Twist rates why choose one over another

J

JRB

Guest
Just seeing what makes one twist 'a better option' than another, with a PPC you have 13, 14 or 15 for 68's,
So shooting 68's, how and on what grounds do you decide?
I have heard for paper that the slower the twist the better for a specific weight? any truth?

Also for varmint rifles, it has been said that a fast twist will give better energy on your target.
what are the pros and cons of twist for both target and hunting purposes?
Does twist have any effect on throat wear, of is that mostly powder burn?

Jim
 
Too fast better than too slow

I believe Berger is now recommending a 13 inch twist for 68 grain 6MM bullets now. I have also heard it speculated, that since twist rates are not precise, perhaps some so-called "Hummer" barrels are just a bit faster twist than advertised. I have a 13.5 inch twist Hart on my 6 PPC and am quite impressed with it.

You will for sure notice a "too slow" twist a lot more than "too fast" unless you are talking fragile varmint bullets and high speeds. Then you may just see a puff of blue smoke and nothing on the target.
 
The 15 twist will work with 62 grain bullets on a .750 jacket, but it would be unreliable with a bullet on an .825 jacket. The 14 twist has been the standard for years, but slightly faster is gaining popularity lately.
 
For years it was the norm for 6PPC shooters to use a 14 twist.
In 1980 I was at the IBS Nationals in Syracuse NY and met Jerry Hart. I managed to buy from him a HV barrel with a 12 twist. Man, that barrel was a ripper. I shot everything in it from 62 to 70 grain bullets and it just devoured them all and won me a heap of matches. I also procured a 12 twist Shilen rail gun barrel and that was the same. Didn't seem to matter what bullet I put into it - it just shot beautifully.

So now we come to the later years and I have had mainly Bartlien and Krieger barrels in 13.5, 13.75, and 14 twists plus a few gain twists thrown in.
The only one that has given me any trouble was a 14.25 to 15 twist, that did not perform as well in colder weather which for us is anything under about 13 deg C.
Above that it is OK.

If I am buying barrels now I tend to stick with 13.5 twist, and I use an Australian made 67gn BT bullet on an 825 jacket - that combination is reliable and wins matches.
 
twist rates why choose one over the other

I believe it best stability with the bullet weight you choose.
I go by the stability program on JB balistics some twists are better then others from what i see on the program.
 
Jim
Rifle Barrels have a twist to put a spiral rotation on a bullet for stability. Similar to a thrown football you try to put a nice spiral on a football , imagine taking a football and throwing it sideways say 40 yards it is not going to work very well. A bullet needs a spin on it to keep it stable as it passes through the air. It is desirable to keep the pointed end forward and have no wobble on its axis. Any given bullet on any given day at any given temperature, and air density, requires a certain amount of rotational spin for maximum stability which translates to accuracy at the target. Unfortunately over stabilizing is also detrimental to accuracy. So the idea is to put just the right amount of spin on the projectile and worst of all the optimum twist varies with temp and air density. This is why twist of a barrel is critical for peak accuracy on a barrel and a little change can make a big difference. Someone spoke earlier in this thread of a 12 twist barrel that was a real shooter with 60-70 gr bullets, I would call this an anomaly it should not have worked that well but really good barrels sometimes defy the norms. I am told when calculating best twist it is more about Jacket length than bullet weight.
i know nothing about calculating ideal twist rate Get Hold of Randy Robinette (the Expert Bullet Maker) http://bibullets.com he can help you make the decision.
Dick
 
vtmarmot said:
I believe Berger is now recommending a 13 inch twist for 68 grain 6MM bullets now. I have also heard it speculated, that since twist rates are not precise, perhaps some so-called "Hummer" barrels are just a bit faster twist than advertised. I have a 13.5 inch twist Hart on my 6 PPC and am quite impressed with it.

You will for sure notice a "too slow" twist a lot more than "too fast" unless you are talking fragile varmint bullets and high speeds. Then you may just see a puff of blue smoke and nothing on the target.
Click to expand...

Twist rates not being precise......this is common with a button rifled barrel. The button can slip and the result is either a not uniform twist or the twist could keep getting slower as it goes towards the muzzle. This happens usually when the button hits a hard spot or soft spot in the steel. You don't have this problem with a single point cut rifled barrel.

Later, Frank
Bartlein Barrels
 
I tend to error a little on the faster side when I do a twist calc. for a certain bullet and a given velocity. Other factors that come into play are velocities, temperatures, altitudes etc...A guy shooting in Denver at 5000' can usually get away with a slightly slower twist than a guy shooting closer to sea level but if that Denver guy shows up at a match that is closer to sea level etc...he can run into problems with his barrel stabilizing his bullets.

Back around 1999 one of the top bench shooters called me and he was starting to make his own bullets and they had the longer jacket for the 6ppc bullets. He said some days the gun shot like a million bucks and some days it shot just o.k. The barrels he was using at the time were 1-14 twist. So he sent me some bullets and I did a twist rate calc. and at his velocities with his bullets I was coming up with a min. twist needed of around 13.68 or 13.86 (cannot remember anymore which one exactly) and I told him if it were my gun I would go with at least a 1-13.5 or even a 1-13 wouldn't hurt. So we made him some more barrels in a 1-13.5 twist and it was either that year or the next year he cleaned house at the Nationals I believe it was. That's when the 13.5 twist barrels really took off.

I tell guys this.....if you shoot a lighter bullet (shorter jacket length) in a faster twist usually it doesn't hurt you accuracy wise. The key is to shooting good quality bullets and that the loaded ammo doesn't have a lot of run out. A poorer quality bullet or the ammo having a lot of loaded runout, the runout etc...will be amplified by the faster twist and that's what makes the groups worse. It's the bullet length that is more critical in determining twist rate needed and usually not the bullet weight. Yes usually the heavier the bullet gets the longer the bullet gets but not all the time.

Not a benchrest example but a good example none the less. Years ago when I started playing with a Colt AR15a2 factory rifle for shooting hi power rifle matches. The factory barrel was a 1-7 twist. For being a rack gun it shot pretty good. With handloads and 69gr. Sierra's it would shoot right around 3/4" groups at a 100 yards. One day at the range I ran out of my handloads so I figured I would shoot some ball ammo I had to practice off hand shooting. Out of the first 5 rounds 2 or 3 of bullets went thru the target sideways. Those 55gr. bullets would stabilize in a 1-14 twist barrel. Went home loaded more ammo with the 69gr. Sierra's. I also had some 52gr. Hornady match bullets. So I loaded those as well. Went back to the range. Started with the 69gr. Sierra's. The gun went right back to shooting 3/4" groups at a 100 yards. I then shot 5 rounds of the ball ammo. Sure enough one of the bullets went thru the target sideways. Then I shot 20 rounds of the Hornady 52gr. boat tail match bullets. Guess what. Those Hornady's averaged a 3/4" group at a 100 yards also. No key holing etc... the difference was the quality of the bullets/ammo vs. the 55gr. ball ammo.

Later, Frank
Bartlein Barrels
 
Never mind about twist rate! You need a barrel that will shoot bullets in a single hole with whatever you can find to shoot in it...

Such barrels are hard to find and don't have anything to do with the twist rates mentioned. Sure, you have to tell the man what twist rate you want but what you really should ask for is the better barrel. Of course nobody knows....which is why benchrest shooting is interesting and somewhat expensive.
___________________________

Went back and read the initial post.....nevermind and sorry I wrote this...
 
Last edited:
Wilbur said:
Never mind about twist rate! You need a barrel that will shoot bullets in a single hole with whatever you can find to shoot in it...

Such barrels are hard to find and don't have anything to do with the twist rates mentioned. Sure, you have to tell the man what twist rate you want but what you really should ask for is the better barrel. Of course nobody knows....which is why benchrest shooting is interesting and somewhat expensive.
___________________________

Went back and read the initial post.....nevermind and sorry I wrote this...
Click to expand...

Wilbur I don't agree a 100%.

What about the problems there has been with bullets in the last few years!? How can it always be the barrels fault when there is a problem with bullets out there? I'm not going to name the brand etc...as it is irrelevant.

Also how can just the barrel be blamed when the other big factor is the guy pulling the trigger and making mistakes! Not catching wind changes, jerking the trigger you name it!

I'll give you a excellent example! Several years ago we made a special run of barrels per X shooters request. I won't go into all the specifics of the barrels. So when we made them I randomly kept one for myself for my bench gun build (and don't say I cherry picked thru the barrels because I didn't!). So as my gun is getting put together by a well named smith and I had one of the top bench shooters in the country test it for me before I even got the gun! When the gun was tested (LV gun) he had some groups in the 0's and he said it would shoot low to flat .1's with no problem. He said if I lose a match with it, that it wouldn't be the guns fault. So in the mean time I don't have the gun yet; I go to the Cactus Classic. I ask a couple of the shooters there that got some of those special barrels and I asked them if they were shooting them? They said no. I said why? They said they shot great but don't shoot in the wind so they are shooting the barrels we normally make them. I said BS! Don't give me that crap they don't shoot in the wind! Subject dropped......for now! We fast forward to the SuperShoot that same year. I now have my new rifle in hand. Spent a whole day with those same two shooters (by the way we get along great) on a practice day we spent shooting and loading together. The first time we went to the line I let one of them shoot my gun first. He really liked it and said it was shooting awesome. I shot the gun the rest of the day. One time while on the line the other shooter said hey the gun and your are shooting great you should shoot the next upcoming match with them. I said really!? He said yep and he said that gun won't let me down. I said really again? I then asked him what he thought of the wind conditions? He said yep tricky etc....I then dropped the bomb. I said well that's one of those barrels you guys claim don't shoot in the wind! You could've heard a pin drop in the dirt!

So it's always the barrel makers fault?

Later, Frank
Bartlein Barrels
 
My barrel was a 1-13.75 twist just for reference.

Later, Frank
Bartlein Barrels
 
Faster twist for a varmint barrel

My two cents on the faster twist for a varmint barrel is that you have more RPMs.

When the bullet hits the varmint you have a more explosive effect.

I shoot 12 twist for lighter bullets and eight twist for heavier bullets

The eight twist definitely makes a spectacular difference on a Prairie dog
 
I do not think that it is an accident that Berger made their newest short range benchrest bullet (the Column)on a .790 jacket. I think that it was so that it would have a better chance of doing well with all of the 14 twist barrels out there. Going up to Frank's post, one fellow that reported a significant improvement with the 13.5, when combined with his longish OO BTs, is Lester Bruno, and since I know how well he has done over the years, I tend to pay attention when he passes something along.
 
twist rates why choose one over the other

I agree with frank believe me he's right on with his calculations
The JBM program also helps a lot. Stability and accuracy are one in the same.
 
Does a faster twist wear faster?

If i had the option of choosing a new varmint barrel, and i could choose between a 9 or 12 twist
would there be any noticeable wear difference? with the same load.

Jim
 
JRB said:
If i had the option of choosing a new varmint barrel, and i could choose between a 9 or 12 twist
would there be any noticeable wear difference? with the same load.

Jim
Click to expand...

No, its fire cracking (or bad cleaning practices) that cause people to retire barrels, not wear from bullets going down the barrel.
 
Fergus Bailey said:
No, its fire cracking (or bad cleaning practices) that cause people to retire barrels, not wear from bullets going down the barrel.
Click to expand...

So fire cracking is caused by heat,
can you curve the impact by polishing every 100 shots with JB?
or is it a natural cause with no way to prolong the eventual?
Jim
 
Twist rate

Twist rate which induces gyroscopic stability in the bullet is more related to bullet length not weight. This is easily proven with a long light bullet and this has been tired tunnel many times. You need a faster twist for longer bullets. If the twist is too slow it will wobble like a football as described before. Twist rate has some but little effect expansion, varmint rifles usually see a difference in performance from bullet design, varmint bullets are made to disrupt on impact not expand as a hunting bullet should. When I built my first VFS rifle I used what everyone else was for twist the differences in ±.5 or 1 twist rate is hard to determine a true advantage since barrels in general vary internally and some just shoot better than others no matter what you put down the tube. I have seen fragile varmint bullets come apart in less than 100yds in over spun, i.e. shot really fast in a tight twist. I'm sure I left some holes in this info. ;)
 
You must log in or register to reply here.
Back
Top