Fast rate of twist?

[Mike6158]

8.6 Blk has 1:3 twist. That should be the bestest bullet shooter ever right? Full disclosure. I built one with a 16" barrel but other than testing it into the dirt (backland clay) I have no idea how that thing is going to work. I'm waiting for my can to get out of jail. I'll break down and take it to the range one of these days, well before the Alpha Tango Foxtrot group gets done. Word is that jacketed bullets don't stay jacketed in the 8.6. I got that word AFTER I had started building it. I have a few thousand 300gr Sierra SMK's and I thought I was set up good. The people ahead of me are loading solid copper. Idk. I like the idea of a fragmenting 500,000 RPM bullet slicing into a hog but... as my son-in-law pointed out... he's been killing hogs with a .223 for 15 years and he figures to stick with it. I like trying new to me schtuff... The worst case is I'll have a .308 lower to play with.

 

[Shubey]

Bullet RPM is fps x 720 / twist rate. So at 3000 fps with a 8 twist you're looking at 270,000 rpm. This is where you can overtwist, let's take a 55 grain bullet out of a 22 creed. Let's say you push it 3800 fps so 3800 x 720 / 6.5 your over 420k. That's cooking, quite a few bullets won't hold together at that rpm.

This is why i,m thinking barnes X bullets. Solid copper rod. I,ll stick to 70to 80 grain bullets too. Thanks for math equation, very helpful!

 

[kfreeze]

Just to keep in mind a bullet spun faster also wobbles more just like an out of balance wheel on your car vibrating more as you go faster.
So just like every thing else there are trade offs. In general slower twist will be more accurate given they're sufficient twist to stabilize the bullet your using.

Exactly. Everyone jumps on a fad and forgets what has been known for years, then the next question of why aren't my bullets making it to the target comes up. There is no one thing best for all situations. And going with more twist isn't always the answer. That's why a lot of benchrest guys run so slow of twist barrels.

 

[kfreeze]

I think faster spin would have more shock transmitted to animals. My 2cents!

Faster spin makes bullets more explosive on impact.

 

[Shubey]

This is why i,m thinking barnes X bullets. Solid copper rod. I,ll stick to 70to 80 grain bullets too. Thanks for math equation, very helpful!

Where does 720 enter equation?

 

[Radman]

Exactly. Everyone jumps on a fad and forgets what has been known for years, then the next question of why aren't my bullets making it to the target comes up. There is no one thing best for all situations. And going with more twist isn't always the answer. That's why a lot of benchrest guys run so slow of twist barrels.

Words of wisdom...

 

[1mechanic]

720 comes from.
12 x 60 = 720, there are 12" in a foot and fps is measured in seconds, to get seconds to minutes you multiply by 60.

 

[Shubey]

720 comes from.
12 x 60 = 720, there are 12" in a foot and fps is measured in seconds, to get seconds to minutes you multiply by 60.

Ah so ... Grasshopper now understands !

720 comes from.
12 x 60 = 720, there are 12" in a foot and fps is measured in seconds, to get seconds to minutes you multiply by 60.

Vital ?: Is it then accepted, that 270K rotation is starting point where bullet explosion could occur ?

 

[1mechanic]

Ah so ... Grasshopper now understands !

Vital ?: Is it then accepted, that 270K rotation is starting point where bullet explosion could occur ?

That really depends on bullet construction light thin jacket bullets like those used in a 22 creedmoor will usually start having problems but mono's don't care.

 

[Doom2]

Ah so ... Grasshopper now understands !

Vital ?: Is it then accepted, that 270K rotation is starting point where bullet explosion could occur ?

Berger states that ~300K is point where disintegration begins. Nobody wants to quote an exact number as it depends on multiple factors that vary with bullet construction.

 

[1mechanic]

Years ago in the 90's I was pushing some 87 grain Speer varmint bullets out of a 264 win mag at about 3700 fps which was about 296,000 rpm the third bullet peppered the 100 yard target like a shotgun. I stopped shooting those.

 

[Shubey]

That really depends on bullet construction light thin jacket bullets like those used in a 22 creedmoor will usually start having problems but mono's don't care.

I, ve ordered 70 grain barnes X bullets. You know any powder candidates? I was thinking of ramshot big game?

 

[1mechanic]

I don't have or load for a 22 creedmoor, someone who does will be better to answer.

 

[GuntherRLII]

I remember many years ago on the Coffee Shop a guy named Steve Shelp said he and a friend both had rifles chambered in 6.5-300 Weatherby aka 6.5 Wright-Hoyer. Their barrels had different twist rates. The faster twist killed with more authority according to him. Can't remember what bullet or velocity or twist rate. Just that fact.