30 cal 1:7 twist

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Lucky1 posted this yesterday

Hi everyone!

Just starting to work with a 300BO with a 1 in 7 twist. This is waaay faster than any 30 I have worked with and could use some advice on bullet selection and range of speeds that are appropriate for this one. I know there are several people who have formulas for calculating these parameters and are much more knowledgeable in this. Supersonic is fine since I don't have a can but I'm not opposed to subsonic ones. I can come up with molds from 155 to 230 grains. So where to start?

Scott Ingle

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John Alexander posted this 21 hours ago

I know nothing about the 300 BO nor about shooting subsonic with rifles. I do know that the 10" twist in my Springfield stabilized 250 grain Barns bullets at 2,300 fps. Of course these were round nose bulets and short for the weight. 1 in 7 seems excessive for any useful 30 caliber bullet. My wild guess (with no evidence) is it was chosen because 1 in 7 is common in 5.56 ARs. Can't imagine what kind of 30 caliber bullet would need  1-7 --- but maybe for subsonic. I did have a shooter come to our range with a box of factory loaded 5.56 with 112 grain bullets. They didn't shoot well in his 1-14 twist bolt gun. I asked for a round and still have the 112g bullet. So maybe someone is making 300 grain 30 caliber bullets.

I wouldn't worry about having too much twist for full charge loads. 110 grain 30 caliber bullets often shoot well 10 twist 30-06, and 40 g Hornady shoot great in my 1 in 8"  223.

Sorry I couldn't offer anything to answer your questions.

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Idahocaster posted this 15 hours ago

Would 300BO have a faster twist rate because it has a lower velocity? Barrel twist rate times muscle velocity gives you a bullet rpm. To get a similar rpm with a slower bullet you would need a faster twist rate.

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delmarskid posted this 5 hours ago

All I know is what I have read about the blackout in 1-7. It appears that some have had good luck with a Lee boat tail mold at about 1100 fps and under using H-110.

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Lucky1 posted this 4 hours ago

I'm thinking you guys are right about the 1 in 7 and slow, heavy bullets. And there is basically a speed limit in the number of rpms that cast can handle. I do have that Lee mold from way back when and could never get it to work in a 1 in 10 twist so this may be the one to try again. Thanks

Scott Ingle

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Tom Acheson posted this 3 hours ago

Long ago there was a movement afoot that promoted fast twist with light bullets in the CBA unrestricted “Pistol” match gun category. This would have been in “pistols” of unlimited weight and barrel length.

The 30 cal. twist rate was in the 1:7 neighborhood and muzzle velocities exceeding 2500 fps.

But maybe that genre of activity faded away?

Tom

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Lucky1 posted this 3 hours ago

Tom- you got my attention with that kind of velocity. So I'll dive back in the old results to see what's there. I wouldn't have thought about Unltd Pistol so thanks for that clue. Powder coating starts to come to mind too.

Scott Ingle

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Ed Harris posted this 3 hours ago

314299 is accurate and stable subsonic in the traditional 1:10" twist. A twist of 1:7" is excessive for any normal use and would rapidly degrade accuracy with lighter bullets at high velocity. Would be interested whether Larry Gibson might have tested one of these barrels and could contribute hard data as opposed to my guesswork.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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Tom Acheson posted this 3 hours ago

True, 1:7 twist may be excessive. What I was relating was a concept or theory advanced by a few. The 30 cal. bullets being postulated were 100-110 grains.

When the tech info from the 2026 National Tournament are published, we might see some UNP (Unrestricted Pistol) equipment details that fit the parameters that I was relating….along with their results.

Tom

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John Alexander posted this 2 hours ago

Tom,

I'm afraid your memory has failed you. Just wait till you get old.  You are right about the light bullets but have the twist part backward.

HL Yarborough won the unresticted rifle class at the 2007 nationals shooting a UNP (before there was a class for UNP), He used a 108 grain bullet in a 30 BR with a 22" barrel with a 1 in 18" twist. muzzle velocity was listed at 2,750 fps.

Pat Iffland also used a similar approach, in the same match, shooting a 155 grain bullet at 2,650 fpa from a 23" barrel with a 1 in 17" twist  and shot competitively.

It looked like CBA shooting might look very different in the future, but that approach disappeared without a trace. UNP shooters. like some others, are now shooting heavy bullets and twists only a bit slower than 1 in 10". I don't know why the light bullet, slowt wist, high velocity approach was dropped after such a dramatic beginning. You might speculate that the light bullet at high velocity approach might still be the way to go for cast bullet progress.

John

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