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> Precision long range hunting and shooting
> 7mm practical twist rate
7mm practical twist rate
@ 11:26 am (GMT) |
Tom ArundellHi, I know that the optimum twist rate for the practical has been emphatically put at 1/9 and ideally that is what I would like to get. I am just wondering what the verdict is on 8.5 twist. Please understand that I am not seeking for the faster twist this is purely a matter of availability (i can easily get an 8.5 but a 9 is proving harder to track down at the moment..)I know 8 is too fast, if an 8.5 is no good i will find a 9, I just wanted to ask in case! I have learned so much from this website and from all of Nathan's books and have been very excited to build a 7mm Practical! I have been saving for a long time for this rifle build and want to do it right! thank you to anyone with input that can help me out! and a huge thanks to Nathan for all his work! |
Replies
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@ 11:39 am (GMT) |
Tom ArundellRe: 7mm practical twist rateI should mention that I am planning to shoot 180gr ELD-Ms in this rifle.thanks again! |
@ 10:45 am (GMT) |
Nathan FosterRe: 7mm practical twist rateHi Tom, 8.5 is still a bit iffy, sometimes unforgiving. Its the little things that will catch you out, a bore finished slightly too high (as is the trend now) may for example produce pressure spikes. The ELD-M is also a max tolerance projectile (diameter).9 is very good, but a canted four groove 9 twist is optimal. That's the trouble, easy to miss seemingly minor variables. an 8.5 twist bore with 6 grooves at right angles is less forgiving than a 9 twist 6 groove, a 9 twist 4 groove canted - or for that matter, a simple rechamber on a Rem M700 7mm Rem Mag factory rifle and barrel with 9.5 twist and 6 grooves. I should also mention (for Rem Mag users) that a stock Sendero 7mm Rem Mag (9.5) can put the 180gr ELD-M into one hole at 100 yards, sweet spot normally about 2860fps. The Rem Mag can also shoot 190gr target bullets quite well, even if this twist is less than optimal for the heaviest of bullets. There is of course a chance that the 7mm pills will keep getting heavier. The 190gr A-Tip is an example of this (well suited to 8.5 twist). But it helps to keep things in perspective. You may not want a bullet heavier than 180 grains (or more costly than the 180gr ELD-M). You may want to use other bullets in your rifle for versatility, the Partition, the ELD-X and so forth. These are questions I cannot answer for you. |
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@ 11:23 am (GMT) |
Tom ArundellRe: 7mm practical twist rateThanks for that information Nathan, I will make sure I get a 9 twist and preferably a canted 4 groove!Out of interest have you been able to test any of the A-tip projectiles yet? Sorry if I have missed this somewhere else that you have spoken about them |
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@ 01:41 pm (GMT) |
Nathan FosterRe: 7mm practical twist rateHi Tom, the A-Tip is actually very old, its the original A-MAX design, before Hornady moved to plastic tips. Nothing all that new here. The lone survivor of the original line was the .510 caliber 750gr A-MAX. The Ali tipped A-MAX was / is a good game hunting bullet.I have not yet had time to study the latest A-Tip version. There are some factors which I want to isolate and study very closely over time. |
@ 07:33 am (GMT) |
Jake CareyRe: 7mm practical twist rateIs there a velocity at which the 180 ELDM begins to behave safely in an 8 twist instead of a 9? Berger's calculator thinks it's fine in 1:9 down to 2500 at my altitude, but I keep thinking of trying Shilen's canted 4 land, which is only available in 1:8. I don't know of another maker doing that in my price range right now. Would the geometry make the twist gentle enough for the 180 at around 2700 fps? I'm assuming it's still an unnecessary idea, but one wonders. |
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