Home Forums Hunting & Shooting Hunting Rifles Barrel twist: factory spec vs actual?

Got a Winchester Model 70 Weather Extreme in 264 Win Mag made in 2013.

Factory spec says barrel twist is 1:9, i.e. 1 rotation in 9"

I measure the barrel twist at between 1:8.25 and 1:8.5. I am happy with the slightly faster twist rate, but:

How close should factory spec barrel twist be to the actual measured barrel twist? Seems to me that the factory should be able to hit the specified twist spot on . . . ?

shinbone, I have noticed the same thing. And, as in your case, your measurement is probably accurate if you used the "tight patch" method, because the patch can rotate slower than the twist, but not faster. RJ

I am also interested in this. I do not have answers, but I have a gun that according to specs should have a 14 twist, but my gunsmith came up with a 15 inch twist...

This issue has always been around. Tolerances. Some factory barrels are on the fast side of the tolerance and some are on the slow side. Their main concern is that it stabilizes the projectiles that they specify.

Not long ago I had three newer Remington 700s chambered in 243 that measured 9.125"(spec), 9.25", & 9.5". IMO there are no guarantees with factory stuff, or at least with Remington's barrels.

My next question is that if the factory can't control the twist rate well enough to hit their own design specifications, how do we know the twist rate is constant through a single barrel? In other words, if the factory can't control the twist rate from barrel to barrel, how could the factory control it within a single barrel? I am thinking the same mechanism that controls twist from barrel-to-barrel is the same mechanism that controls it within a barrel. And, seems like a randomly changing twist rate within a barrel would create vibrations and hurt accuracy.

Again the answer is partially tolerances. Factory barrels are pretty good, some are even fantastic. When not satisfied with a factory offering, a premium, higher priced aftermarket barrel is what you want and what they were made for. I do not know specifically about rates of twist variations in the same bore or if it is a measureable detriment to accuracy. They do make "gain twist" barrels that progressively speed up the rate of twist and their accuracy doesn't suffer. Another thing to consider is bedding. The factories have been using a pressure point out on the forend for years because most barrels are helped and if not helped are not overly degraded by it. Free floating on the other hand helps some rifles immensely and hurts some others. It is the law of averages and tolerances. Read that as cost effective.

Of course manufacturing tolerances are always present, but the details aren't lining up in this instance.

We are talking a Winchester factory barrel. Winchester barrels are now hammer forged, and that process was used when my particular gun was made. Twist is determined by the mandrel, and I don't see how the mandrel changes much from barrel to barrel?

Similarly, for barrels that are buttoned rifle, the twist is determined by the geometry of the carbide button. How can a carbide button go from 9 twist to an 8.5 twist from barrel-to-barrel? It just doesn't seem possible to me that these static parts are varying that much that quickly.

Obviously, tools wear, but barrel forging mandrel isn't going to wear to a faster twist. In the case of a carbide button, the twist rate will go down as the button wears, not get tighter. And such wear in both cases would be a slow process, anyway.

Only barrels that have some form of cut rifling could have much barrel-to-barrel variation. The big factory makers don't do cut rifling because it is too time consuming. Cut rifling is the purview of the custom barrel maker. And custom makers hold high tolerances, otherwise they go out of business.

Are you sure? The machine is pulling the ‘blank’ through the hammer forge, or pulling the button through the blank, and rotating as it pulls, isn’t it?

For hammer forging, the mandrel has a reverse image of the rifling permanently built into the mandrel at the specified twist rate. It can't be changed without changing the mandrel. The rotation of the mandrel has to be at the same rate as the twist rate of its rifling pattern.

A rifling button also has the rifling built into the button at a specified twist rate. It can't be changed without changing to a new button. The button can be rotated by an external force as it is pulled through, but the rotation rate must be compatible with the twist rate of the button lands.

For either method, if the mandrel/button has a 1:9 twist impressed on its surface, it would take huge amount of force to spin it at 1:8.5 as it passes through the bore.

From what I've gathered it isn't that cut and dry with respect to uniformity in the twist along the length of a particular barrel.

You have a lot of valid points and questions. Perhaps someone in the know will chime in. Perhaps the variations are in the mandrels themselves?

Not a barrel maker or machinist, I am not sure whether the barrel or the mandrel is rotated as the mandrel is pulled through the barrel on a button rifled barrel. But I would think that the machinery that rotates the barrel or mandrel, would vary, very little and the twist you get is totally dependent on the rotation rate the machine is set up for. From the pictures I've seen of button rifling mandrels, the part that actually impresses the rifling is very short and does not have much effect on twist rate, but twist rate being determined entirely by rate of rotation as it is pulled through the barrel. I may well be wrong about this. Maybe someone that has worked in the barrel making industry will post on this. RJ

Hard to see much because they are small, but below are photos of a forging mandrel (the gold colored piece in the first photo) and a rifling button (second photo). It looks to me that both have lands and grooves that do have twist to them. Much like a tap can only cut threads at its built-in twist rate, I think a mandrel/button can only engrave lands and grooves at its built-in twist rate. For a mandrel/button to twist at a different rate, the lands would have to "plow" sideways through the steel, requiring tremendous rotational force. I just don't see that happening. But I have no experience in this area of manufacturing and thus don't know for sure.

I agree the only way to answer my questions is for an actual barrel maker to weigh in. And, thanks for everyone's input.

As I said, I may be wrong on this and I was. Thanks for the info and photo's. RJ

You're correct. The button has the twist rate built in and it's attached to a long pull rod that has to turn at the same rate as the twist rate on the button or else you end up with a lot of scrap. Interestingly, the max O.D. of the button is .003" to .005" larger than the desired diameter of the grooves in the barrel since the barrel relaxes a little as the button passes through. The barrel has to be stress-relieved after buttoning.

The mandrels and buttons may be off a bit in their geometry causing the twist rate to vary from mandrel to mandrel or button. I am sure there is some allowed tolerance.

Cut rifled barrels are pretty much dead-on advertised twist, but button rifled barrels can vary by at least +/-.5".

A lot of good/bad info here based on WHAT????

Anyone ever think that whoever is doing the "twist rate check" is screwing up???? Just because a gunsmith does it doesn't really mean doodly.

HOW many of you have actually PRODUCED a barrel or seen it done...IN THE FLESH and not just looked online and RE-PETED what they read.

Ever think that gun makers might buy barrels by the TON with SPECIFIC tolerances that include variances otherwise a relatively cheap rifle would cost more than the Gross National Product if it were "PERFECT"

I've "tested/checked" the twist rates on MANY barrels and came up with several DIFFERENT numbers on the same barrel...all that means is the rod/handle bearings or "tight plug" just SLIPPED OR DIDN'T FOLLOW the little twirly's precisely.

Sometime I can't believe some of the "stuff" that purports to be "FACT" on some forums and "apples vs monkeys" doesn't even approach this mess.

And WHAT IS THE PROBLEM???? Barrel makers know what twist rates work best for the various calibers AND that twist rate is a COMPROMISE to cover SEVERAL BULLET WEIGHTS so Ya'll don't have to use ONE specific bullet nose profile, bullet length and bullet construction.

Ya'll have to get real here and look beyond the obvious because the obvious isn't really "OBVIOUS".

Good shooting.

Tight patches on rods are one thing, shooting and seeing signs of instability when there shouldn't be any are another.