# Thread: Now I am a bit confused.

1. ## Now I am a bit confused.

In a quick exchange about bullets and premium twist rates in a previous thread, I was told that some bullets that I had had a good result in reloading would not be the best. So I thought I would have a quick look and found this from Berger
http://www.bergerbullets.com/twist-rate-calculator/
It was quite nice because it works if you input your own data and then goes on to recommend twist rates for your chosen bullet based on length of bullet,BC,muzzle velocity, barrel twist etc.
Now I typed in the stats for the bullet that was poo-pooed and it says that it will be very stable. Okay I thought.
Then I typed in the stats for the heavier bullet and it says that it will only be marginally stable and the twist rate will be completely wrong.
Now I have a 1:10" twist for a .257 Roberts which seems to be their given twist rate. However on crunching some random bullet manufacturers numbers into the calculator it has left me somewhat puzzled.
Now I'm not anal about this sort of stuff because if it shoots then I'll use it but why the disparity in information.

2. For any given bullet design, a heavier bullet will be longer than a lighter bullet. The length, not the weight, dictates twist rate. But two bullets of the same weight can be different lengths.

Let's consider a a traditional bullet shape, a flat based spitzer. Let's say a .243 100 grain bullet. For argument's sake it's an inch long, and 3/4 of that inch is in barrel contact. A 1:10" twist barrel is designed to stabilize that bullet.

Now let's change the base to a boat tail and the nose to a long tapering hollow point, with only 1/4 inch in contact with the barrel. Let's just say that makes our 100g bullet have a length of 1 1/4 inches. Suddenly, our 100g bullet can't be stabilized by our 1:10" twist barrel, we need a 1:9 or even a 1:8 twist becuase the longer bullet has to be spun faster.

Berger bullets are long for their mass. If you stick with traditional bullets, not very low drag bullets, your 1:10 should be fine.

-JMS

3. Got this link in my favourites www.ShootForum.com - Bullet Database

Very handy. If you're having good results with a heavier than normal bullet then Use it. It may not be spinning as fast as is ideal though so test it out at longer ranges and see if it keyholes.
It'll be travelling faster due to the slower twist anyway

4. looks good on paper but.....

no one has told the bullets!!

I have a load for my .222 1:14 twist shooting 60gr flatbase bullets
here-say tells you that they won't work
Berger says they will...it goes on to say that they are VERY stable and that even at extended velocities that they will stabilise

simply not the case
above and below a moderate charge they were wildly innaccurate (like 6" groups inaccurate!)
in the sweet spot they touch holes

There are 1000's of .243's out there shooting 100gr loads with ease, some shoot 105gr Geco factory with ease also
some turn into shotguns

only your barrel and bullet combo will show what works

5. I worked with a Remington engineer to develop data for the 30 Rensi back in 1999/2000. The cartridge is an necked down 338L. The rifle has an M24 5R barrel with a twist of 1:11.3. I developed loads for bullets ranging from 200 to 155grs. Although convention wisdon says I could not get the 200gr SMKs to stabilize with that twist rate it shoot s them extrememly well. I think the reason behind this was that I was able to get them out of the 24 barrel at over 2900fps using IMR7828. In some cases if you drive a bullet fast (or slow) enough you can compensate for the barrel twist. The testing was documented in an article published in the April 2000 issue of Tactical Shooter magazine. If you would like a copy PM me with an email address and I will send you a copy.

SS

6. Originally Posted by MARCBO
if you drive a bullet fast (or slow) enough you can compensate for the barrel twist.
exactly what I found
groups started at 4-5" shrinking by about an inch down to an inch with each 02.gr increment
and then increasing by 2" each step above that
I stopped when they started reaching the edge of the target!

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