7mm PRC Shorter Barrel Twist Rate

brianortegojr

brianortegojr

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Trying to decide which twist rate for 7 PRC rifle build. Going 22" barrel (either Proof or Carbon 6), would 7.5 twist be better than the 8 twist and would there be enough retained velocity at 1000 yds to ethically take elk at that distance with shorter barrel and slightly faster twist?

-Brian
 
brianortegojr said:
Trying to decide which twist rate for 7 PRC rifle build. Going 22" barrel (either Proof or Carbon 6), would 7.5 twist be better than the 8 twist and would there be enough retained velocity at 1000 yds to ethically take elk at that distance with shorter barrel and slightly faster twist?

-Brian
Click to expand...
yes it will give you a better stability factor out of that lower velocity.!.
 
My first question would have to be is a 1000 yard shot ethical? Are you capable enough to take that shot? Especially with factory ammo, if you don't reload I would assume you also don't have the tools to measure consistent bullet speed, SD, and ES. I guess if you practice enough and can land consistent MOA groups at 1000 yards maybe.
 
Dmagna said:
My first question would have to be is a 1000 yard shot ethical? Are you capable enough to take that shot? Especially with factory ammo, if you don't reload I would assume you also don't have the tools to measure consistent bullet speed, SD, and ES. I guess if you practice enough and can land consistent MOA groups at 1000 yards maybe.
Click to expand...
With the right equipment and circumstances yes I think 1000 yds is ethical. Ability to take the shot varies shooter to shooter and I will honestly say that presently I cannot and would not take that shot! Farthest I've taken any animal to date is 685 yds. As far as reloading, no, I do not reload. I do have tools to measure speed/velocity. Just looking to ensure the gun I build/have built with the ammo chosen would be capable. I plan on making it to BC's school for a weekend of learning in the very near future so that on future hunts if I'm presented a long range opportunity I will know what I need to know to make the right decision. Thanks!
 
brianortegojr said:
Trying to decide which twist rate for 7 PRC rifle build. Going 22" barrel (either Proof or Carbon 6), would 7.5 twist be better than the 8 twist and would there be enough retained velocity at 1000 yds to ethically take elk at that distance with shorter barrel and slightly faster twist?

-Brian
Click to expand...
Hornady quotes 3000 fps from Precision Hunter 175 ELDX ammo in a 24". Worst case scenario you'll lose 40 fps per inch (probably less, but let's be conservative), and we'll knock another 20 off in case your ammo or barrel comes in slow. So call it 2900 fps

At 2900 fps, 50°, standard sea level, a 1:8 twist will give you a 1.91 stability according to Berger's stability calculator (high end of "Comfortable Stability"). The JBM stability calculator, which accounts for plastic tips, gives 3.08 stability.

IMO, there's no reason to go to a 1:7.5 twist for that bullet (or any other 0.284 bullet except maybe the heaviest monolithic offerings).

Regarding 1000 yard elk performance, that's a tall order, but not out of the question.

At 4000' elevation, standard pressure, 50°, 50% humidity and a 2950 fps launch, the ELDX will only be going 1866 fps, and have 1352 ftlbs at impact at 1000 yds. Will that kill an elk? Sure. It doesn't leave much room for error though...
 
Estimate your velocity (25-30fps per inch loss), take another 50fps off for just in case and put it into the berger stability calculator.
 

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