MAX GRAIN 1:10 16" BARREL STABLIZE

[ryu_sekai]

What is the heaviest .223 grain a 16" 1:10 twist barrel can stablize?

[AlleninAlaska]

What caliber? 1-10 is fairly standard in 308 caliber and you can shoot 180-200 grain bullets quite well. The only problem with a 16" barrel is having to use fast burning powders to achieve as close to possible complete burning of said powder. Too short for slow burning powders to achieve good burn.

[ryu_sekai]

.223

[TRAP55]

62

[LDBennett]

ryu_sekia

The "correct" bullet according to the established formula is dependent on the diameter and the bullet length. As any given weight of bullet can have various lengths dependent on the design of the nose and tail, it really is a function of the exact bullet you use, by manufacturer. The formula is the rate of twist in inches equals 150 times the diameter squared divided by the measured length (both in inches). Below is a table of a few 223 bullets I did based on the above formula. Sorry the formating does not come out right but the first line is the key to the data with the last number being the twist. As can be seen it is not just the weight (not even in the formula) but the form factor. The twist is the slowest twist that will work (big numbers are slower twist rates). You can use a twist too fast and the bullets will explode as they leave the barrel, especially thin walled varmit bullets.

Mfg Wt. Length Dia. Twist-inches
Sierra 52 HPBT Match 0.755 0.224 10.0
Sierra 53 HP Match 0.755 0.224 10.0
Sierra/Win 55 FMJBT 0.765 0.224 9.8
Sierra 60 HP 0.785 0.224 9.6
Sierra 63 SP 0.765 0.224 9.8
Sierra 69 HPBT Match 0.890 0.224 8.5
Speer 52 HP 0.704 0.224 10.7
Speer 62FMJBT 0.910 0.224 8.3
Speer 70 Spitz 0.790 0.224 9.5
Hornady 55 FMJBT 0.765 0.224 9.8
Hornady 60 SP/HP 0.840 0.224 9.0
Hornady 68 HPBT Match 0.900 0.224 8.4
Hornady 52 A-MAX 0.735 0.224 10.2
Hornady 75 A-MAX Match0.895 0.224 8.4
Hornady 70 SP 0.795 0.224 9.5
Hornady 55 V-MAX 0.765 0.224 9.8
Hornady 60 V-MAX 0.825 0.224 9.1
Hornady 52 HPBT 0.630 0.224 11.9
Hornady 53 HP 0.645 0.224 11.7
Hornady 68 HPBT 0.700 0.224 10.8
Hornady 75 HPBT 0.895 0.224 8.4

[CountryGunsmith]

Here is the 'Greenhill Formula' for determining optimum twist rate.

Twist = 150 (d/r)

d is the bullet diameter
r is the length of the bullet divided by the diameter

Most AR shooters are opting for the 1:9 twist since it will shoot all but the heaviest or lightest bullets well. This would cover 90%+ of commercial ammunition. 1:10 would give similar results.

[LDBennett]

Countrygunsmith:

Or with a little algebra:

Twist = 150 times the diameter squared divided by the length of the bullet

I just wanted to make that clear to the user as at first glance our formulas may appear to be different which they are not. Thanks for the name "Greenhill" which I could not remember.

LDBennett

[ryu_sekai]

Originally Posted by TRAP55

62

if its 62 then why does the bullet manufacter say 1:10 for their 68 grain?


thanks for the help guys( Great Table/Chart!!!)

[LDBennett]

ryu_sekai:

Did you read my post? The twist for any given bullet is dependent on the bullet shape not the weight. Long skinny bullets need lots of RPMs (short twist rate) to stabilize so they don't wobble on the way to the target. The Greenhill formula was developed a long time ago to characterize what twist rate is needed and was based on practical experience and experimentation.

LDBennett

[TRAP55]

if its 62 then why does the bullet manufacter say 1:10 for their 68 grain?

Sierra 63 SP 0.765 0.224 9.8
Hornady 68 HPBT 0.700 0.224 10.8
Besides bullet weight, do you see something different here? LD explained it better than I could though.

[ryu_sekai]

Originally Posted by LDBennett

ryu_sekai:

Did you read my post? The twist for any given bullet is dependent on the bullet shape not the weight. Long skinny bullets need lots of RPMs (short twist rate) to stabilize so they don't wobble on the way to the target. The Greenhill formula was developed a long time ago to characterize what twist rate is needed and was based on practical experience and experimentation.

LDBennett

i did read your post i was asking other guy who said 62 was max grain

your post helped me alot thanks again great chart