Hornady 147 gr. bullets and twist rate?

[Litehiker]

I just got some Hornady ELD-X- 147 gr. factory ammo and a box of the same bullets.

*The bullet box sez they recommend a 1: 8.5 " twist rate. Both my RPR and RAP rifles have a !:8 twist. Is another 4 grains (above the *Hornady 143 gr. ELD-X really going to shoot worse? I'll have to test and report back. Maybe I just bought 100 bullets that my rifles won't like. We'll see.

Anyone with experience using this round?

Eric B.

[rardoin]

Eric, running  faster twist (8tw) than the recommended 8.5 won't be a problem.  Running a slower twist would be an issue.

[Danbonzo]

I just got some Hornady ELD-X- 147 gr. factory ammo and a box of the same bullets.

*The bullet box sez they recommend a 1: 8.5 " twist rate. Both my RPR and RAP rifles have a !:8 twist. Is another 4 grains (above the *Hornady 143 gr. ELD-X really going to shoot worse? I'll have to test and report back. Maybe I just bought 100 bullets that my rifles won't like. We'll see.

Anyone with experience using this round?

Eric B.

A 1:8 will stabilize those projectiles even more effectively than a slower 1:8.5. which will help you maintain BC downrange easier than using mv to do said same.
Rob is using the 147's and reporting good results.

[jvw2008]

Air density plays a significant role in the actual BC of a bullet. The higher the altitude, and thus the lower the air density, the less twist rate is required to stabilize a bullet.  So at a mile high the 147 gr ELD would stabilize nicely with a 1:9 twist. Hornady is following convention of values determined at sea level when they recommend a 1:8.5 twist.

[Litehiker]

Thanks guys.

JVW, It's heating up here in 'Vegas so that means our 2,200 ft. altitude at my range will be more like 5,000 ft. in 100+ temps. I guess may 1:8 twist will be OK.

I didn't know thinner air (lower altitude density) meant a slower twist was not affected as much with a bullet heavier than the range of weights for which the twist for a certain caliber was designed.
Maybe I can shoot some 69 gr. 5.56 ammo in my 1:9 twist Steyr AUG bullpup when it heats up this summer. Worth a try. 1:9 twist has been tested to have the widest accurate range of 5.56 bullet weights of any twist rate. We'll see.

Eric B.

[Denver Steve]

How fast your pushing the bullet plays a huge role as well. In a 1-8" twist at 2700 fps the bullet is spinning at 240,000 rpm. Knock that bullet down to 2100 fps say grendel velocity same twist is only 189,000 rpm. Huge difference thats the same rpm as shooting 1-10.5 twist at 2700 fps!!! So not near as stable. Thats why guys lobbing around heavy subsonic bullets in a blackout use 1-7" twist instead of the normal 1-10", gotta compensate for the velocity. Bullet rpm is "velocity x 720 / twist rate."

[Rob01]

You are fine with the 8 twist. I was shooting the 147 in an 8 twist the other day in 55 degree weather at 400 feet ASL and had no issues out to 1020 yards. They stabilize fine in an 8 twist.

Also the 147 is an ELD-M and not an ELD-X.

[stormin_moorman]

How fast your pushing the bullet plays a huge role as well. In a 1-8" twist at 2700 fps the bullet is spinning at 240,000 rpm. Knock that bullet down to 2100 fps say grendel velocity same twist is only 189,000 rpm. Huge difference thats the same rpm as shooting 1-10.5 twist at 2700 fps!!! So not near as stable. Thats why guys lobbing around heavy subsonic bullets in a blackout use 1-7" twist instead of the normal 1-10", gotta compensate for the velocity. Bullet rpm is "velocity x 720 / twist rate."

Denver Steve, i thought that the velocity won't change the RPM's if the twist rate is consistent.  I mean an 8 twist is an 8 twist no matter how fast you're going.  The projectile may spin more per linear foot of travel because its covering more ground, but in order to spin it faster you need a faster twist barrel.  I could be wrong though, just my thoughts on the subject.

[Aussie65]

Some info on it.
http://bulletin.accurateshooter.com/2008/06/calculating-bullet-rpm-spin-rates-and-stability/

[Denver Steve]

Rpm is directly related to velocity. For example if your barrel is 2' long(24") with a 1-12" twist and the bullet goes through at one foot per second. Your bullet will spin at 60rpm(one rotation per second) making two full turns in the barrel in two seconds then exit. If you double the speed to two feet per second. The rpm also doubles to 120rpm the bullet is still only making two full turns in the barrel but taking only one second to exit now. Its like pushing a patch down the barrel. It spins nice and slow but if you speed up so does the speed the patch turns in the barrel. Are patches arent going through at 250,000rpm 

[stormin_moorman]

I think i was talking apples and you were talking oranges.  I was saying that if you have a 1:12 twist, it always makes one revolution per linear foot no matter how fast you push the bullet.  I got discombobulated on the whole "RPM" part.  But, yes you're exactly right on that. 

[stormin_moorman]

Anyway...blah, blah, blah....math, math, math

Here's the easy button

http://www.bergerbullets.com/twist-rate-calculator/

[Rob01]

Here's an easier button. They work in an 8 twist. Lol