barrel twist?

1423 Views 5 Replies 5 Participants Last post by Jeremy, Mar 14, 2006

only mortal

Discussion Starter · Mar 13, 2006

alright, I'm cashing in on my n00b question. What is the diff between a barrel with a slow twist and a fast twist? and how do you determine the need for one over another? was reading an article and it started giving out the ratio of twist in a barrel and I started feeling drowsy...

have no idea whats goin on :?

thanks in advance

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Ducman

· #2 · Mar 13, 2006

a 1:9 twist is one revolution per 9 inches, 1:12 is the one per 12 inches
1:9 is a faster rate than 1:12

Heavier/ longer bullets need to be spun faster than lighter bullets to be stabilized while in flight

but if you spin a light bullet to fast, it can come apart and if you shoot a heavy bullet with to much velocity for the twist rate than it can't grip the rifling

you match the twist to the bullet weight and velocity you want to shoot.

The better you match the rate to the rond the better accuracy you will get.
get it wrong and accuracy will become very poor at long distances
But there is room in the #'s
for .308 you can shoot 155, 168 and 175 grain all out of the same twist rate, but the accuracy will fall off as the distance increases, about 600 yards for 168gr and 800 yards for 175gr, out a 20" inch barrel, increase the barrel length will increase the velocity keeping the bullet stabilized longer, so 24" barrel may get you to 1000yards with 175gr

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brucelee

· #3 · Mar 13, 2006

Ducman said:
a 1:9 twist is one revolution per 9 inches, 1:12 is the one per 12 inches
1:9 is a faster rate than 1:12

Heavier/ longer bullets need to be spun faster than lighter bullets to be stabilized while in flight

but if you spin a light bullet to fast, it can come apart and if you shoot a heavy bullet with to much velocity for the twist rate than it can't grip the rifling

you match the twist to the bullet weight and velocity you want to shoot.

Well said.

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Jeremy

· #4 · Mar 13, 2006

Let me add that it's noticable at closer ranges also, not just long range.

If you have a totally wrong twist rate for the load you're shooting, It will be very noticable at 100yds and even closer. You're shots will be scattered all over the place,sometimes making an odd shaped hole and in very bad cases they will keyhole the target.

If your shooting an off the shelf gun with factory ammo you will very very very rarely ever encounter a problem with the barrel's twist rate. It's mostly in handloading and making hotloads and special heavy for caliber bullet loads where twist rate becomes an issue.

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vacca rabite

· #5 · Mar 13, 2006

Yeah, you can tell somehting is wrong even at 100 yards.

Also, bullet comp should be suited to the twist rate as well. For instance:
My 45-70 I was shooting a stout load of 450gr lead round nose bullets. 24 inch barel with a pretty quick twist. But the lead was too soft, and those heavy bullets did _NOT_ like the quick twist. Even at 100 yards, with a bench rest, the rifle would not calm down - 7 - 10 inch groups were not uncommon. I got very frusterated, till a freind suggested that the twist might be too fast, try a lighter bullet.

So, I went down to 350, lead flat nose. Suddenly, I was ringing beer kegs at 400+ yards off hand.

Zach

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Jeremy

· #6 · Mar 14, 2006

I had that problem with my .300 but i had to much velocity for the bullet size, I guess 3300fps is faster than a 200grn ball is meant to go lol .I had to switch to a 1:14 to 1:9 gain twist rifled barrel to get the bullets to stabalize.

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