Light, high BC bullet

[Dave King]

Bullet design

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).

 

[PrimeTime]

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!

 

[TonyY]

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.

 

[Dave King]

Thanks for the replys.

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.

 

[p dog shooter]

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.

 

[Warren Jensen]

Dave,

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.

 

[Warren Jensen]

Just for you information,

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.

 

[Dave King]

Warren

Once again I'm grateful for your replies. Thanks for the time and effort to solve this mystery for me.

 

[cronhelm]

Warren,

Wasn't there some research into using very dense (denser than lead) materials for bullet construction in order to get very high BC values from otherwise conventional bullet designs?

Using a very dense material, the bullet weight could be maintained while the size and thus surface area (read drag) of the bullet could be reduced.

I'd be very happy with a 90-95 grain 6mm bullet with a BC of .8 or more. THAT would be a LOOOOOONG-range projectile.

Similarily a 200 grain .338 bullet with a BC approaching 1.0 would be an awesome long-range hunting projectile.

Peter Cronhelm

 

[steve smith]

Say something along the lines of depleted uranium. Maybe a nylon jacket or sabot. Say a 30 or 338 cal slug shaped like the Devel (muzzle loader) bullet (handloader #210 page 72) that has a polycarbonate tip.
A nonexpanding hunting bullet that has a high ballistic coefficient and can probably irradiate your meat for you all at the same time.

Warren
If I see this bullet in the near future come out under the Lost River Ball Tech new products. I expect to see some royalties.

 

[Warren Jensen]

Guys,

An 80 grain bullet weighs 80 grains. It does not matter how dense the material is. It will occupy less volume, but then you won't be able to optimize the front end. Remember there is a rule in bullet making. The OAL of the bearing surface(the shank) has to be at least as long as the bullet is wide, so that it doesn't try to get sideways in the bore. A .308" cylinder that is .308" long has a volume of .0229 cu. in. Uranium has a density of .676 lb/ cu. in. The shank would weigh 108.59 gr. You could do some type of wasp waste to reduce the volume and keep the shank OAL the same but it would screw up the aeros and reduce the BC. Area Rule works in supersonic jet fighters but is worthless in bullets. They do not have wings.

I have experience with poly materials. When you use them as the leading edge at Mach 3+ velocities they begin to change shape after about .5 seconds flight time. The temperature builds to above 500 deg. F. at the leading edge, dependent on the tip shape, and combined with the tremendous back pressure it is sufficient for even the most high temperature resistant poly materials to begin to flow. The result is at that point the BC begins to decline.

The only way that I can see to get a 1.0 BC with a 30 cal. 80 gr. bullet would be to add thrust in flight. If you machined a combusition chamber into the rear half of the bullet and a very precise nozzle, then filled this with solid propellant, maybe you could get enough thrust to get the equivalent of a 1.0 BC trajectory. But with this configuration you can forget anything like what we would call accuracy. The ignition delay parameters and the burn rates would not be nearly precise enough. You can get much better control with liquid propellants but that requires pumps and regulators. Besides that, all this fuel and stuff is extra weight.

If you use a sabot and subcaliber the 80 grain projectile you can do it. If it is spin stabilized it will only be as accurate as the shoe material will allow, which is generally not great accuracy. It is more accurate to fin stabilize a subcaliber round, but you need a very high sectional density, >.600, to overcome the drag the fins add. Also, you need a smooth bore.

The point I am meandering around is that it is tough to repeal the laws of math and phyics.

 

[Dave King]

Warren, I'm afraid you bringing these physical realities to light has burst a lot of bubbles.

I was absolutely certain we could come up with the 'magic' bullet.

Again, thanks for spending the time and effort to post these replies and the fortitude to put up with our sophmoric ballistics designs. I truly enjoy the posts and am greatful for the opportunity to have knowledgable folks to query. Thanks!!


One last item. Are you sure about the laws of physics? How about if we tried using the burnt stuff off the bottom of my wifes cookies as a sort of heat shield, could we get a hollow polycarbonate bullet to fly and not melt. (That burnt stuff is really heat resistant, those cookies are still RAW in the middle!)

Thanks

 

[steve smith]

Burned cookies as a heat shield! You might be on to something there Dave.

Warren
Actualy I was thinking of some thing along the lines of a bullet that has the aproximate shape of the heavy Sierra Match Kings in 30 and 33 cal. Maybe replace the polycarbonate tip with a hollow thin copper or aluminum tip. But mantain a flat front under the more aerodynamic sharply pointed tip. Something to give you at least a one caliber flat front surface. Keep the weight about even with the match kings, 220-250 for the 30 and 250-300 for the 338, or even higher if need be. You wouldn't get super high velocity but the BC would be awesome!

[ 07-25-2001: Message edited by: txhunter ]

 

[steve smith]

Just got to thinking that if you went with a heavier bullet you don't need a metallic tip. A polycarbonate tip sitting on top of a flat nose would work.