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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Twist Rates and Velocity?
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<blockquote data-quote="longrangehunterII" data-source="post: 777662" data-attributes="member: 61185"><p>Hi Montana Rifleman,</p><p></p><p>The book Applied Ballistics for Long Range Shooting by Bryan Litz is highly recommended reading for understanding external ballistics at great distances, but not light reading material by anyones means. </p><p></p><p>If it were me, or someone asked my opinion about which twist rate would I choose, I'd go as fast as possible from the barrel maker for the caliber. 1:8"; 1:8.5" or 1:9" in any .264; .284; or .308 would work very well for long range work with any of the long high BC bullets, or even the lighter ones. (Read "The Future of Twist Rates" by Todd Hodnett) in this months Sniper by Shooting Times magazine. Todd explains that even with a 14" 1:8" twist barreled .308 shooting 168-grain .308 ammo was able to out shoot everyone else until they switched to 175-grain ammo to make hits that far.... so I think the higher BC bullets would work even better in these barrels at those distances due in part by the added gyroscopic stability achieved along with there high BC.</p><p></p><p>Most of this is noticed only when the distances are stretched, the high retained velocity of those heavier bullets translates into more ft./lbs. of energy on impact at those great distances. Which does help to stay within the needed energy levels (1,000-1,500 ft./lbs.) for a big game animal or a target as far as less bullet drop that would be experienced. </p><p></p><p>I have a 300 Jarrett, and wanted a 1:10" twist to use those heavy long bullets, but got a 1:12" instead because that's what Kenny uses in his 300 Jarrett. We had that debate (years ago) and I lost because he doesn't like the interior ballistics of a loaded round when the bullet is seated well below the neck. So he was doing a re-barrel job for me on a Hunter Benchrest Gun built by someone else in .308 Bear which had to have the ammo load through the magazine, and the bullets would have to be deeply seated to fit, and among other things still weigh 10 lbs. or less with the scope which it does. Kenny now does make such a rifle for hunting or target use with his 300 Jarrett, but it's a single shot gun, and wears a 1:10" twist barrel. </p><p></p><p>So the lead angles and throat length would need to be addressed with regards to OAL within a given bullet combination for the added benefit of optimum interior ballistics. Which can through a monkey wrench in the big picture depending on which bullets are used for any cartridge and whether or not if works through the magazine you are using.</p><p></p><p>Hope that helps, and please forgive me if I'm repeating something you already know? As much as I think I know a subject, I still like reading something that might help me better understand something. </p><p></p><p>Good luck and thanks</p></blockquote><p></p>
[QUOTE="longrangehunterII, post: 777662, member: 61185"] Hi Montana Rifleman, The book Applied Ballistics for Long Range Shooting by Bryan Litz is highly recommended reading for understanding external ballistics at great distances, but not light reading material by anyones means. If it were me, or someone asked my opinion about which twist rate would I choose, I'd go as fast as possible from the barrel maker for the caliber. 1:8"; 1:8.5" or 1:9" in any .264; .284; or .308 would work very well for long range work with any of the long high BC bullets, or even the lighter ones. (Read "The Future of Twist Rates" by Todd Hodnett) in this months Sniper by Shooting Times magazine. Todd explains that even with a 14" 1:8" twist barreled .308 shooting 168-grain .308 ammo was able to out shoot everyone else until they switched to 175-grain ammo to make hits that far.... so I think the higher BC bullets would work even better in these barrels at those distances due in part by the added gyroscopic stability achieved along with there high BC. Most of this is noticed only when the distances are stretched, the high retained velocity of those heavier bullets translates into more ft./lbs. of energy on impact at those great distances. Which does help to stay within the needed energy levels (1,000-1,500 ft./lbs.) for a big game animal or a target as far as less bullet drop that would be experienced. I have a 300 Jarrett, and wanted a 1:10" twist to use those heavy long bullets, but got a 1:12" instead because that's what Kenny uses in his 300 Jarrett. We had that debate (years ago) and I lost because he doesn't like the interior ballistics of a loaded round when the bullet is seated well below the neck. So he was doing a re-barrel job for me on a Hunter Benchrest Gun built by someone else in .308 Bear which had to have the ammo load through the magazine, and the bullets would have to be deeply seated to fit, and among other things still weigh 10 lbs. or less with the scope which it does. Kenny now does make such a rifle for hunting or target use with his 300 Jarrett, but it's a single shot gun, and wears a 1:10" twist barrel. So the lead angles and throat length would need to be addressed with regards to OAL within a given bullet combination for the added benefit of optimum interior ballistics. Which can through a monkey wrench in the big picture depending on which bullets are used for any cartridge and whether or not if works through the magazine you are using. Hope that helps, and please forgive me if I'm repeating something you already know? As much as I think I know a subject, I still like reading something that might help me better understand something. Good luck and thanks [/QUOTE]
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