Which Twist? 1x9, 1x15, 1x20? [Archive] - Glock Talk

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dbow
06-10-2012, 10:32
Hey 10mm enthusiasts,
I live in the communist state of Maryland and need a 6" barrel and hot loads to hunt deer. All barrels i'm looking at will work, however, i was confused as to why each one had different twist rate.

Glock 6" is 1x9
LW 6" is 1x15
KKB is 1X20

Which one would shoot a underwood 200 grain jhp hot load better?

I did make a mistake with this with a rifle once. I purchased a 1x10 twist for a 243. Can't shoot 100grain bullets at all. I'm worried that a 200 grain wouldn't shoot well out of a 1x20 twist.

dm1906
06-10-2012, 12:00
I don't have Hornady's recommendation for rate of twist. According to the Greenhill formula, the minimum rate of twist is about 1:35. All this means is, anything faster than that (lower number) should stabilize. There are other factors to consider, but they are essentially irrelevant with the velocities, bullets and barrel lengths involved. Any of the barrels you list should be at least adequate (although 1:9 seems too fast, but the "rifling" design is different). The non-Glock barrels will likely produce better terminal bullet performance, due to the lower twist rate, rifling design and chamber dimensions. Almost all handgun bullets are very forgiving when it comes to twist rates, within subsonic to transonic velocities (650~1250 FPS). Get too fast with a very high rate of twist, and other issues can occur outside the formula, such as friction loss (rifle stripping/skipping), but this is not an issue with almost anything we'll discuss in regards to these pistols and common bullets.

The only time I've ran into issues with a twist rate was developing a .44M round for an older Win. 94 rifle. The twist rate of the barrel was 1:38, so some bullets were less than ideal. It was so bad with some rounds, you could actually hear the bullet tumble at about 50 yds. Ziiiiing..... Couldn't even find the target with those. Later rifles are 1:20, so no problem with them.

dbow
06-11-2012, 16:45
Thanks for the info dm1906. I think it would be kinda nice to see the top 2-3 aftermarket barrel companies do some tests using hot loads on different twist rate barrels.

I think kkm has it figured out. Thought i remember hearing that they test different ratios, but i wonder if they using hotloads?

dm1906
06-11-2012, 20:00
I don't know that one is better than the other. Just stating my opinion (after the science) according to my experience. Settling on an extreme, rather than a happy medium, usually leaves you operating in that extreme. A slow rate may optimize for one range of bullet weight, length and velocity, but often becomes ineffective at the opposite end of the scale. 1:20 may be better for some bullets, but may not stabilize others as well. It may be the magic number. I don't know, yet. Either aftermarket barrel performs well, in any case, so I'd not consider it a sole deciding factor.

TDC20
06-11-2012, 21:22
I think it would be kinda nice to see the top 2-3 aftermarket barrel companies do some tests using hot loads on different twist rate barrels.

I think kkm has it figured out. Thought i remember hearing that they test different ratios, but i wonder if they using hotloads?
I remember reading somewhere that a rifle with a marginal twist rate will stabilize the same bullet better if fired at a higher velocity. The idea is that the bullet that leaves the barrel with the most velocity is also spinning faster, therefore it becomes more stable. It would seem to make sense.

I don't know if this is actually true or if it applies to handguns, so take it with a grain of salt.

dm1906
06-11-2012, 22:25
I remember reading somewhere that a rifle with a marginal twist rate will stabilize the same bullet better if fired at a higher velocity. The idea is that the bullet that leaves the barrel with the most velocity is also spinning faster, therefore it becomes more stable. It would seem to make sense.

I don't know if this is actually true or if it applies to handguns, so take it with a grain of salt.

Actually, no. Unless you are on the ragged edge of the formula, as there is a little fudge room to account for other variables, such as climate, baro-pressure, temp, humidity, density, etc. The margin is very narrow. The Greenhill Formula is very accurate and widely accepted as a standard. Higher velocity requires a higher RPM. They track almost parallel up to about 2800 FPS (RPM requirement increases), which is when the math changes a bit, but not near a factor for us shortgun shooters.

dbow
06-12-2012, 11:33
Actually, no. Unless you are on the ragged edge of the formula, as there is a little fudge room to account for other variables, such as climate, baro-pressure, temp, humidity, density, etc. The margin is very narrow. The Greenhill Formula is very accurate and widely accepted as a standard. Higher velocity requires a higher RPM. They track almost parallel up to about 2800 FPS (RPM requirement increases), which is when the math changes a bit, but not near a factor for us shortgun shooters.


i agree, i tried to shot a hotter load 100 grain in my 243 and it did nothing. I'm surprised at how touchy rifles are with twist ratio compared to handguns.