5.56/.223 bullet weight in a 1:9 barrel
- Thread starter w squared
- Start date
Do they keyhole on you? What are the dimensions of the Barnes 70gr in relation to non-copper bullets? Do they need to be longer than FMJ/BTHP of an equivalent weight due to the difference in density? Will this w squared dude ever stop asking questions????
Yes, Barnes keyholes pretty badly at 100 yards. I never saw other 70gr bullets, so no idea how much longer it is.
Here, all I used in my gun, left to right: Hornady V-Max 60gr, Hornady SP 60gr, Sierra SP 55gr, Hornady bulk 55gr SP, Barnes tripple shock 70gr
Well, I guess that would explain all the keyholing out of a 1:9....
I know that this is far from accurate, but looking at the picture, it does seem to me that the lower density of the copper must necessitate a longer bullet to get up to that 70 grain weight on the Barnes.
I know that this is far from accurate, but looking at the picture, it does seem to me that the lower density of the copper must necessitate a longer bullet to get up to that 70 grain weight on the Barnes.
Hi
Barnes goes into a long song and dance about how the copper bullets are not necessarily longer than other bullets. What they say is true, but it sort of misses the point.
The standard grains to twist stability stuff all *assumes* a solid bullet. Any time you make it long an hollow, or out of something other than lead you need to do the real (length based) calculations. Most people think in terms of 72 grains is stable in 1:9 barrels, not in what ever the magic length is ...
Bob
Barnes goes into a long song and dance about how the copper bullets are not necessarily longer than other bullets. What they say is true, but it sort of misses the point.
The standard grains to twist stability stuff all *assumes* a solid bullet. Any time you make it long an hollow, or out of something other than lead you need to do the real (length based) calculations. Most people think in terms of 72 grains is stable in 1:9 barrels, not in what ever the magic length is ...
Bob
using the formula below, the max length projectile for a 1/9 twist should be about.8326 below 3000fps and inch long increasing to about 1" long above that. The reason being the increased gyro forces due to faster rotation.
One of the first persons to try to develop a formula for calculating the correct rate of twist for firearms, was George Greenhill, a mathematics lecturer at Emmanual College in Cambridge, England. His formula is based on the rule that the twist required in calibers equals 150 divided by the length of the bullet in calibers. This can be simplified to:
Twist = 150 X D²/L
Where: D = bullet diameter in inches L= bullet length in inches
This formula had limitations, but worked well up to and in the vicinity of about 1,800 f.p.s. For higher velocities most ballistic experts suggest substituting 180 for 150 in the formula. The twist formulas used in the Load From a Disk program, featured at this web site, uses a modified Greenhill formula in which the "150" constant is replaced by a series of equations that allow corrections for muzzle velocity from 1,100 to 4,000 ft/s (300 to 1200 m)
One of the first persons to try to develop a formula for calculating the correct rate of twist for firearms, was George Greenhill, a mathematics lecturer at Emmanual College in Cambridge, England. His formula is based on the rule that the twist required in calibers equals 150 divided by the length of the bullet in calibers. This can be simplified to:
Twist = 150 X D²/L
Where: D = bullet diameter in inches L= bullet length in inches
This formula had limitations, but worked well up to and in the vicinity of about 1,800 f.p.s. For higher velocities most ballistic experts suggest substituting 180 for 150 in the formula. The twist formulas used in the Load From a Disk program, featured at this web site, uses a modified Greenhill formula in which the "150" constant is replaced by a series of equations that allow corrections for muzzle velocity from 1,100 to 4,000 ft/s (300 to 1200 m)
