Barrel twist question for 300wm.

[dfanonymous]

When Nemo was developing their long range 300wm they discovered that they had better long range accuracy with an 8 twist than with a 10 twist. They were running 215 Bergers.

Poorly constructed cup and core bullets may suffer from the faster twist. Most of today's bullets are much better constructed than even just 10 years ago. I don't think over stabilization is near the issue that it once was.

10" twist will not handle All the bullets currently avail. The 200g class and bigger lead free bullets will not work well in a 10" twist.

I see no down side to the 8" twist.

What was the barrel length

 

[RemHutch50]

I would appreciate some info on what happens or how it happens when you move from 1:10 to 1:8 in this situation. For my level and application, it would be nice to know if it's something I would benefit enough from worrying about it.

 

[dgarrett]

We get a bit spoiled here at almost everywhere we shoot is over 5000ft and we have very low humidity....Every 300 win I have shot with the exception of 1 would stabilize the 215gr and the 230grs.... The Sako was the one exception... It would not but would shoot the 190gr well... It had a 1in 11 twist...Dave

 

[105amatt]

My 300wm has a 1-11 twist Bartlein. It shoots everything from a 125 Nosler up to a 200 Accubond very well. I haven't tried any copper bullets, not a fan. My current favorite load is a 180 Sierra Gameking over H1000. I did try Berger's 210 Hvld and it didn't seem to care for those much.

Edit: I am at 1000ft elevation.

 

[RemHutch50]

Here at home, I'll be at 600'.

 

[dfanonymous]

I would appreciate some info on what happens or how it happens when you move from 1:10 to 1:8 in this situation. For my level and application, it would be nice to know if it's something I would benefit enough from worrying about it.

Well for starters, it depends on the length of the bullet (longer bullet equals more weight usually) but it's the length that plays a factor in stabilization. The heavier (mo longa boolets) will get more benefit from a faster twist to keep stabilization. That's the jist. Where I've been coming from is that plus or minus 10 grains of 200 and especially lesser grain projectiles is that going faster like a 8 twist on a .300, you'll end up getting more drag with the nose up belly flop that the bullet will do as especially passing transonic and ultimently less consistancy in your dope for the entirety of the cartridge to bullet dynamic performance. A faster twist looks good on stability calculator but it has other effects that just haven't been mentioned. Especially if you shoot low to high elevation in really cold to 120 degrees heat.

 

[entoptics]

I would appreciate some info on what happens or how it happens when you move from 1:10 to 1:8 in this situation. For my level and application, it would be nice to know if it's something I would benefit enough from worrying about it.

Hopefully this isn't too basic for you. Don't mean to insult your intelligence.

The short story is that you need a certain rpm to stabilize a bullet. It depends on the shape of the bullet. Short fat things like handguns require much lower RPM (50,000 rpm) vs long skinny things like a rifle bullet (200,000 rpm).

Unlike the car analogy, properly balanced tires generally don't have to spin at 200,000 rpm, nor are their aerodynamic properties changed with normal automobile tire RPMs.

With bullets, faster twist isn't always gonna be better. 2 undeniable reasons, 1 somewhat controversial reason, and a 4th that probably isn't that significant unless you go to extremes.

1) Spinning an out of balance bullet (slight variations in jacket thickness, heterogeneous lead core, etc) really fast can cause it to fly funny.

2) Thin jacket or soft lead bullets can literally come apart due to the centrifugal forces if spun really fast. Shooting 110 VMAX in my 300 win mag causes this.

3) "Over-stabilization". A bullet actually needs a little instability in flight, and doesn't point directly into the wind. I believe it generally is designed to point up a little (weight towards the back). If you spin it crazy fast, it will stay that way, even when the bullet starts to drop, instead of tilting and pointing generally in the direction it's traveling. At fairly long range, when the bullet is angling steeply back towards the ground, it won't tilt down enough, and basically is belly flopping towards the ground instead of tipping as it flies. This would obviously increase the drag, potentially in an unpredictable way.

4) Twisting the bullet requires energy and friction. If you take it to the extreme, a 1:2 twist barrel has considerably longer lands/grooves than a 1:20 twist (think straight line distance vs a curvy road). That generates pressure, reduces velocity, etc.

Where the rubber meets the road for you?

With well constructed, modern projectiles, in weights relevant to your rifle, 1 and 2 are probably not much of a concern. Neither is 4 when you're talking 1:8 vs 1:10. 3 comes down to preference, and how far you intend to shoot, as my understanding suggests "over stabilization" becomes a problem as the trajectory steepens at long distance.

You'd probably be fine with either a 1:8 or 1:10 or anything in-between. The longer the bullet the more RPM it needs. For 300 WM, only the REALLY long bullets (>215 lead core, >200 solid copper) would potentially be understabilized in 1:10, and unless you wanna shoot really light bullets (160 or less), 1:8 should be fine.

The only caveat to the above is that you absolutely can try for "perfect" stabilization, but only if you're certain you only wanna shoot a narrow range of projectiles. With long bullets, 1:8 might be a tiny bit better than 1:10, and vice versa for short bullets.

 

[RemHutch50]

Thanks entoptics. That helps to a degree. What's left for me is I have no clue as to what determines a long bullet vs not.
When(if) I ever get all the components together I would most likely try the ammo I know (have used in my other calibers). And hopefully will find a factory ammo that shoots well enough.

That being said, my first choices would be Hornady. Either the Superformance SST 180gr or the Precision Hunter ELD-X 200gr or maybe some of the Barnes TTSX stuff (180-220).
I hope to not have to go the reload direction as I don't have any equipment.
If there would be something wrong with this please let me know or offer any other choices.

Oh and if one of the twist rates would be best for my choices please let me know which.

 

[entoptics]

...What's left for me is I have no clue as to what determines a long bullet vs not.

...That being said, my first choices would be Hornady. Either the Superformance SST 180gr or the Precision Hunter ELD-X 200gr or maybe some of the Barnes TTSX stuff (180-220)...

Oh and if one of the twist rates would be best for my choices please let me know which.

In general, weight = length, as the bore diameter is fixed for the caliber, so the only way to add weight is to add length. The only significant variation on this is solid copper (Barnes TSX, Nosler E-Tip, Hornady, GMX, etc) vs lead core (just about everything else), as lead is considerably more dense than copper. A 180 gr copper bullet will necessarily be longer than a 180 gr jacketed lead bullet. A rough rule of thumb for 30 caliber is about 10% lighter. For example, a 180 gr solid copper bullet will be about the same dimensions as a 200 grain conventional copper jacketed lead bullet. A 180 gr lead will be the same size as a 165 copper, etc, etc.

Based on what you say above, none of your hopeful ammo choices will be outside the limits for either a 1:8 or 1:10 twist barrel. The heaviest solid copper Barnes TTSX stuff you mention might be too long for 1:10, otherwise, the rest sit squarely in the "sweet spot" IMO.

In general, factory rifles, firing factory ammunition, will not have any issues with the esoteric stuff discussed in this thread. Twist rate is something only the most thorough (nitpicky?) reloaders and long range shooters worry about. There are some rare exceptions (22-250 with 1:14 anyone?!?!), but the rifle/ammo manufacturers are generally working within the same parameters. No rifle company wants their guns to shoot crappy with "common" ammo, and no ammo company wants their ammo to shoot crappy in "common" guns.

In summary...Sounds like you won't need to worry about twist rate. Any rifle you pick because of attractive features that fit your needs, will have a suitable twist rate for any of the ammunition choices you mention.

 

[Wolf76]

I'd take a 1:9 if they make it. 1:10 is close to being ok on heavy bullets. 1:8 isn't necessary and costs you some velocity. 215gr is my limit in the 300wm. If more is needed, the 338 edge comes out of the safe.

 

[RockyMtnMT]

What was the barrel length

One of their techs is a buddy of mine. I'll check with him.

 

[Joefrazell]

I just ordered a bartlein 3b contour with a 9 twist. Would have gotten an 8 twist if I could have got my hands on one. My smith says 8 twist is best for the heavy bullets. I shoot the 215 bergers and they want a 10 twist or faster.

 

[RockyMtnMT]

Well for starters, it depends on the length of the bullet (longer bullet equals more weight usually) but it's the length that plays a factor in stabilization. The heavier (mo longa boolets) will get more benefit from a faster twist to keep stabilization. That's the jist. Where I've been coming from is that plus or minus 10 grains of 200 and especially lesser grain projectiles is that going faster like a 8 twist on a .300, you'll end up getting more drag with the nose up belly flop that the bullet will do as especially passing transonic and ultimently less consistancy in your dope for the entirety of the cartridge to bullet dynamic performance. A faster twist looks good on stability calculator but it has other effects that just haven't been mentioned. Especially if you shoot low to high elevation in really cold to 120 degrees heat.

I don't think your theory of overstabilization plays out in the elr crowd. They are running much faster than "needed" twist in order to pass the transonic range more cleanly.

From our shooting and testing we have seen no downside to running bullets in the range of 2.0 sg, and higher, calculated at sea level out to long range hunting ranges.

It was once thought that a bullet fired at marginal stability would be better for long range for the reason that you describe. So the nose will break over as the bullet trajectory does. I have hunted with bullets that are very accurate with marginal stability and have seen less than stellar results on game. Marginal stability will greatly increase the odds of bullet failure on game. Bullets tumbling on impact or not opening up due to yaw. The lower the rpm's the more quickly the bullet loses stability after impact causing the bullet to not track straight though an animal. This becomes ultimately important with quartering shots.

To the OP. As some others have said, your needs will most likely be met with any twist rate offered in factory rifles shooting factory ammo. I would recommend that you stay away from the 11" twist that are in some of the 30cal offerings. You should not rule out the faster twist that is available in the Browning. There is not a downside. Some have said that you will lose vel. Not enough to accurately measure or be noticeable from one rifle to the next. It may cost you ~25fps going from a 10" twist to an 8" twist. This is not enough to be noticed. You could get an 8" twist barrel that is faster than a 10" twist barrel just because of variation from one barrel to the next.

There is one effect of a faster twist compared to the slower twist than has not been mentioned, that actually happens. The faster twist will impart more spin drift than the slower twist with the same bullet. This is easily compensated for, so not really an issue.

My .02

 

[RockyMtnMT]

What was the barrel length

They were working with barrels from 16"-24".