Berger box twist recommendation vs twist rate calculator
- Thread starter RHux
- Start date
Yep, box twists ought to be considered as minimums beyond which those bullets just won’t work. Calculator gives you more options for your conditions/equipment/usage variables, the better to determine what will work best.
Folks I know shooting those two (I shoot 95 CH in a 6HAGAR spacegun, 1:7.5 twist 24” barrel) use 1:7.5 more often than something slower.
Folks I know shooting those two (I shoot 95 CH in a 6HAGAR spacegun, 1:7.5 twist 24” barrel) use 1:7.5 more often than something slower.
RHux,
spclark is correct. The new barrel twist rates are what is the MINIMUM barrel twist rate to stabilize that bullet. Previously we use an OPTIMUM barrel twist rate that was based on 59 degrees at sea level. When you read the BERGER TWIST RATE CALCULATOR keep in mind that the STABILITY FACTOR (SG) has to be below 1.0 for a bullet to be completely unstable ( I fudge this to 1.2). ANYTHING BETWEEN 1.0 TO 1.49 on the scale just reflects a compromised BC that is listed as a number and a percentage to use with the BALLISTIC CALCULATOR to get accurate data as far as wind drift ETC. The bullet will still be stable to the end of its flight. Hope this helps. If you have any more questions please feel free to contact us at any time!
Good clarity, it seems to me if you are shooting a 6mm Berger 105 gn or 115 gn
bullet shoot with a 7 tw barrel.
bullet shoot with a 7 tw barrel.
105’s work fine in 1:7.5’s while 1:7 might be too fast if using a mid- to high-volume case design in >20” barrel with resulting high muzzle velocities.
I blew up several 115’s years ago in 1:8 Schneider chambered for 6XC that came with the T2k I’d bought so that’s too slow. 1:7.5 might work but I’d lean towards 1:7 too for the 115VLD & develop load for accuracy not ultimate fps #’s.
No issues with either the new Berger 105 or 115 Hunting bullet at 500yds in my 6 Dasher. To date, the Berger 115n Hunting bullet clearly shoots the best groups I have ever shot with a factory bullet. Will be testing both in the same gun/barrel in a back to back comparison. Will shoot all within 1 hr in light conditions. As long as I have been shooting, my powder charge or primer has not changed. Not saying it is best procedure, just my process. I just tweak my tuner to adjust for air density. All my current group testing has been at “touch”. Tuning is with a couple of small tweaks on the tuner. Will be shooting more on Friday and post the results.
Ben
Ben
Dusty Stevens
Shiner
At least theyre putting them on there and updating as testing evolves. Great job. Even different lots need tested in your setup and no matter what your calculator says you still gotta test em
Seems like the most accurate way to list this info would be a rpm range. Then people could use the calculator to determine what rpm they will generate with their twist and charge. If you have the right twist but push them hard enough to come appart then a less than average reloader might not know the reason for the problem. Am I off or does this make sense?
Please do! I'd be interested in seeing your results (even though I haven't shot anything but 308WIN/155.5 Fullbores since 2016)!
NEVER a bad idea.
Yes you do!
One needs to be careful to check math results when calculating this though. It's easy to forget to change value tags when plugging in velocity per second when the other time-dependent factor is rotations per minute.
This thread makes me want to check into the differences between Berger's old 115 VLD - the bullet I tried and watched form grey puffs out of that 1:8 back in 2005 - and what folks are saying is now their 115 Hunting (#24530) offering in their present line-up.
To my understanding they're the same thing? That the current Target bullet, their #24430 Target 115 - features heavier jackets than the Hunting line's 115, which used to be the only 6mm 115VLD offered?
DirtySteve
Gold $$ Contributor
More twist is gooder if shooting where the bullet will get close or fall below transonic speed.
This according to Litz.
This according to Litz.
True enough but watch velocity: faster twist plus faster fps can and does cause problems besides blow-ups. The longer the bullet the more likely the chance a faster twist will cause any instability to affect accuracy.
To my mind it’s prudent to accept a lower fps that gains back stability that’d otherwise be lost. Easier to back off on load levels than source, acquire & fit a (slightly) slower twist barrel.
Liven The Dream
Gold $$ Contributor
I just received a new box of Berger 30 cal. 155 HB the Box states 1-11 twist .
I won a Broughton Barrel ? I called a stated I wanted a 32" to finish Palma Barrel .
I told the gentlemen on the phone the Type Bullets I would be shooting Burger 155 HB , 155.5 and Sierra 2156's .
The reply was 5C 1-11 for Sure …. Come the New Year and instillation I will see ?
I won a Broughton Barrel ? I called a stated I wanted a 32" to finish Palma Barrel .
I told the gentlemen on the phone the Type Bullets I would be shooting Burger 155 HB , 155.5 and Sierra 2156's .
The reply was 5C 1-11 for Sure …. Come the New Year and instillation I will see ?
Bullet RPM FORMULA:
MUZZLE VELOCITY X 720 = X. X divided by barrel twist rate = RPM.
3400FPS X 720 = 2,448,000. 2,448,000 divided by 7 ( 1-7 twist) = 349,714 RPM
General rule of thumb is that if your muzzle velocity is close to or over 3400FPS and your bullet RPM is close to or over 300,000 . Either one or both could cause bullet failure of ANY cup and core style bullet. Add to this barrel lengths over 28 inches , defects in the barrel ( chipped land ETC), fire cracking of the throat, excessive barrel twist rate , ETC. and you just add to the problem. Hope this helps.
So is there an ideal band for rpm like 200-250k rpm for heavy in caliber bullets. Be sweet if there was a chart or graph for this.
When referring to the Berger 105 in your analysis and questions you need to be more specific. The Berger 6mm 105 comes in 105 Target BT, 105 Target VLD, 105 Target Hybrid and 105 VLD Hunting. To get the proper stability and twist rate from the Berger Twist Rate Calculator and advice from forum members you will need to refer to the proper bullet. Several times in prior posts above people just refer to the Berger 105.
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