Barrel twist in relation to type of rifling

[crackerbacks]

i have been toying with the idea of building a 6 creedmoor and I like what I hear about the dracos barrels but they only produce the 6 creedmoor in a 1-9 twist and I want to shoot the 105 hybrids so I asked about a 1-8 custom barrel. Here is their response:

Hello Matt,
At this point we do not provide custom twist barrels. I understand that our barrel twist rates are a little confusing to say the least, however keep in mind that we are not using the traditional style rifling. We are using Caudle Rifing. Caudle Rifling is a state of the art polygonal hybrid style rifling that has interesting characteristics. Our twist rates are designed to be the optimal twist rate for that barrel system.
Nick

Does this sounds right? My understanding was bullet stability was a direct relation to the rpm's after the bullet leaves the barrel? Maybe I am wrong?

 

[padom]

Easy, have PVA, Keystone Accuracy, Compass Lake, etc spin you up exactly what you want...

 

[crackerbacks]

Easy, have PVA, Keystone Accuracy, Compass Lake, etc spin you up exactly what you want...

I know there are a bunch of different options, I was just wondering if there was any credence to their claim? Always trying to learn

 

[padom]

I've never heard that a certain rifling makes say a 9 twist equal to a 8 twist but I'm also not a gunsmith so I truly don't know. I was talking to Compass Lake yesterday about different types of rifling and their comment was some clean up easier than others..

 

[BurnOut]

Sounds like bullshit to me.

Just my $.02.

 

[biffj]

The key to stability is the spin rate of the bullet. If you have long bullets they need to spin faster to maintain stability. Heavier bullets for a particular caliber are normally longer so need more spin. It doesn't matter if they have a double overhanded quicklock dingleberry setup if the twist rate is too slow for the bullet. Nothing in the rifling is going to speed up the twist if their rate is 1-9 and you need 1-8 so it sounds like BS to me too.

Frank

 

[TitaniumBlue]

Usually the caudle style rifling allows the bullet to travel a bit faster due to it's decreased friction. It's not all about twist rate for a bullet, it's about RPMs. For example, an 8 twist barrel with a muzzle velocity of 3000 fps, spins the bullet at 270k rpm. A 9 twist barrel with a muzzle velocity of 3375 fps, will spin the bullet at the same rpm. So there is some validity to their case, however, the velocity gains in that type of rifling are usually not a full 10% increase.

 

[Forgetful Coyote]

The "system" itself is a sham IMO.. I could go on and on but Ill just leave it at that.

 

[sandwarrior]

The 1-9" Caudle rifling may/may not stabilize a 105 Hybrid. But, why take the chance? Get the 1-8" twist and KNOW you are going to stabilize that bullet.

Of note here is that in the past we didn't have the concentricity in the bullets that we have today. That was why barrel makers were only making as tight of a twist as we needed. No matter what though, when we got to the heavies for each caliber, we had to twist barrels tighter.

Going​​ back to standard length/style bullets in those tight twists, is when we found the newer bullets with high tolerances wouldn't over stabilize.

 

[Yondering]

I know there are a bunch of different options, I was just wondering if there was any credence to their claim? Always trying to learn

I think they're feeding you a line of bs that's based on what they currently sell, not what's ideal. If they sold a different twist rate they'd tell you that was best.

For direct comparison, Black Hole Weaponry uses the same type of rifling and does offer 6mm 1:8 twist. I've got one in 243 LBC (6mm AR, 6mm Grendel, whatever you want to call it) in 1:8 that shoots great. I don't see any reason to go with 1:9 unless it's a cartridge like 6x6.8 that won't use the heavy bullets anyway.

As to the velocity difference - it's mostly theoretical. In my experience there's as much or more velocity difference just between different barrels than between different rifling types. Not to mention variations in powder lots, bullets, etc. My 24" polygonal 243 LBC barrel mentioned above runs ~100 fps slower than another guy's 22" from the same manufacturer with the same load; just the way it is sometimes, so you can't count on a polygonal always being faster.