Barrel length question.

[GlennGTR1]

If one were to shoot a 223 rem, with a twist rate of one in nine, would it still stabilize the heavier 65-70gr weight bullets in a 16.5 inch barrel? I am looking at the Ruger Hawkeye compact as a truck, scout, kicking around varminter. The rifle handles and points very well, just a little concerned about the short barrel length with the heavier bullets in 223 cal.

 

[RonAKA]

Only velocity would be affected, and it does not have a major effect on stabilization. If you are not close to instability with a longer barrel, it is unlikely to be unstable with a shorter one.

 

[HillbillySniper]

Only velocity would be affected, and it does not have a major effect on stabilization. If you are not close to instability with a longer barrel, it is unlikely to be unstable with a shorter one.

+1

 

[Tozguy]

Would you please explain how a lower velocity which obviously means slower bullet spin could not have an impact on stability. Some bullets shoot best when only barely stabilized. Velocity has to be kept up to maintain accuracy. How much velocity can you afford to loose in a case like that?
I suggest that before cutting a barrel one does a bit of calculation based on bullet manufacturer's recommendations on what it takes to stabilize the bullet you plan to shoot.

 

[DCRYDER]

I've got the pre-Hawkeye SS/Lam 223 Compact, and used to have the same gun in .308. You are right, for a truck gun or walking/stalking gun they are very nice. I had no idea they now come in 1-9" twist! I'll have to check mine out, though it's probably an old 12" twist.

I agree with RonAKA, as efficient as the .223 is I very seriously doubt that there will be enough velocity lost to affect stability. Most recommended twist rates are conservative anyway.

 

[Steve Blair]

Would you please explain how a lower velocity which obviously means slower bullet spin could not have an impact on stability. Some bullets shoot best when only barely stabilized. Velocity has to be kept up to maintain accuracy. How much velocity can you afford to loose in a case like that?

Ron's comment was correct. Velocity is the least significant factor in bullet stability. It only has an effect if stability is marginal. The most significant factors are, in order:

Bullet length vs. twist rate
Temperature & altitude (air density)
Velocity

This can be easily verified by calculating bullet RPM. An 8" twist is about 11% faster than a 9" twist. Assuming a 3300 fps muzzle velocity; velocity would need to increase by over 360 fps to equal the rotational speed from the faster twist. Both are linear relative to RPM.

Velocity changes have never caused me a stability problem but I have been bitten by load development at warm temperatures and hunting at freezing temps.

 

[Tozguy]

Steve, The calculation you mentionned is along the lines of what I was referring to. If I were betting on the outcome I agree that it is 'unlikely, not major, least significant, very seriously doubt' that bullet stability would be compromised. However, that would not be enough for me to go ahead and cut the barrel. We don't even know what bullet length we are talking about and that is at the top of the list of factors. Even if velocity is third on the list it is still a factor. Why not use the calculation tools available if only to confirm the perspective that stability will be OK? My point is that when we cut a barrel, we can't weld the stub back on if we get a surprise down the line. So why not run the numbers, it might keep someone else from getting 'bitten'.

 

[RonAKA]

Would you please explain how a lower velocity which obviously means slower bullet spin could not have an impact on stability. Some bullets shoot best when only barely stabilized. Velocity has to be kept up to maintain accuracy. How much velocity can you afford to loose in a case like that?
I suggest that before cutting a barrel one does a bit of calculation based on bullet manufacturer's recommendations on what it takes to stabilize the bullet you plan to shoot.

Velocity does have an impact, but it is not major. Also if it OK at the muzzle it gets better as the bullet goes down range, as spin does not slow down as much as forward velocity.

I used the Border Barrel McGyro program to calculate stability of a Berger 70 VLD using Berger Specifications. I did have to guess at the base diameter (0.200"), but it should be reasonable. Look at the lower graph at this link. It shows stability in a 9 twist vs velocity. In a 24" velocity would be about 3100, while in a 16" perhaps 2800? If so stability would drop from 1.33 to perhaps 1.32? Hard to read, but I would suggest an insignificant change. 1.4 is considered ideal by some, but this 1.33 is with Berger's recommended twist of 1 in 9.

My personal experience with boat tails is that they actually do go unstable at around 1.0 to 1.05 using this McGyro program. If you look at this updated graph, assuming -40F for temperature (ouch!!), at 2800 you are at about 1.08, and likely on the edge of real instability. But if you are shooting at -40F, then we could discuss whether the bullet or the guy behind the gun is unstable!

 

[Steve Blair]

Steve, The calculation you mentionned is along the lines of what I was referring to. If I were betting on the outcome I agree that it is 'unlikely, not major, least significant, very seriously doubt' that bullet stability would be compromised. However, that would not be enough for me to go ahead and cut the barrel. We don't even know what bullet length we are talking about and that is at the top of the list of factors. Even if velocity is third on the list it is still a factor. Why not use the calculation tools available if only to confirm the perspective that stability will be OK? My point is that when we cut a barrel, we can't weld the stub back on if we get a surprise down the line. So why not run the numbers, it might keep someone else from getting 'bitten'.

You are correct. I was not suggesting that determining the stability prior to committing an irreversible act was a bad idea. It is absolutely the way to do it. My point was that velocity is only relevant if bullet stability is borderline.

I always run many simulations in QuickLOAD and use bullet stability calculators, as well as reviewing my historical data, before deciding on a specific barrel length and twist. My rifles are usually designed for a specific purpose and have a narrow bullet and velocity range in mind, making the choices easier.

I think we agree and I apologize if my post was ambiguous.

 

[Tozguy]

Thanks guys, Glenn, does this help?

 

[Steve Blair]

QuickLOAD tells me that >2800 fps is attainable in 16.5" with a Berger 70g VLD, loaded to magazine length. In ICAO standard temp of 59°, that would provide a stability factor of 1.329 in a 9" twist. The Sierra 69g MK is much higher, over 1.6. Glenn should not have a problem in the 16.5" barrel.

 

[jonbearman]

Have you ney sayers ever heard of a dpms sweet 16 incher.They shoot up to in some 75grain pills.I seriously doubt he is going to benchrest compete with this gun.I would shoot sierra 69 matchkings if you are prarie dogging or woodchuck hunting.I have shot coyotes with them and they drop like cement.We cant get real technical all the time , especially if the poor guy just wants to dispatch varmints.

 

[Tozguy]

Jon, Just wondering what twist rate the 16 '' DPM uses. Hope Glenn will tell us if he got more than he wanted from his question.

 

[jkats]

dpms sweet 16 has a 1 in 9 twist

 

[GlennGTR1]

Nope, got just the right amound of info. Thanks for all the input. Will be getting the compact and then tweaking it for maximum accuracy.