Which twist rate for heaver projectiles?

[AMT7]

Admittedly dyslexia plauges me since birth. Just having trouble remembering and as to why helps.

Which twist rate 1:7 or 1:9 barrel is best for heavier 75-77gr 223/ 5.56x45 projectiles in 14.5" barrels? Think I had stated once 1:9 when negociating a deal but am thinking have it backwards after talking to a friend.

 

[swampratt]

Most say faster twist for heavier projectile.

 

[AMT7]

Most say faster twist for heavier projectile.

1:7 then. Would the only disagreeing ones have oddity issues?
The engineering data by now should be well established.

 

[swampratt]

Heavier or longer bullet is sometimes the debate.
You go 1:7 and it can over spin the lighter ones and MoBoost has done that and watched the bullet get out of the barrel and down range in mid air watch it vaporize.

Do a trajectory calculation and see the drop vs distance on the bullets you plan to use.
Heavier bullets get pushed less by wind..

 

[Calamity Jake]

Fast twist, heavy bullet!!!!

Slow twist, light bullet!!!!

 

[SoonerP226]

IIRC, you'll want 1:7 for that heavy of a bullet. As I understand it, 1:9 is generally fast enough for most .223/5.56 projectiles, and the 1:7 only came about because the Army wanted to be able to use the M249's heavier boolits in the M16. I don't recall exactly where the line was, but I think 70+gr falls in the 1:7 camp.

 

[AMT7]

Heavier or longer bullet is sometimes the debate.
You go 1:7 and it can over spin the lighter ones and MoBoost has done that and watched the bullet get out of the barrel and down range in mid air watch it vaporize.

Do a trajectory calculation and see the drop vs distance on the bullets you plan to use.
Heavier bullets get pushed less by wind..

Thank you swampratt for that good info!

IIRC, you'll want 1:7 for that heavy of a bullet. As I understand it, 1:9 is generally fast enough for most .223/5.56 projectiles, and the 1:7 only came about because the Army wanted to be able to use the M249's heavier boolits in the M16. I don't recall exactly where the line was, but I think 70+gr falls in the 1:7 camp.

And suggestion on website calculators better at this specific issue with 223 5.56x45 than most?

I have these heavier rounds for hunting with 5 of us hunting JSE upper 1:7 twist 14.5" nitrided bbls. And one, (me) 1:9 PSA FN double hard chrome 14.5":

Federal Premium Gold Match 69gr
Same as above 77gr
Privi Partisan PPC match 75gr

 

[Huckelberry75]

All three of the rounds that you listed are stated to be match rounds, and typically advised against for hunting purposes. That being an age old debate, I will not open that can of worms. What ever you decide on to hunt with, put it in the right spot, but don't expect the bullets to perform like a proper hunting bullet. For pelt saving on coyotes, you would be fine, but I would personally not hunt medium to large game (deer) with them.