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 6mm twist rate
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Mark
Average Member



USA
112 Posts

Posted - Apr 04 2017 :  23:39:56  Show Profile Send Mark a Private Message  Reply with Quote
Ok, been away from the forum for a while, but I am looking to build a 6mm undecided on cartridge will probably be between 6mm AI and 243 win since I all ready have dies and brass.
My question is this if you were going to shoot 95 and 100 grain bullets more than likely the 95 nbt, which twist would be the best 1-10 or 1-8, I know they will both work but of the 2 which would be better if any diff!! I have to make a decision lol

mark

Shastaboat
Advanced Member



USA
8899 Posts

Posted - Apr 04 2017 :  23:48:06  Show Profile Send Shastaboat a Private Message  Reply with Quote
1 in 10". You just don't need anything in a faster twist. The 6MMAI will out perform the .243 Win but brass is cheaper and easier to get in .243 Win. I built a 6mm Rem years ago and it would out perform the .243 win. The 6mm AI is even better but .243 Brass is cheaper. You can always make brass from .308Win or 7.62x51.
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Mark
Average Member



USA
112 Posts

Posted - Apr 05 2017 :  00:14:00  Show Profile Send Mark a Private Message  Reply with Quote
I've been leaning toward 1-10 but it seems the fad is the 1-8, but they are shooting the longer bullets, this will be a hunting rifle.

mark
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WonderMan4
Advanced Member

USA
2761 Posts

Posted - Apr 05 2017 :  01:08:04  Show Profile Send WonderMan4 a Private Message  Reply with Quote
That would be a fine hunting rifle with a 1:10.

If you think you will shoot a lot, you might want to consider something else as a 243 will be hard on the barrel. It is an excellent caliber.

Keep the barrel clean and it will do you good.
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Shastaboat
Advanced Member



USA
8899 Posts

Posted - Apr 05 2017 :  10:41:59  Show Profile Send Shastaboat a Private Message  Reply with Quote
Fashion and fads may change but a good shooting rifle doesn't.
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Zero333
Advanced Member



Canada
717 Posts

Posted - Apr 05 2017 :  20:20:48  Show Profile Send Zero333 a Private Message  Reply with Quote
Am I the only one that thinks the 8 twist is a better idea for longer bullets ???

I shoot everything from 55gr to 107 gr out of my current 8 twist 243win.... If you're worried about loosing velocity due to a faster twist you're in luck because it's been proven (by Brian Litz) that the velocity loss is too small to make a real world difference. His conclusion (for example) going from a 10" twist to a 9" twist you "might" loose 1.25 fps,

Over-spinning a bullet aids it's ballistic coefficient. Plenty top tier Palma shooters noticed their scores improved when they used a 10" or 11" twist barrel instead the usual 13" twist.

I shoot 130gr TTSX in a hunting 300winmag 10" twist barrel and that's the most accurate load in that gun. A 13" twist would suffice for the 130 ttsx but the 10" twist works very nicely for me.

Ran the #'s in Berger's twist rate calculator for the 95gr BallisticTip (1.115" long) at 3,050 fps. A 10" twist has a SG of 1.19,... 9" twist SG = 1.47,.... 8" twist SG = 1.86,... and optimal twist is 8.75",... according to the twist calc.
SG of 1.5 and higher is optimal,... SG between 1.1 and 1.4 is Marginal,... SG of 1.0 and under is insufficient to stabilize that bullet.

I gave you my opinion. Whatever you choose you have to live with.

Treat that trigger like it’s your first date, not like you’ve been married to it for 20 years.
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Shastaboat
Advanced Member



USA
8899 Posts

Posted - Apr 05 2017 :  23:46:45  Show Profile Send Shastaboat a Private Message  Reply with Quote
You don't need a 1 in 8" twist to shoot any commercially made .243 caliber bullet. Maybe if you were going to try shooting some 115+ gr bullets but then just buy a bigger caliber. The heaviest commercial .243 cal bullet I've seen is 100 gr and a 1 in 10" will handle it just fine. The fastest twist barrel I've worked with is a 6.5x55 Swede which I've seen it reported to be a 1 in 7.5" to 1 in 8". The fast twist was done to shoot heavy for caliber bullets. The military round was originally 160 gr and the fast twist was necessary to stabilize that bullet. The common weight for hunting now with a 6.5 caliber is 140 gr and generally will over penetrate and not expand. I routinely use 120 gr bullets in the 6.5x55 now and am very happy with their performance. One of my rifles sports a 1 in 10" and shoots as well with 120-140 gr bullets as the fast twist military version but at slightly lower pressure for the same loads.

Here is a good read on the .243 Win. which was originally designed in 1 in 10" twist to stabilize the heaviest .243 bullets.
https://en.wikipedia.org/wiki/.243_Winchester
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budlight
Advanced Member



USA
1611 Posts

Posted - Apr 16 2017 :  11:14:40  Show Profile Send budlight a Private Message  Reply with Quote
My 243 Remington 700 sps Varmintor came with a 26 inch 9 1/4 twist. Remmington really got it right with that twist rate. It works really well with 72 to 105 grain bullets. I would not go with 10 unless you want to use under 70 gr. The 8 twist is for specialized match grade VLD bullets up to 115 grain.

105's are SPBT and very available, but only a minor gain in BC

243 win is already a barrel burner. 6mm, 6mmAI 6mm-06 are even worse.

the key to speed is slow powder and a 26 inch or longer barrel. My target/hunting round uses superformance or R-26 powder and chronos right at 3200 fps with 100 grain nosler spbt
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