Correct Barrel Twist-6mm 115DTAC or 107SMK

2Shots

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I keep running my bullet stability software and it tells me to run a 7 twist on these bullets in the 2800 to 2950 fps range for my .243 build. I can find lots of 8.5, 8, 7.5 twist barrels but no 7 twist. What are you 6mm guys running? Seems awful fast to me.
 

19Scout77

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Re: Correct Barrel Twist-6mm 115DTAC or 107SMK

Too fast a twist and too slow velocity. 26" 7.5 twist 115 dtacs should be right around 3k without issue.
 

19Scout77

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Re: Correct Barrel Twist-6mm 115DTAC or 107SMK

42 grains of h4350, br2 primers, lapua brass, HBN coated Dtacs, mag length=no pressure signs...but I would not go any heavier with the powder.
 

MTETM

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Re: Correct Barrel Twist-6mm 115DTAC or 107SMK

No Problems with 7.5 or 7.75 with DTACS.
 

2Shots

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Re: Correct Barrel Twist-6mm 115DTAC or 107SMK

I have a box of both the coated and uncoated DTAC bullets, should I be aware of any difference when I load?
 

knockemdown

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Re: Correct Barrel Twist-6mm 115DTAC or 107SMK

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 19Scout77</div><div class="ubbcode-body">Too fast a twist and too slow velocity. 26" 7.5 twist 115 dtacs should be right around 3k without issue. </div></div>

This.

I'm running molyed 115DTACs @ 3070fps easy from a 26" Rock 5R, 1:7.5" twist. GAP Match chamber...
 

19Scout77

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Re: Correct Barrel Twist-6mm 115DTAC or 107SMK

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 2shots</div><div class="ubbcode-body">I have a box of both the coated and uncoated DTAC bullets, should I be aware of any difference when I load? </div></div>

It has been my experience that uncoated actually run a little faster with the same load and no more pressure. The only reason I use the coated is that a buddy gave me a couple thousand when I built my .243. YMMV.
 

2Shots

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Re: Correct Barrel Twist-6mm 115DTAC or 107SMK

I thought the whole reason for running the moly is less friction so more velocity. Or maybe since its lower friction it's less pressure, so less velocity. I'm confused.
 

buffybuster

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Re: Correct Barrel Twist-6mm 115DTAC or 107SMK

I've shot 115's with an 8-twist with no issues. But theoretically in cold temperatures near sealevel, the 8-twist could become marginal. A 7.75-twist will put you in the safe zone under all conditions.