Berger 195gr hybrid bullet. We both shoot F-Open and he wants this gun for long range work out to 1200 yards. The barrel is a 32" Krieger 5R, 8.5 twist rate, 1.25" parallel with a Kelby F-Class action.
He is experiencing bullet blow ups at 3020fps and we are wondering if the SG = 1.5 requirement of a 8.5 twist rate is responsible. At 3020fps the bullet is spinning at approx 255,800 rpm. Have Berger Bullets or anyone else performed tests on the mechanical integrity of bullets versus spin rate?
Dropping the velocity to 2900fps, (232,000 rpm) has reduced the bullet blow ups but still the occasional bullet just turns into a grey cloud on its way to the target. He has a identical barrel and chamber in 9 twist that will be tested sometime soon. It will be interesting to see if over revving the bullet is the cause. Maybe the 9 twist barrel will get the centrifugal forces back under control.
Can anyone contribute data to bullet rpm and mechanical breakdown? Could be interesting for a certain Berger Ballistician to workout the failure rpm of the bullet?
Ian
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