I'm a little curious about the the lack of high BC low weight bullets. There are alloys that are very light and could apparently be fashioned into high BC bullets and yet we see nothing like this in the civilian sector.
Why not a 80 grain 30 caliber bullet with a BC of 1.0?
Why isn't there a line of bullets that are light yet long and pointy? I know Lapua makes a hollow base bullet, but I don't see many of these types around.
I'm not sure if it's a technical issue of a lack of market (orphan market).
It could absolutely be done but the costs involved would be greater and I believe that to be the biggest reason we don't see them.
I would like to see a 100 grain 6.5 bullet with a BC of about .600, that would be sweet in a 6.5/284!
Dave I could'nt agree with you more but only as a match type of bullet. You probably would'nt get much expansion from an alloy bullet and I can't think of too many thick skined animals that I would use light 80 gr bullets on. I read a couple of articles on tungsten alloy or core bullets and at some point they come close to becoming armor piercing so you start to cross the line of a class III projectile. Good old BATF rules. I'll try to see if I still have the articles or the reference. Also if I remember velocities were high causing excess barrel wear and the cost of manufacture was high where they would not be profitable.
I don't know about barrel wear from different alloys but would assume it'd take a fairly high speed twist to get the long light alloy bullets to stabilize. Maybe the twist rate would be too much for a long bullet.
The armor defeating bullet law only appplys to hand gund bullets you can make rifle bullets out of anything. to defeat most light body armor all you need is some speed. any lead bullet well do the job at over about 1700 fps.
The reason you don't see lightweight high BC bullets is pretty much the same reason you don't see Winston Cup Champions racing in cars that cost $2000. Money and speed go hand in hand. Ballistic efficiency and weight go hand in hand.
BC is the ratio of a bullet's sectional density to it's coefficient of form. Sectional density is the weight per cross sectional area. A high BC bullet that is lightweight would have to have a form factor that would make the bullet impractical. It's ogive would be greater than 30 calibers and to keep the weight down it would have to be made from something less dense than steel. (That long ogive increases the weight) It would have very unusual twist requirements. You would have to design your firearm around it.
If you are serious about this I will run a design that will try to get you an 80 gr., 308 bullet with a BC of over 1.00. Warning, it won't look like a bullet.
I spent about an hour on the computer last night, and the old phrase "You can't get there from here" applies.
The best I could get with an 80 gr. .308 bullet was a BC of .348. I kept increasing the ogive lengths and secant radii until I had a bullet that was 5.58" long with a 90 caliber secant radius. Because the volume kept getting larger I had to decrease the material density to keep the weight at 80 gr. That final bullet had a density of .050 lbs./ cubic inch, which is midway between nylon and aluminum. It also required a twist of 1 full turn in 1.5 inches to be stable, which is more like thread pitch than rifling. It would require some multi-increment gain twist to get an exit spin that fast.
The reason I stopped was that as the volume increased so did the surface area, and as I was decreasing the form drag by lengthening the ogive I was increasing the friction drag due to the added surface area. Further increases in the ogive resulted in the BC starting down.
So there it is. The best BC I could get with an 80 gr., .308 was .348. To get a higher BC would required more weight or going subcaliber and putting it in a sabot.