Potential downsides to fast twist barrel?

[Wilderness Blacktail]

So I have a rifle I'm thinking about rebarreling. It has to be fast to spin the longer monos I need to shoot.

Got me thinking, so a fast twist is needed to stabilize long bullets but it can over stabilize shorter cup n core bullets enough to create blow up issues. Of course some shorter bullets wont shoot as well.

Aside from this are there any other downsides? BC, barrel wear, terminal effects??

 

[sedancowboy]

You have to twist enough to fully stabilize the heaviest bullet you intend to shoot.
Regardless of what it does on the light bullet end. You can't over stabilize a bullet, you can spin the jacket off some lightly constructed bullets. With Monos that is not a problem. According to Brian Litz you will only loose about 5fps per inch of twist you increase.
Hope that helps
Henry

 

[Deleted member 103481]

I can't shoot well enough to tell yet, but I've seen some long range benchrest and f class people preferring to be on the slow side(well slow vs obviously fast). I know there was a thread on AS talking about the increased BC of spinning a 215 faster vs the inherent precision of spinning it slower (but enough) and which was the better option.

this is really talking about the edge of precision though, and I know this isn't a Br sight. Just worth noting when considering all downsides.

 

[ducky]

but it can over stabilize shorter cup n core bullets enough to create blow up issues.

As long as they don't come apart leaving the barrel, I'll only shoot them at things I want them to blow up on!

Whatcha buildin?

 

[Wilderness Blacktail]

Thanks gents. The answers seem pretty much in line with what I was thinkin so that's good.

I have a Wby Vanguard in 6.5-300, B&C stock, w/ a Timney that's gunna need a barrel in another 4-500 rounds or so I read. Not settled on a caliber yet but lookin at a 2.5" mag 25-28 cals. Also considering short mags but Im not sure bout losing a round of capacity.
The big case is cool and fun but man I hate watching 88 grains of powder go thru that hopper! Haha
I'm in northern California so lookin at the sleeker monos for huntin and cup n cores for practice... if I end up goin with a $1.00 + each huntin bullet.

 

[lancetkenyon]

I did load work up for a 6SST. 28" 1:7" 4 groove.
Pushed an 85gr V-max @ 3650+ and they vaporized out of the barrel @ 376,000RPM. More than that thin jacket could handle.
But it loved the 101 Hammer and 110 SMKs!

 

[MagMan]

I try to stay under 320,000. Lots of people will say 300,000 is the threshold for common cup/core bullets. I've shot plenty over that but when you have a few hundred rounds down the pipe all the sudden "poof".

MV X 720/Twist Rate = RPM

 

[jrock]

I've had this thought creep back into my mind. I built a 338 NM for the 300 grain bullets with a 9.35 twist and have recently tried the 265 grain ABLRs. They don't appear to show any really accuracy potential even though I can key hole or even 'Davy Crockett one hole' with the 300s. Its like that nagging feeling I left the coffee pot on even though I don't drink coffee.

 

[azsugarbear]

I have found that a fast twist barrel by itself is not a factor in bullet degradation, but rather a combination of fast twist coupled with high velocity. I have personally witnessed cup and core bullets disintegrating after leaving the barrel in my 270 Allen Magnum. In testing a new bullet I thought I was missing the target, so I kept moving it closer to see where the bullet was hitting. Finally, at about 30 yds. I saw a target that looked like it had been hit by a shotgun blast. The bullets were coming apart after leaving the barrel, spewing pieces of brass and hot lead down range.

 

[IHFarmer07]

There is another video on this that he made but I have to search more.

 

[Jon Bischof]

This is both fascinating and terrifying at the same time...sorta like when you drink too much coffee and you are filled with equal parts joy and rage.

I tried Berger 156 grain in my new Sauer 6.5 CM, thinking that might be a great bullet for the farther shots I may take on deer. First three all keyholed the target, impacting sideways. Anyway, the Twist on this rifle is 1:8.66" Yeah, that is the first time I've see that too. After reading this thread, it makes a lot more sense to me now. Sauer didn't engineer this sporter weight rifle to be a long range tool. After shooting every bullet weight from 125 to 156, it seems they chose this Twist Rate to do best with 129-140 grain bullets. I does OK with 142 Accubond LR and 143 ELD-X, but it is fantastic with 129-140 grain bullets. So, I guess that's what I will use for hunting this Fall. But I have not had any truly long range shot opportunities yet where I hunt anyway, so my shots will be under 400, most likely.

I noticed that their 6.5 PRC rifle has a 1:8" twist, so they are thinking folks will want to shoot longer heavier bullets in it.

 

[J E Custom]

So I have a rifle I'm thinking about rebarreling. It has to be fast to spin the longer monos I need to shoot.

Got me thinking, so a fast twist is needed to stabilize long bullets but it can over stabilize shorter cup n core bullets enough to create blow up issues. Of course some shorter bullets wont shoot as well.

Aside from this are there any other downsides? BC, barrel wear, terminal effects??

In my opinion, picking a twist rate that will work within a range of bullets you might want to use. To fast eliminates light fast bullets and to slow eliminates heavy slow bullets. I don't recommend choosing a twist rate for one bullet, because if the barrel doesn't like it you are doomed to poor accuracy. if you chose a twist rate for a range of bullet types and weights you build in some flexibility and can use several different bullets with good accuracy.

The reason many precision shooters chose a slower twist rate is that it engraves the bullet easier and does a better job consistently.

Fast twist are tough on many bullets and over rotation can always be a problem if velocities are high. Besides over rotating the jacket and spinning it off, at some point the balance of the bullet comes into play and can lower performance.

J E CUSTOM

 

[Craig Miller]

J E,

What's your opinion of gain twist rifling?

 

[J E Custom]

J E,

What's your opinion of gain twist rifling?

This is something I am still undecided about the advantages and disadvantages.

In theory the gain twist appears to have all the advantages, but in actual use that doesn't appear to prove out.

I have had several and still do own one, and being anal I try to look at fired bullets to inspect the engraving on the bullet and find that the best, most uniform engraving Is with slower twist rates and the worst looking is the gain twist. The fast twist rates are in between in quality and uniformity.

As far as the most accurate, the standard rifling, proper grove count and twist rate has been the best for me.

Just my experience with different twist designs.

J E CUSTOM