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 16" 1in 7 twist vs. 20" 1 in 9 twist (using heavy bullits)
whywork40  [Team Member]
5/20/2003 10:07:51 PM
Hello, would a 16" rifle with a 1 in 7 twist shoot the 69,72,75 and 77 grain bullets better than a 20" 1 in 9 twist? Thanks
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Mike_L  [Member]
5/21/2003 4:59:48 PM
A 20" 1/9 may or may not work with the 75 & 77gr. It does in some people's guns, it doesn't in others (like mine). It'll work fine with the 69gr and probably with the 73gr. The 16" 1/7 will work fine with all of them.
notack  [Team Member]
5/21/2003 5:36:50 PM
[url]ammo-oracle.com[/url]
Jetlag  [Team Member]
5/21/2003 6:10:27 PM
If your just looking to throw em all downrange get the 1/7, but if you want accuracy there are better twists out there.
DevL  [Member]
5/21/2003 6:48:03 PM
[quote]Originally Posted By Jetlag: If your just looking to throw em all downrange get the 1/7, but if you want accuracy there are better twists out there.[/quote] Please explain this comment to all the people getting sub .5 MOA from those rounds and using that twist please.
whywork40  [Team Member]
5/21/2003 7:10:59 PM
So, that ammo page says that a 1:9 twist will stabalize a 40-75 grain bullet with a lead core. But if the bullet is steel it is longer for the same weight and a 62 grain steel bullet is as long as a 75 grain lead core.
DevL  [Member]
5/21/2003 9:01:23 PM
Its more complicated than that for example the 77 grain ammo is shorter than the 75 grain ammo due to the more taperd shape of the 75 grain ammo and there are air pockets at the tips of those bullets too. A 1/7 twist 16" barrel will stabilize a 75 grain bullet better than a 20" 1/9 twist. I think that answers your question. The 1/9 stabilizing the 75 grain round is a lie perpetuated by Bushmaster so they wont have to switch to the 1/7 twist. It will stabilize a 69 grain bullet in every barrel lenght though.
Jetlag  [Team Member]
5/21/2003 10:11:35 PM
[quote]Originally Posted By DevL: [quote]Originally Posted By Jetlag: If your just looking to throw em all downrange get the 1/7, but if you want accuracy there are better twists out there.[/quote] Please explain this comment to all the people getting sub .5 MOA from those rounds and using that twist please.[/quote] 1/7 may work fine but it spins the bullets faster than necessary, which is not a good thing.
Yojimbo  [Member]
5/21/2003 11:17:31 PM
[quote]Originally Posted By Jetlag: 1/7 may work fine but it spins the bullets faster than necessary, which is not a good thing.[/quote] Not trying to be a smart ass, but why is it not a good thing if the 1/7 is getting .5 MOA? What difference does it matter how fast it's spinning make if it's producing those kinds of results?
Jetlag  [Team Member]
5/22/2003 11:12:01 AM
I certainly would not encourage someone who is achieving such accuracy to dump their setup, but when someone is starting fresh why not pick a twist closer to what is optimal? A bullet spun too fast is less accurate than a bullet spun just right, that's just the way it is.
Yojimbo  [Member]
5/22/2003 2:19:44 PM
I guess it boils down to whatever you find as accepatble combat accuracy. To me a 1/7 shooting .5 MOA is probably even 4 to 6 times better than what I feel would be acceptable in a combat carbine. So I would say it more than meets the requirements. I really don't believe a .25 MOA accuracy difference or whatever will be missed in a combat situation.
DevL  [Member]
5/22/2003 2:50:03 PM
So jetlag what twist would you suggest for 75 grain ammo if not a 1/7?
Jetlag  [Team Member]
5/22/2003 3:39:00 PM
1/8. Looking back at what I originally said "if you want accuracy", that seems to imply you would get inaccuracy out of a 1/7, and that was definitely not my intention. The question was pretty vague. To come up with a concrete answer a lot questions still need to be answered. What rifle? What chambering? Factory ammo or hand loads? Velocity? At what distance? Air density? Seriously. Some are implied, some are not. We can take educated guesses and give a general answer, as I did. But I simply did not want to leave it at that, so I mentioned there are better twists for that range of bullets, and there are. There are no simple answers and I didn't want it to appear as though there were.
FMJ  [Member]
5/22/2003 3:55:11 PM
can a 1/8 do what the 1/7 can?
DevL  [Member]
5/22/2003 4:11:57 PM
I thik jetlag was implying a 1/7 twist would over stabilize the bullet at long ranges. Then again the shorter the barrel the lower the velocities and the slower the RPMs so a .223 pressure loaded 75 grain round from a 16" barrel would have less RPMs and be less over stabilized than a 20" barreled 1/7 twist rifle firing 5.56 pressure ammo. The 1/8 twist is great for longer barrels but I dont think he will be giving up anything using the 16" barrel and 1/7 twist. I am pretty sure "if your just looking to throw em all downrange get a 1/7" implies a lack of accuracy though. [;)]
Jetlag  [Team Member]
5/22/2003 4:16:25 PM
[quote]Originally Posted By FMJ: can a 1/8 do what the 1/7 can?[/quote] In regards to...? M856 and 100+gr bullets? They are better off used through a 1/7.
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