Bullet stabillity question.

[4xforfun]

I have been tinkering with the Berger Balistics Twist Calculator. I am toying with the idea of a new slow twist BBL in either Dasher or 6-47L to shoot light bullets at near light speed for close range prairie dog hunting. I have twelveteen 1-8 twist tubes to shoot the 105 - 108 class bullets. When trying to shoot the lightweights in my used 1-8 twist tubes, my tests are showing either outright bullet blowup or impending blowup. I only tested at 100 yards, and think that some of the bullets that are actually getting to 100 may not make the next 200 yards!!! So, I am thinking about a dedicated dog killer in those two chamberings since I already have the brass and dies.

Now...the balistic calculator..... Can anyone tell me what twist people are shooting the 55 gr NBT and the 58 V-Max out of. Inputting all of the data on the calculator tells me that I would need at least a 1 - 12 twist tube to "properly" stabilize these bullets. Now, for those of you who have ever read my responces to other posts about which twist to stabilize which bullet, and someone says you "CAN'T shoot xyz bullet in an xx twist bbl because the twist calculator says it is only at xxx on the chart" and I respond with.."hey try it..it worked for me". BUT, I also usually state that if my intention from the start was to shoot xyz bullet, I would buy a faster twist right from the start to be absolutely sure it works. I shoot 200 Hybrids in a 1-12, I shoot 230 Hybrids in a 1-11 twist in sub zero weather. Didn't plan it that way..it just ended up "working out". I see a bunch of 1-13.5 and 1-14 twist tubes for sale, but, according to the twist calculator I am down under 1.10 with a 1-14 twist and a 55 gr NBT!!! What bullets do they shoot in a 1-14 twist. I don't even see a 6mm bullet that could possably work in a 14 twist with any cirtanty, which,if the calculator is correct, would be at least 1.50 on the chart.

Now, I would just simply buy a 1-10 to 1-12 twist and be done with it, but I can't find one that I can use. Anyone using a 1-13.5 - 1-14 twist tube out there. There must be lots of them, because everyone who sells bbls stocks them.

Thanks,
Tod

 

[JRS]

You'll usually find those twist rates in the point blank game in competition, shooting the 65 - 68 grain bullets. When I have a question about twist rate/stability, I always call the professor, Randy Robinett. Not only will he offer his expertise regarding the optimal twist rate, but also (if you ask) explain why a certain twist works best.

 

[BoydAllen]

I have shot them from 14 twist barrels loaded to the max in a 6PPC with no apparent problems. If you compare the numbers from the calculator with what is shot in short range benchrest, you will see a discrepancy.

 

[4xforfun]

I have shot them from 14 twist barrels loaded to the max in a 6PPC with no apparent problems. If you compare the numbers from the calculator with what is shot in short range benchrest, you will see a discrepancy.

Yep...just like the 22 caliber guys shooting the 55 NBT's in a 14 twist. How many hundeds of millions of 55 grn NBT's have been fired out of 223/22-250/220 etc.... with a 1-14 twist succesfully, yet, the Berger calculator says it was BELOW 1.0 on their stability calculator.
I guess that I would rather error on the fast side.....I can always go up in bullet weight, but, if the 55/58 grainers don't work I have nowhere to go! Our last 14 twist 22-250 AI with a 14 twist put the 55 NBT SIDEWAYS at 25 yards!!!

 

[JRS]

Talk to the "ballistic idiot". (515) 438-4010

 

[XBBR Shooter]

I see a bunch of 1-13.5 and 1-14 twist tubes for sale, but, according to the twist calculator I am down under 1.10 with a 1-14 twist and a 55 gr NBT!!! What bullets do they shoot in a 1-14 twist. I don't even see a 6mm bullet that could possibly work in a 14 twist with any certainty, which, if the calculator is correct, would be at least 1.50 on the chart.

Now, I would just simply buy a 1-10 to 1-12 twist and be done with it, but I can't find one that I can use. Anyone using a 1-13.5 - 1-14 twist tube out there. There must be lots of them, because everyone who sells bbls stocks them.

Thanks,
Tod

I think the Berger Twist Calculator is overly conservative. I shoot 65 gr V-Maxs(0.830"), Speer 70 TNTs (0.820") and Sierra 70 gr Blitzkings (0.892"), out of a 14" twist 6mmBR bench rifle with no problems. The 55 NBT (0.787") is short compared to these bullets.

I have found that if the stability factor is ~ 0.9-ish, it will work.

 

[JRS]

I think the Berger Twist Calculator is overly conservative. I shoot 65 gr V-Maxs(0.830"), Speer 70 TNTs (0.820") and Sierra 70 gr Blitzkings (0.892"), out of a 14" twist 6mmBR bench rifle with no problems. The 55 NBT (0.787") is short compared to these bullets.

I have found that if the stability factor is ~ 0.9-ish, it will work.

You can also swat a baseball with a tennis racket But not very well

 

[XBBR Shooter]

You can also swat a baseball with a tennis racket But not very well

Your comment makes no sense - the OP asked for comments from people that have shot light-ish (55gr NBT) bullets from a 13.5 or 14" twist barrel... I gave my experience with what he asked.

He said nothing about tennis or baseball.

 

[JRS]

Your comment makes no sense - the OP asked for comments from people that have shot light-ish (55gr NBT) bullets from a 13.5 or 14" twist barrel... I gave my experience with what he asked.

He said nothing about tennis or baseball.

That was in response to your Sg. claim of 0.9 The proverbial wreck, waiting to happen.

 

[4xforfun]

That was in response to your Sg. claim of 0.9 The proverbial wreck, waiting to happen.

True, but what is your responce to the hundred million 55 grn 22 cal NBT's succesfully shot out of a 1-14 twist with a SG of around .80?

Oh...by the way...GOLF is my game of choice!!

 

[XBBR Shooter]

That was in response to your Sg. claim of 0.9 The proverbial wreck, waiting to happen.

"The proverbial wreck, waiting to happen."

"A WRECK"... Really??? That much of a crisis??? You really get upset easily over little things.

First chart is the Berger rating evaluation of the 55gr Sierra BlitzKing at 3,800 fps in a 14" twist barrel - a combination that is very popular with chuck shooters (including myself) in 22-250's and .220 Swifts - some shooters have problems with it at 3,600 fps.





The second chart is the Berger rating evaluation of the 70gr Sierra BlitzKing at 3,300 fps in a 14" twist - a combination that is fairly popular with chuck shooters (including myself).





BOTH are rated as completely unstable, and both are under 0.9... and both shoot fine.

 

[4xforfun]

Well...it sounds like I could get a 13.5 or 14 twist to work. Thanks for the help. I won't order till next week, so if there is any more info you can let-R- Rip!!

 

[sofarfrome]

"...Our last 14 twist 22-250 AI with a 14 twist put the 55 NBT SIDEWAYS at 25 yards!!!"

This seems odd to me. I have fired literally thousands of 55gr bullets, including NBTs, out of 22 PPCs, 22 BRs, and 223s out of 14tw barrels of various manufacture, including factory barrels, at 3500FPS and above and have NEVER had an issue with stability. Even out to 300 yards on paper the bullet left perfectly round holes. Same holds true for the 6MM bullet up to 70gr in a 14tw. I remember having my first 6MM BR using Sierra 70gr match bullets in a Hart 14tw barrel and even light loads never went through any where close to sideways. I can't imagine why a 22 NBT out of a 22-250AI in a 14tw barrel would be throwing them sideways. Unless it was a 15tw and even then it still should shoot "square". I know people using 15tw barrels in a standard 22PPC and 53gr match grade bullets and they are tack drivers. Even in the middle of winter velocities from a 22-250AI should be enough to stabilize the 55gr NBT in a 14 twist.

 

[JRS]

There is a good reason why the original 14 twist M16 quickly moved to the 12 twist barrel.

 

[ebb]

After all this time I finally realize that the small .1s and ,0s Ive shoot with my 6PPC were not 5 shot groups at all, they were so unstable that 3 of my 5 shots must have missed the target. I am glad you all brought this to light and showed me that calculator! I'll be looking for an 8 twist barrel soon.

 

[JRS]

After all this time I finally realize that the small .1s and ,0s Ive shoot with my 6PPC were not 5 shot groups at all, they were so unstable that 3 of my 5 shots must have missed the target. I am glad you all brought this to light and showed me that calculator! I'll be looking for an 8 twist barrel soon.

Do you know why point blank Benchrest shooters choose the 13.5-14 twist barrels at the distances they shoot?

 

[ebb]

Cause they are the most accurate at those distances. Point blank shooters are driven by accuracy in every thing they do.

 

[Berger.Fan222]

Since they do not sell plastic tipped bullets, Berger has no reason to include the proper stability formula in their calculator. The JBM stability calculator has the right formula, where the length of the plastic tip is entered as a separate input (zero for untipped bullets).

The formula for plastic tipped bullets was also developed by Don Miller, who developed the formula for untipped bullets that the Berger calculator uses. I have found it to be a reliable indicator regarding twist rate requirements. By comparison, the Berger calculator predicts a lot of twist rates will not work with tipped bullets, when they really work great.

We shoot the 55 VMAX in a 1 in 14 twist all the time. It works great.

 

[NC308]

I have shot lots of 55 gr bullets in 14 twist swift with great success! They will work just fine. But I tried 60 gr and did not work so well!

 

[4xforfun]

I see a 27" 13.5 twist for sale. I think I will pull the trigger (pun intended) on that tube. Now I have another choice to make.......Dasher or 6-6.5-47L!!!

I guess it doesn't suck to have those choices!!!