Why round nose bullets for subsonic
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Re: Why round nose bullets for subsonic
There's a few reasons. RN bullets are flat base, which make the overall bullet length shorter. The bullet being shorter allows it to stabilize in a given twist rate. If you took a BTHP in the same weight, it would be much longer and harder to stabilize in the same twist. Remember, it's the bullet length that determines the twist rate, not the weight of the bullet. The longer the bullet (and normally higher in weight), the faster the twist needed.
Another reason is you are going to a max velocity of about 1050 to 1100 fps. Most RN bullets are in the upper weight range for a given caliber. You get a higher weight bullet at a given speed which gives you more energy on target.
There's a few reasons. RN bullets are flat base, which make the overall bullet length shorter. The bullet being shorter allows it to stabilize in a given twist rate. If you took a BTHP in the same weight, it would be much longer and harder to stabilize in the same twist. Remember, it's the bullet length that determines the twist rate, not the weight of the bullet. The longer the bullet (and normally higher in weight), the faster the twist needed.
Another reason is you are going to a max velocity of about 1050 to 1100 fps. Most RN bullets are in the upper weight range for a given caliber. You get a higher weight bullet at a given speed which gives you more energy on target.
Re: Why round nose bullets for subsonic
And the BC effects the bullet "less" than at higher speeds...not exactly but it's not as big of an impact.
And the BC effects the bullet "less" than at higher speeds...not exactly but it's not as big of an impact.
Re: Why round nose bullets for subsonic
NASA found that the most stable object traveling at subsonic speed is something shaped like a raindrop.
NASA found that the most stable object traveling at subsonic speed is something shaped like a raindrop.
Re: Why round nose bullets for subsonic
I have loaded a lot of subs in .308 and 7.62x39, and real world application is, it is definatly easier to stabilize a RN bullet. Also when I stopped trying to load pointed bullets to sub speeds, my ES and SD instantly got much better.
I have loaded a lot of subs in .308 and 7.62x39, and real world application is, it is definatly easier to stabilize a RN bullet. Also when I stopped trying to load pointed bullets to sub speeds, my ES and SD instantly got much better.
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Re: Why round nose bullets for subsonic
The round nose has the bulk of it's weight mostly even front to rear. A pointed bullet when shot subsonic needs way more twist to keep it stable, vs the rd nose. I've had good luck with 175smk's when pushed to max subsonic speeds. A friend has a 16" 5 twist .308win barrel that is the best I've ever seen for 190, an 175smk's. Don't know who made it, as he picked it up at a show years back.
175's an such fly better, loaded backwards.
Cast bullets work very well also, plus you can set the hardness anywhere you want. The softer they are, the bigger they grow on impact.
The round nose has the bulk of it's weight mostly even front to rear. A pointed bullet when shot subsonic needs way more twist to keep it stable, vs the rd nose. I've had good luck with 175smk's when pushed to max subsonic speeds. A friend has a 16" 5 twist .308win barrel that is the best I've ever seen for 190, an 175smk's. Don't know who made it, as he picked it up at a show years back.
175's an such fly better, loaded backwards.
Cast bullets work very well also, plus you can set the hardness anywhere you want. The softer they are, the bigger they grow on impact.
Re: Why round nose bullets for subsonic
Everybody knows a bullet has to be spun to be stabilized but many overlook the role of the shape of the bullet, particularly as it affects the Center of Gravity and the Center of Pressure. The relationship of CG to CP is central to the stability of any moving object, as this illustration from a model rocket maker indicates:
The classic example of CG-vs-CP is an archer's arrow. Shoot an arrow point first and it has extremely good stability, even though it has little or no spin. That's because it's balance point is somewhere near its middle but the drag produced by the fletchings mounted all the way at its tail end pull its Center of Pressure <span style="font-style: italic">WAY BACK</span> behind its Center of Gravity. The further to the rear of the CG that the CP is manifested, the more "positive static longitudinal stability" the arrow (or any other moving object) will have. But shoot it fletchings-first and it will be radically unstable. No matter how hard you spin it, it will want to turn around and put the CG back in front of the CP.
The balance point of a round-nosed, flat-based bullet is fairly close to its midway point, which puts its CG and CP pretty close together. Because they're close together, all they need is a relatively low rate of spin to keep them stabilized. But making the nose of a bullet longer, more tapered and more aerodynamic means removing material (and weight) from the front half, which means the CG is shifted further to the rear.
Spin or no spin, moving the CG that far aft of the CP would make for a pretty radically unstable bullet if it weren't for what happens when the bullet bumps into the sound barrier. Fortunately for shooters, CP is an aerodynamic property and all aerodynamic properties are affected by the shock wave that always envelops a bullet when it reaches the speed of sound. That shock wave drives the CP toward the rear of the bullet and dramatically improves longitudinal stability in the doing so it takes a much lower rate of spin to keep the pointy end in the front. That means that some bullet designs with a CG that is too far aft to be stable at subsonic velocities <span style="font-style: italic">can be</span> stable when supersonic, even at the same RPMs. Which also explains why the maximum effective range of most rifles is considered the greatest distance at which it will remain at or above the speed of sound. Because once it loses SoS, it loses the shockwave and the CP shifts forward, dramatically reducing stability.
Sorry for the long-winded explanation but part of the answer to your question is understanding why it is that supersonic bullets can tolerate a long, pointy nose when it does such horrible things to bullet's stability.
Everybody knows a bullet has to be spun to be stabilized but many overlook the role of the shape of the bullet, particularly as it affects the Center of Gravity and the Center of Pressure. The relationship of CG to CP is central to the stability of any moving object, as this illustration from a model rocket maker indicates:
The classic example of CG-vs-CP is an archer's arrow. Shoot an arrow point first and it has extremely good stability, even though it has little or no spin. That's because it's balance point is somewhere near its middle but the drag produced by the fletchings mounted all the way at its tail end pull its Center of Pressure <span style="font-style: italic">WAY BACK</span> behind its Center of Gravity. The further to the rear of the CG that the CP is manifested, the more "positive static longitudinal stability" the arrow (or any other moving object) will have. But shoot it fletchings-first and it will be radically unstable. No matter how hard you spin it, it will want to turn around and put the CG back in front of the CP.
The balance point of a round-nosed, flat-based bullet is fairly close to its midway point, which puts its CG and CP pretty close together. Because they're close together, all they need is a relatively low rate of spin to keep them stabilized. But making the nose of a bullet longer, more tapered and more aerodynamic means removing material (and weight) from the front half, which means the CG is shifted further to the rear.
Spin or no spin, moving the CG that far aft of the CP would make for a pretty radically unstable bullet if it weren't for what happens when the bullet bumps into the sound barrier. Fortunately for shooters, CP is an aerodynamic property and all aerodynamic properties are affected by the shock wave that always envelops a bullet when it reaches the speed of sound. That shock wave drives the CP toward the rear of the bullet and dramatically improves longitudinal stability in the doing so it takes a much lower rate of spin to keep the pointy end in the front. That means that some bullet designs with a CG that is too far aft to be stable at subsonic velocities <span style="font-style: italic">can be</span> stable when supersonic, even at the same RPMs. Which also explains why the maximum effective range of most rifles is considered the greatest distance at which it will remain at or above the speed of sound. Because once it loses SoS, it loses the shockwave and the CP shifts forward, dramatically reducing stability.
Sorry for the long-winded explanation but part of the answer to your question is understanding why it is that supersonic bullets can tolerate a long, pointy nose when it does such horrible things to bullet's stability.
Re: Why round nose bullets for subsonic
p = mv. That is the equation for momentum. Momentum is what is going to make critters tumble. We are at a fixed velocity, so the only way to get more momentum is to up the mass. B.C. won't matter since we are going slow, so you make it a round nose to be able to fit the most mass in the bullet and have a reasonable C.O.L.
p = mv. That is the equation for momentum. Momentum is what is going to make critters tumble. We are at a fixed velocity, so the only way to get more momentum is to up the mass. B.C. won't matter since we are going slow, so you make it a round nose to be able to fit the most mass in the bullet and have a reasonable C.O.L.
