Oval bullet holes

Pete Wass

Pete Wass

Well-known member
I had an interesting occurance the other day at the range. I had a 300 yd match coming up so I decided to try to find more stability in the wind; which we had yesterday.

I have a box of 125g 30 cal bullets on the 1.080 jacket. I thought they might be a winning combination with my new barrel. I loaded up my usual test group of rounds and went to the range.

I shot the test and it was a failure; no groups under 3/4" and ragged. I retreived the target and could see that all the holes were oval shaped. I realized the bullets werent's stable. The barrel is a 1-18 twist. I expected it to stabalize those bullets but I guess I found the limits of the twist?
 
Pete

The temps back in Maine are moderate now back off your winter powder load and try again. Keep everything else the same.

Stephen Perry
 
Twist

Pete Wass said:
I had an interesting occurance the other day at the range. I had a 300 yd match coming up so I decided to try to find more stability in the wind; which we had yesterday.

I have a box of 125g 30 cal bullets on the 1.080 jacket. I thought they might be a winning combination with my new barrel. I loaded up my usual test group of rounds and went to the range.

I shot the test and it was a failure; no groups under 3/4" and ragged. I retreived the target and could see that all the holes were oval shaped. I realized the bullets werent's stable. The barrel is a 1-18 twist. I expected it to stabalize those bullets but I guess I found the limits of the twist?
Click to expand...

Not knowing your velocity, my best guess would be a 1:14 twist for a 125 gr .30 caliber bullet that is 1.080" long. See: A New Rule For Estimating Rifling Twist, An Aid To Choosing Bullets And Rifles by Don Miller (Precision Shooting, March 2005). There are two subsequent articles by Don Miller; The New Twist Rule Part I: Tests Against Experimental Data (PS, Feb ’08) and The New Twist Rule Part II: Examples, Stability, Questions and Other Estimation Methods (PS, Mar ’08). nhk
 
Pete, mike all of your bullets

They are oval. It happens when the temperatures get below -100 degs like up there in the summer in Maine or the North Pole where you live. Or maybe Pluto.:cool:

Rooah.
 
You can try this site. http://www.uslink.com/~tom1/twistrate.htm Using the info you supplied you would have to drive that 1.080 bullet about 3428 fps to stabilize in an 18 twist barrel. It its a 30BR not sure you can get there. Maybe with a 308 Win and Lapua cases.

Donald
 
Just wne ya think everything is gonna go wrong

IT DOES ! :)

Being Ignorant of "tis rates" (more ebonics), I ASSUMED the reverse were true of what actually were.
 
Bullet length is more important than weight for bullet stability. A few years back someone was supposedly making heavy .22 bullets for NRA across the course shooting with some sort of compressed powdered (so it wouldn't be AP) tungsten or tungsten alloy core that as I remember was the same length as the 69 gr SMK, but weighed 87 gr as I remember. These bullets were supposedly stable to 600 yd with then standard twists in .223's/5.56's.

The site <(http://www.uslink.com/~tom1/twistrate.htm)> is for black powder cartridge rifles which all fire cast lead bullets which is why it's likely some different than a formula for jacketed bullets.
 
Stability

Larry Elliott said:
Bullet length is more important than weight for bullet stability.
Click to expand...

True, added length requires a faster twist. The Greenhill formula and Velocity formula come up short in twist estimations because thery are based on lead bullets. The stability for the density of lighter bullet materials and less mass per length is better calculated by the Don Miller Twist Rule, which takes into account the mass of the projectile.

Example: The Barnes .224 36 gr Varmint Grenade (no lead) is ~.698" long and can be fired at 3600 fps from a .223 Rem. The Velocity formula gives you a 1:15 twist, the Greenhill formula gives you a 1:12 twist, Which has a marginal stability factor of about 1.0 with The Miller Twist Rule. If you use the JBM link and calculate it for optimum stability you need a 1:10 twist (1.4 stability factor). The first review of the 36 gr VG I read was shot with 1:8 and 1:9 twists with good accuracy. I couldn't get them to group to my satisfaction in a 1:12 twist, but could in a 1:9 twist.

A 53 gr Sierra MK (lead, with flat base) is about .703" long, close to the same length as the VG, but about 1.5X heavier. At 3100 fps the Velocity formula gives you a 1:13 twist, the Greenhill formula a 1:12 (round down) twist, and the Miller Twist Rule a 1:12 twist to be optimally stabile.

I would conclude that to mean stability increases with an increase in mass per a given length and a less dense bullet of the same length requires more twist to stabilize it. nhk
 
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