Have we maxed out BC?

[Steve Blair]

How do they measure velocity every 100 yards out to 1000 yards? Do you really think this is what they do. Cost for every bullet they make?
The BC is not a constant it is continually changing with the velocity down range. In the Sierra manual they give four BC for the 107 gr. Match King #1505 bullet depending on the velocity range it's in. Some long distance shooters complained to Sierra that there come ups didn't match the BC. Sierra recalculated the BC and apologized.

[br]
It is not necessary to measure every 100 yards. Minimally, only two chronographs are needed. If G7 B.C. is used, the variance is much less and can be largely discounted. Sierra insists on clinging to G1 B.C., which is appropriate for flat base, short nose bullets, not the long nose boat tails we shoot at long range. Here is an article that Bryan wrote for this site explaining the difference. You should also do some more investigation of the history of both coefficients and why they are preceded by "G". Very interesting stuff. [br]
http://bulletin.accurateshooter.com/2013/01/g1-vs-g7-ballistic-coefficients-what-you-need-to-know/

 

[Webster]

Read it. Bryan says he used acoustic sensors every 200 yards to 600 or 1000 yards to determine BC on several long range bullets. I'm sure every long range bullet doesn't get this test. The bottom line whether you shoot short or long distance is you have to shoot the bullet in your gun and see how it performs. Enough said. Lets drop the subject.

 

[Brians356]

It was Arlo Guthrie who said that after you take LSD you realize there's no such thing as "in tune".

There's no such thing as an accurate and absolute BC value. Let's start with that. And end with it.

 

[M14AMU]

I think MOST BC's are determined by SALES HYPE!!

 

[mshelton]

I thought BC was the powder stuff I took after a hard night of drinking.

 

[amlevin]

lathe-turned solids. The cost has been high,

Using CNC "Screw Machines" the costs could be significantly lower if mass production kicked in. When you think of it a solid bullet is no more complex to produce than some of the items currently produced using "automatic lathes" which are packaged and in the hardware section of home depot. The alloys used would be most of the cost. Consider the methods used to create conventional bullets today with the forming of jackts, cutting of cores, assembly, swaging, etc, versus feeding "wire stock" into a machine and have it spit out "turned" bullets.

 

[243Mendoza]

...
Bullet designers are working hard to make bullets that more closely resemble the Sears-Haack Body which is the most efficient aerodynamic shape. Essentially a bullet with "points" on both ends. ...

Such a bullet would have to be enclosed in a sabot which brings its own problems when discarding.

 

[Catfur]

...
Bullet designers are working hard to make bullets that more closely resemble the Sears-Haack Body which is the most efficient aerodynamic shape. Essentially a bullet with "points" on both ends. ...

Such a bullet would have to be enclosed in a sabot which brings its own problems when discarding.

Not to mention wouldn't stabilize at any realistic twist rate. Tank sabot rounds are fin-stabilized, because no twist rate will stabilize them.

 

[mac86951]

At what point does increased mass and slower velocity actually hurt performance?

That is the real question and you see it tested on the 1k line year after year.
First off, the 25x59 round is a muzzle velocity of 1390fps and still anti-material out to 1.2 miles... Must be a HUGE arc in the ballistic path though, not too unlike a catapult.

It is easy for most shooters to forget that BC is really the coefficient for ballistic travel. Its simply a function of mass and drag. Higher BC means higher density materials in the same bullet shape, or reduced drag. I don't believe the hype at all about bucking the wind with higher BC. The BC is about the nose to tail aero, not the cylindrical crosswise aero, but mass is a more prominent part of that function and higher BC usually means more mass too, so often higher BC means better wind bucking too. Really equal mass bullets with different BC will need different minimum twist rates to stabilize flight.

Ultimately, there is a sweet-spot between trajectory ballistic arc, flight path stability, wind effects, and shooters ability to repeat all; or better described "manipulate all" such that the paths all intersect at the target location.

While bullets are still lead, yes there is a limit. Look at 1k .308 for example. Starting with 173gr in the M1 Garand for rules reasons, but when switching over to .308 the 168gr was king for a long time. Then many shooters moved to 190-208gr for trials and found powder/case volume to be an issue, and currently are back to a 155gr to balance velocity and BC. Balance being the key word.

I'll go out on a limb and say that all else being the same, higher mass, lower velocity is better always, but limit 1 is seating depth, otherwise we'd be loading 90gr Sierras at mag length in our .223. Limit 2 is barrel twist, at what point is the bullet unstable, meaning new barrel is needed? Limit 3 is case design, at what point is the case shape and volume the limit along with barrel length and powder burn rate. Finally the primer's ability to ignite the powder. Naturally, these are in no order, but all are already variables in our owned ballistic solution finders, tuning is about finding which one is most critical which means it is up to you to determine where the limit really is.

-Mac

 

[243Mendoza]

...
Bullet designers are working hard to make bullets that more closely resemble the Sears-Haack Body which is the most efficient aerodynamic shape. Essentially a bullet with "points" on both ends. ...

Such a bullet would have to be enclosed in a sabot which brings its own problems when discarding.

Not to mention wouldn't stabilize at any realistic twist rate. Tank sabot rounds are fin-stabilized, because no twist rate will stabilize them.

I suspect a Sears-Haack projectile will need less twist rate than a conventional projectile of same length since the cg will be nearer the center of pressure.

 

[CPorter]

Measuring velocity at several ranges isn't all that hard, even I can do it. I have two CED M2s and reasonably accurate firearms.

I see 3D printing being explored in bullet making and high BC low volume projectiles. Already ready guns are being made using laser sintering techniques. Making bullets with gilding metal or copper jackets and tungsten cores that are locked together through sintering. How fine can they make a tungsten powder?

Or maybe make a tunsten core then use chemical vapor deposition or plating

 

[amlevin]

Such a bullet would have to be enclosed in a sabot which brings its own problems when discarding.

Not to mention wouldn't stabilize at any realistic twist rate. Tank sabot rounds are fin-stabilized, because no twist rate will stabilize them.

The MAIN reason that the "Sabot" and "Super Sabot" as well as the KEW (Kinetic Energy Weapon) are fin stabilized is that the Main Guns on tanks are now smooth bore. This change started in the 60's (on the Russian side) due to barrel wear in rifled barrels. You think us "target shooters" have issues with "retreating throats", you should look down the breach of a tank's main gun barrel, especially if it was used a lot for training.

 

[Steve Blair]

The MAIN reason that the "Sabot" and "Super Sabot" as well as the KEW (Kinetic Energy Weapon) are fin stabilized is that the Main Guns on tanks are now smooth bore. This change started in the 60's (on the Russian side) due to barrel wear in rifled barrels. You think us "target shooters" have issues with "retreating throats", you should look down the breach of a tank's main gun barrel, especially if it was used a lot for training.

[br]
Not true. Royal Ordnance L7, L11 and L30 guns are all rifled and shoot APFSDS rounds just fine. In fact, there are sabot petal separation advantages to using a rifled gun. The primary advantage of a smooth bore is barrel life. Rifled guns can fire HESH rounds which smooth bores cannot. HESH are useful against a variety of targets. The RO L30 with CHARM3 ammunition family is as good as any tank gun extant. The Germans deliberately cripple themselves by refusing to use DU penetrators for political reasons. As if killing your enemies has any criteria other than the base object.

 

[Laurie]

There is another reason for adopting the smoothbore tank cannon barrel form I believe. A percentage of the propellant charge energy is 'wasted' in inducing the spin given to the projectile in any rifled barrel, quite significant when you're into the projectile weights used here. A smoothbore allows higher MVs, or the same MVs with a smaller charge. Whether the absence of rifling induced torque on the gun platform is a plus as well?

 

[Steve Blair]

Well, as you know, RO and UK MOD have argued against those premises for decades, promoting rifled tubes as the better choice. Challenger retains them to date, despite some occasional flirtations with Rheinmetall. [br]
When firing APFSDS from rifled tubes, the sabot employs rotating driving bands, so rotational torque is somewhat of a non-issue. Obviously, when firing HESH rounds, they must be spun, incurring all the associated problems with which we are so familiar.

 

[Grimstod]

What about placing tungsten in the nose of the bullet like in GS hollow point then close the point with a pointing die. Wouldn't the weight up front improve stability and thus allow for a slower twist because center of gravity would be farther forward?
One more hurdle with the monolithic bullets is the drive bands. What if you had a barrel with rather shallow lands. Would that allow you to shoot monolithic bullets like the GS without drive bands to improve BC? They would not have to cut so deeply into the bullet but since the bullet is stiffer they would still grab it hard and spin it.

 

[Lapua40X]

... At what point does increased mass and slower velocity actually hurt performance?

When the mass is so great and the velocity so low that what the bullet simply falls out of the muzzle.

 

[Catfur]

What about placing tungsten in the nose of the bullet like in GS hollow point then close the point with a pointing die. Wouldn't the weight up front improve stability and thus allow for a slower twist because center of gravity would be farther forward?
One more hurdle with the monolithic bullets is the drive bands. What if you had a barrel with rather shallow lands. Would that allow you to shoot monolithic bullets like the GS without drive bands to improve BC? They would not have to cut so deeply into the bullet but since the bullet is stiffer they would still grab it hard and spin it.

Weight in the nose is the worst place for stability. Weight in the back improves stability, weight on the outer edge increases stability.

 

[mikecr]

How would nose heavy hurt stability?
I would think that with nose heavy combined with hollow base, we could eliminate rifling all together.

 

[Grimstod]

A hallow base would not work. It would get crushed by the powder pushing it.