That is BS BT. Look at the manufacturer's over the last 15-20 years and what barrel twist rate's they produced. 1-7 vs 1-9. That should tell you something.

M4 carbine barrel was made in error (skinny under the hand guards). It was a mistake. Yet they pumped those out by the millions, and still make them today.

1-9 is the ideal twist for Joe Nobody that shoots 55-62 grain plinking ammo, which is just about everybody.

How many civilians are shooting long tracer rounds? Which is the reason 1-7 went into production in the first place.

I wonder why Ruger and Smith and Windham went with 1-8 and 1-9 for the majority of their rifles? It’s almost as if… as if… they did their homework and found the ideal twist rate for the majority of what their customers would be shooting.

Serious question, would 1 in 9 give you longer tool life?

quote:

Originally posted by OttoSig:
Serious question, would 1 in 9 give you longer tool life?

Since you said you're serious, I'm only going to offer what I have found when studying up on ARs.

There's an optimal twist rate for a range of bullet weight. 1-9 twist rate gives the optimal spin to a 55 grain. A faster twist rate makes the smaller grain unstable. A heavier grain bullet which apparently is longer requires a faster twist rate for more stability.

Understanding Twist Rate

quote:

Originally posted by OttoSig:
Serious question, would 1 in 9 give you longer tool life?

Uncertain of your definition of "tool", but I'll try some options. Starting with the tool that makes the rifling in the barrel. I can't see how it makes a difference with a hammer forged barrel, as one mandrel lasts a long time. With cut and button rifling, there is definitely some form of indexing machine which twists the barrel faster for faster twists, as the rifling is being manufactured. I have not seen any manufacturer discuss that on their website, a forum, or a general information video. In theory the faster twist cutting process stresses the rifling machine a bit more, but who knows if it really makes a difference to rifling machinery life.

On to the barrel itself as a tool. In theory the lands of a faster twist barrel will wear out a bit more quickly than a slower twist barrel. The faster twist lands must do more "work" in the first part of the barrel, imparting more of the bullet's kinetic energy into spin energy. I'm guessing that barrel throat wear from the hot gasses of the cartridge eat away at the steel much faster than the friction of bullet-against-lands.

On to the bullet itself as a tool. Of course a bullet is one-use tool. But in really high velocity chamberings, using thinly jacketed bullets, this can be a concern. The lands can weaken the jacket a bit, then uber-high rotational forces spin the bullet to pieces. I originally heard about this with high-velocity centerfire .224 bore guns, with some relatively fragile varmint bullets. Never saw it occur, however. But I have seen it occur in Extended Long Range matches, where guys are using big magnum cartridges to push 7mm and .30 caliber bullets to high speeds. I was spotting shots and the bullets evaporated into gray dust clouds maybe 50-100 yards down range.

But my guess is you're looking for "tool" as the tooling that forms the lands/grooves in barrels. I doubt that twist rate makes any significant difference in production life.

Simple but complex.
An absolutely unmodified factory gun that doesn't have a kabillion marketing videos that make it look slick and cool. Pistol AR. SIG 300Blk. Zero cool gadgets. Rittenhouse should tell you why.
Bright white light of very high quality
Laser designator of any type, sighted in at 50ft.
Sling
Single set of duplexed mags
Electronic muffs, safariland hanging on gun to be donned immediately

At LEAST 2K rounds of ammo downrange of the same type as those in the duplexed mags.

I must have confidence in the weapon,twist rate is not a consideration - I'm defending my home, those distances where I can realistically claim self defense are small. No aftermarket mods.

The above graph was displayed in a previous post. After viewing it in detail, I find it somewhat confusing or incorrect.

As we all know, the current Swiss Army rifle is the STGW 90 and the current Swiss Army issue rifle ammunition is the GP90. The Swiss being Swiss, optimized the STGW 90 rifle to fire GP90 ammo. The STGW 90 barrel has a 1:10 twist while GP90 ammo has a 63 grain bullet. According to the above graph the STGW 90 barrel is not optimal for GP90 ammo. But how could that be? Either the Swiss Army has screwed up or the graph is incorrect.

According to the ballistician Bryan Litz, a rifling twist rate that’s faster than required to stabilize a bullet of a certain length doesn’t make the bullet unstable in flight. I have fired countless 55 grain bullets from 1/7 twist barrels with absolutely no sign of instability when they hit the target at various distances. What an unnecessarily fast twist rate does or can do is increase the effects of any irregularities in the bullet on its precision. That is, if the bullet isn’t absolutely perfect in every way (an impossibility even today), the faster it spins the more it will deviate from the desired path to the target. He points out that’s why benchrest shooters who are usually concerned only about maximum precision at relatively close ranges mostly shoot shorter bullets (i.e., with flat bases rather than boattails) from slower twist rate barrels.

That issue and others relating to maximum long range precision such as minimum wind drift are not things that will ever be important to the average AR shooter, and especially not to someone who is relying on a particular gun for short range self-defense.

For maximum wounding effects with bullets that rely on tumbling for those effects, slower twist rates are theoretically better because the bullet will upset faster in the target. But in actual fact a 55 grain M193 bullet from a 1/7 inch barrel is plenty devastating, and part of that is because of its higher velocity: speed (often) kills. That load may not be optimum for military combat these days for a variety of reasons, but if your home invader stands there and laughs off the first shot to his lung and arteries, shoot him again and again and again. That’s one of the advantages of the 5.56/223 AR: it’s possible to do that very, very quickly.
(That doesn’t mean that I consider the M193 to be the best self-defense load available, but it’s dam’ good. And if we’re stuck with that ammunition and want the absolutely best wounding effects from it, change your barrel to 1/12".)

And as a bit of background, it’s been reported more than once that the reason the military settled on the 1/7" rifling twist rate was because it was necessary to stabilize the long tracer bullets in arctic air temperatures.

The $600 rifle with $400 of ammo ran through it.

quote:

Originally posted by MG34_Dan:
Either the Swiss Army has screwed up or the graph is incorrect.

Or we could have a false dichotomy and neither is true.

The chart above is based on bullet weight and is true only for conventional jacketed bullets with lead cores. Further, it refers to “best,” not necessarily required or unusable.

My limited research indicates that the “5.6mm” GP90 bullet has a full lead core (except for a copper plug at the base, evidently to prevent loss of lead vapor). A somewhat similar bullet is the Lake City 62 grain FMJBT (M855) bullet which Litz says requires a minimum twist of 1/9.1" for stability. But similar is not the same.
Without the M855’s slightly lighter steel “penetrator” in the tip inside the jacket of the bullet, the GP90’s bullet should be a bit shorter than the U.S. bullet and therefore would be stabilized by a slightly slower twist rate.

Several references about the GP90 5.6mm cartridge state that it was “optimized” for the 1/10" rifling twist rate of the Swiss military rifle, but without any further description of what that means (that I could find). As I mentioned above, a slower twist rate that still stabilizes the bullet sufficiently is better for practical precision. In addition, wounding effects are in theory at least somewhat greater. I am, however, always a little suspicious of identical statements that appear in multiple different sources especially about something like a foreign military weapon system, and double especially when there are even slight discrepancies among them.

The original 5.6 GP90 bullet had a nickel jacket, but that was later changed to “tombac” which is evidently the same as our more familiar gilding metal copper alloy. Some descriptions of the ammunition claim that the change was made because the nickel caused excessive bore wear, while others state that it was because nickel caused excessive bore fouling. The latter seems to be much more likely because it was found to be true by the US military nearly a century or so ago. In addition I’ve found myself that nickel fouling is much more difficult to remove from a barrel because copper-cutting solvents don’t work well on the metal. I cite all that as an example of how nonexpert journalists who really don’t understand what they’re reporting about can often get things wrong when all they can do is parrot what they’re told (to some degree, anyway).

And finally, there’s always the danger of the “other agency” syndrome affecting things. I could cite numerous examples from my own experiences here and abroad, but sometimes there is the idea that a somewhat mythic organization like the Swiss military will automatically be smarter than the people we’re more familiar with. But as the song says, “It ain’t necessarily so.” Because it would be mostly speculating, not to mention be even more tedious than my comments thus far, I won’t go into my reasons, but could the Swiss Army have screwed up? Yup.

If I had the money a KAC SR-15 would be on the short list.
Sometimes they really are worth $2,500.

Pretty cool video of a physical on a new rifle.