How does the BC compare to a similar length bullet?

I think “similar length bullets†is pretty much a misnomer, if we confine the discussion to 45 caliber. We are already discussing bullets so long that they can’t even be made of lead, because they would be too heavy. Such bullets don’t look too much like bullets, but are beginning to look more like darts. Darts aren’t spin-stabilized, but are fin-stabilized.

A finless flying body can be constructed by using a wasp-waist: a heavy, solid front section drags along behind it a lighter aft section which also creates drag. The drag from this aft section exerts a constant pull on the front section during flight. This pull acts to rotate the entire projectile around its CG, but only acts if the projectile attempts to depart from its trajectory relative to the still air. If you aren’t a sailor, look up “sea anchorâ€.

So how does the BC compare to the non-turned down version of the bullet? If you're getting a custom barrel you can always get a twist to stabilize the bullet, right?

I don’t know whether wasp-waste OVERKILL bullets will be superior to OVERKILL bullets. But I hope Rob will soon give us a preliminary report.

I do find it interesting that no one has already jumped into this discussion citing previous work along these lines.

Well, I've got the machine time down to 1.5 minutes/bullet. That will bring the cost down considerably. Perhaps to a reasonable range. Hopefully I'll get to fire it this week.-Rob

Rob, will you try a modified program to generate a wasp-waist version? I doubt that this would add any production time per bullet to the eventual costs.

To be honest, I dont see the advantage of the wasp waist design. I'll stick to what Ive already done.-Rob

“Dart Stabilizationâ€

This is to illustrate my understanding of dart stabilization of long, thin bullets, as opposed to the more conventional “spin stabilizationâ€.

Note the figure shows a long thin rod-like bullet which has managed to get itself turned at an angle relative to its direction of travel. Here the direction of travel is opposite to the direction of apparent wind. In addition to the frontal drag, there are two other forces now at work on this rod. These are labeled Fore Force and Aft Force: the Fore Force is applied FORWARD of the center of gravity CG, and the Aft Force is applied AFT of the center of gravity. Both forces are due to the surface areas of the rod now exposed to the wind-stream. If the rod is equal-density along its entire length, the GG is basically halfway from either the front or back or the rod: in still air, this rod would balance at its geometric center.

Basically the Fore Force is seen to be equally balanced by the Aft Force. This is because the Fore Force is attempting to rotate the rod in a direction which would INCREASE the angle, while the Aft Force is attempting to rotate the rod in a direction which would DECREASE this angle. The rod cannot be considered to be stabilized, because no matter what the angle, these two forces more of less cancel one another.

Now consider the situation which would exist if the front half of the rod were composed of lead, and the rear half of balsa. The CG would now be moved well forward of the geometric center of the rod. The Fore Force is now reduced, because the surface area forward of the CG is reduced, while the Aft Force is increased for the opposite reason. And now these two forces are not balanced at all. The Fore Force is still trying to increase the angle, but is greatly overcome by the Aft Force, which is attempting to reduce the angle. This rod is now stabilized.

quote:

To be honest, I dont see the advantage of the wasp waist design.

Rob, I’m a 65 year-old retired Physicist, and in my opinion your OVERKILL bullets are hardly dart-stabilized AT ALL. By increasing twist rate you are attempting to overcome this deficit with spin stabilization.

I see a couple of potential problems firing very heavy bullets at high spin rates. The worst one is the possibility that the bullets will become jammed in the barrel by the high-twist rifling and lead to extreme over-pressurization. Think about it this way: at SOME high twist they will CERTAINLY jam. Say, for instance, the twist was 1 revolution in ¼ inch. This is like a worm gear run backwards. It just won’t work. So how high a twist rate is safe? I really don’t know. But at SOME point, they will just sit there, and not move at all.

Add to this the fact that these bullets are already VERY HEAVY, and just by their very inertia are inclined not to move.

It is a free country, and my advice can be taken or not. But please be careful. I like you, and want you to be around a while longer.

Henry

Keep up the good work, Rob, glad to see some faster twists!

You are only talking about 1:7" twist IIRC?
That twist rate is used with ~2.5" long .338 VLD bullets like the GSC SP .338/295-grainer IIRC.

Some of those barrels are gain twist, I don't have the specifics but could start at 1:14" at the breech and exit the muzzle at 1:7"twist. Some are constant twist 1:7" all the way.

And remember the artillery experiments where a 1:15" twist was compared to a 1:7.5" twist, and caused about one-half of one percent changes in velocity and pressure?

A wasp waist with more mass in the forward section than the rear section would add to dart stabilization. How is that not worth giving a try?

quote:

doubt that this would add any production time per bullet

Er..? Yeah it will...

Tough enough making long bullets on a single end lathe already.

How about production on a multi-axis CNC screw machine with long bar-stock fed from one side, and the last operation being to part off the bullet?

Interesting observations, RIP.

Are the 2.5 inch long rifle bullets you mentioned fired at the typical high velocities ? If so, they would be even more likely to “strip the threads†(leave lead in the barrel) than Rob’s ridgeriders. So maybe my concerns are overstated.

They may not follow the “worm gear†analogy I used before. A worm gear actually uses a threaded shaft turning a sprocket gear with a built-in 90 degree shift in rotation axis’s. But when reversal of the action is tried, and the larger sprocket gear attempts to rotate the threaded shaft, stripping of gears usually results. In this analogy the threaded shaft would be lead (or brass, in Rob’s case) and the sprocket would be barrel steel. Any “stripping†of the threads would be to the detriment of the softer threaded shaft, not the harder barrel steel.

As to the cannon tests, I wonder if the barrels were examined after shooting for evidence of lead? Lead would be evidence of stripped rifling marks on the fired rounds: maybe the higher 7.5 twist stripped the outer layer of lead from the canon rounds, and fired them smoothebore.

Henry22LR:

Sheesh man! The 7" twist .338 Lapua Magnum wins 1000-yard matches with monometal copper bullets at top velocity: No lead, no "stripping."

The artillery tests: I doubt lead was involved there either. What is the jacket of a high explosive modern artillery shell made of? Even old cannonballs were iron!

Sheesh man!

RIP, thanks again for your important insights, I admit my knowledge of firearms history is sketchy at best. Same for current knowledge. I knew the 30 caliber rounds were considered to be about the most accurate of rounds at BR matches, but that was about all I knew.

Now, please scan those memory banks for what we are calling “dart stabilized†and for “wasp waist†in particular. Are we just replowing very old fields, here? In my career I have seen the same “invention†rediscovered many times, and I would hate to be later embarrassed by our going on and on over prior knowledge…

Lets see- Yes I'm very familiar with long .338 bullets in 1:7 twist barrels. Remember, I don't just shoot Big Bores and have done my share of 1000yrd shooting with VLD's. I went with a straight 1:7 as thats what I believe will work!
Actually making a wasp waist bullet would not be much of a problem only a little programing time. Maybe, I'll make some for comparison purposes and to see how much weight it will loose. You do realize the bullet will have to be much longer to obtain the same weight. Thats not an advantage. it was hard enough to get to 800grs with a 2.9 inch long design.-Rob

quote:

Originally posted by Henry22LR:
How about production on a multi-axis CNC screw machine with long bar-stock fed from one side, and the last operation being to part off the bullet?

Yep - that would be ideal.

quote:

You do realize the bullet will have to be much longer to obtain the same weight. Thats not an advantage. it was hard enough to get to 800grs with a 2.9 inch long design

Three inches will just about max out my Spanish Mauser magazine, so I couldn’t go any longer. Maybe 98 Mausers, but not mine.

And lower weight would get me closer to my 850 fps target speed, I expect. I’m sticking to the 14 twist in my first build, mainly because of barrel-blank availability and price.

I don’t expect to even get to 850 fps without hotter loads. But I expect to watch my brass for pressure signs, and stay WELL below 46,000 CUP.

Thanks, Rob. I hope we are breaking new ground.

They are already Dart stabilized as I found out the hard way when I dropped one by accident. Can you over stabilize a Dart? Like over Gyroscopic stabilization? faster twist?
Just guessing but wasp waist would probably drop 100gr in weight. It will also be interesting to see what powders do what in this cartridge.-Rob

Rob, I’m writing a little BASIC program to calculate mass (in grains), CG, and surface areas fore and aft of the CG. For mass-density I’ll use grams/cc, which is also “specific gravityâ€. Water is 1.00. Brass, cast-rolled, is 8.4 - 8.7.

The program will be set up to accept a bullet profile. In programming your CNC, do you use inches or centimeters? Do you input your bullet profile from the front or rear of the bullet? I expect you use bullet radius, instead of diameter, vs. length (from either front or back) as the input array. I want to make the input bullet profile array as similar to yours as possible, for compatibility.

Once I debug the program I’ll post it here.

Here is the first “wasp waist†I’m using, mainly to debug the program. I used a 50 cal because it let me work in simple dimensions.

All dimensions are in inches.

I don’t know enough about the 45ACP casing. I need to know how much of the bullet is “seated†within the case?

I used ½ inch in the above sketch, but I expect that’s too long, because it would not leave much room for powder.

Anybody have the proper dimension? Just ignore the fact that my sketch is for 50 caliber….

See Here:

45 ACP

Thanks Mac, but no banana. I don’t show the case dimensions on AmmoGuide, either because I’m not a paid subscriber or because my JAVA is sub-par.

All I need is one number:

The length of that portion of the lead bullet which is shoved into the 45ACP brass case.

No way to know that without measuring the actual bullet you're shoving into the case.

The case is .900" long - figure if you seat your cruise missile to the sane depth as a factory 230 grain whatever - you'll have about a 8 - 10 grain charge depending on the powder.

.500" seating depthe may be a bit much...

Yeah, I want the minimum seating depth I can get away with to move the CG as far forward as possible. Something tells me 1/8 inch seating depth would be too short. Could I get away with maybe ¼ inch seating depth?

Sure but the case is gonna be along for the ride unless you put some crimping groove in the ass of your ICBM.

You might want to order a box of 45 brass from Midway or just head to the local indoor range and get a handful.

Probably Rob is the only one who can estimate the minimum required seating depth. These “ridgeriders†only get torqued-up to his 1/7 twist RPM by the engagement with the rifling along the length of the seating depth. So the torque gets supplied to the heavy front of the bullet only through the narrow (about ¼ inch) diameter shaft which is the wasp-waist.

Also it would probably be catastrophic if the front of the bullet got “twisted off†the back of the bullet by torsion failure of the brass in the wasp-waist region.

It's all sounding kinda tricky but I'd lke to see more when it's ready.

I went to the Hornady site, and they didn’t spec seating depth for their 45 cal bullets either. But it did look, based on photos they showed, that this dimension increases with bullet weight. So I scaled from their photos of their 230 grain 45 cal bullet. Their 230 grain 45 cal bullets sit 0.322 inches into the brass case, based on this crude measurement.

I corrected my sketch accordingly.

A finished wasp-waist OVERKILL 45 cal bullet would thus be about 2.90 inches overall length, so would fit into my small-ring Mauser magazine just fine.

Current bullets seat 0.470 deep, but thats easily modified. a .45acp case has .7227 inner depth. You wont need alot of case capacity to get these things up to 850fps or so. I will model something that gets as close to the speed of sound as possible.I am going to do some quick load modelling to figure out what powder is best. Remember, you need enough bullet supported in the case for ridgidity in feeding. Since the cases also show some taper, I have added a similar taper to the base of the bullet. I would definately not make the central portion of the bullet too thin and 1/4 inch seems way too thin to me. I too worry that brass that thin could shear under the rotational forces and wind up with a barrel obstruction. BTW I ususally use diameter mode for all my programming.
Addendum- Looks like assuming a 45KPSI safe level in a Rem 700 or equivalent bolt action, that you can push a 800gr bullet to 700fps with Aliant 2400 with about 7.5 grs of powder in a 20 inch barrel with 99% burn. It has about 900ft-lbs of muzzel energy. Also have to reduce the seating depth to .400 inches. To go faster I'll have to reduce the weight. I need to see where I get maximal ME vs weight vs ridgidity all the while staying subsonic.-Rob

Thanks, Rob. I guess for now I can stay with the first sketch, and use it to debug my program. It will be changed all over the place later, anyway. I’ll leave the ½ inch seating depth, and go from there.

As for a too-narrow waist “wringng off†during firing, I can probably calculate the maximum torque it will see during firing. Then I can build a shaft of that diameter, clamp it in a vise, and apply said torque with a wrench. If my test-shaft shows any indication of “taking on†a permanent “set†by not returning to zero when the torque is released, I’d sure not want to shoot such a thin-waist bullet in my gun.

Ok- Just finished my quickload session and a empirical evaluation. Looks to me like optimal will be 700gr bullet, Alliant 2400 powder, Assume 45KPSI working pressure. Bullet needs to seat .330 into the case and about 10 gr of 2400 should make 850fps and over 1000ft-lbs of ME out of a 20 inch barrel. I cant seem to find a better combo without going to higher working pressures. With that said a Rem700 or a TC Encore is fine to 65KPSI and once this design is demonstrated to work, I think thats the way to get closer to the speed of sound.-Rob
I think that taking 100 gr out of the current design will be easy if I take it from the mid section of the bullet. Your wasp waist design makes more sense to me now. However, with a 2.9 inch bullet I don't need to remove all that much material from the waist and thus should not compromise integrity. The shiorter the bullet the worse the problem becomes.-Rob

Looks to me like optimal will be 700gr bullet, Alliant 2400 powder, Assume 45KPSI working pressure. Bullet needs to seat .330 into the case and about 10 gr of 2400 should make 850fps and over 1000ft-lbs of ME out of a 20 inch barrel.

Thanks for running my small-ring Mauser load, Rob. Does Quickload give anything I can use to predict bullet spin in the barrel? Maybe a velocity vs. time or pressure vs. time while the bullet is still in the barrel? Varmit Al has a graph, but only for 22LR. I need it to get a handle on bullet torque for the reasons we discussed earlier.

Adjusting the material spec will allow you some flexibility in the waist diameter and length.

Yes, depending on the alloy chosen, I think it will be easy to complete a design that will balance length, weight and accuracy.
I just got back from test firing my encore with a 1:14 twist .45acp barrel 16 inches long with the 800gr borerider shown in the pics with 8gr of 2400. Fired only 2 rounds.Quick load predicts 29KPSI. It went bang twice and hit a tree stump pretty darn hard. Hole was straight and penetration was impressive compared to a .45 acp. Second shot right next to the first. Probed it with a cleaning rod and at least 20 inches of hard oak. I only made 5 of these bullets so more testing to come. Cases looked fine. There was noticably more recoil than with a .45acp but muzzel blast was about the same( not much). Range was only about 35yrds so much more testing with more bullets at longer range will be needed.
Yes, Quick load does plot chamber pressure vs barrel length. I can send it to you, but essentially, it drops off rapidly in an exponential decay. Assuming 45KPSI at the start, in the first two inches pressure drops to approx. 13600 psi and is only 181 psi at the 20 inch muzzel. Given the gas volume expansion ratio, I think it will take very little to make this very very quiet. Muzzel blast is about the same as my .45 compressed air rifle( that duplicates .45 acp ballistics. Thats the wonderfull thing about DB. A 3 DB increase ( thats doubling of power) usually can just be detected by the human ear.-Rob

quote:

I can send it to you

Thamks, Rob. I'll PM my wife's address to you. She is on fast cable.

quote:

Originally posted by Henry22LR: Ranb40, your 458 SOCOM AR-15 has a 16.5 inch barrel, right? Did you chrono the velocity? Is it silenced?

Yes it is the SS 16.5 inch. I loaded subsonic cast 535 grain and 405 Remington’s to about 1050 fps. The cast bullets keyholed but the jacketed bullets did ok. Only the full power supersonic loads operate the bolt properly. I made a silencer for it, but since they are not legal to use in WA State, I only use it when I travel to legal states. The silencer makes for more blowback, but does not help enough with reliability. The silencer is 12 inches long, but still noisy, not hearing safe to shoot under weather protection, a bit better out in the open though.

Ranb

DEFEXT A-Z

FUNCTION PBMAIN
10 REM shooting bullet profiles
19 DIM B(2335,5) AS EXT


50 OPEN "COLUMN1.PRN" FOR OUTPUT AS #1
51 OPEN "COLUMN2.PRN" FOR OUTPUT AS #2
52 OPEN "COLUMN3.PRN" FOR OUTPUT AS #3
53 OPEN "COLUMN4.PRN" FOR OUTPUT AS #4
54 OPEN "COLUMN5.PRN" FOR OUTPUT AS #5
55 OPEN "COLUMN6.PRN" FOR OUTPUT AS #6
100 PI=4.0*ATN(1.0)
210 CAL=45.0
220 FOR Y=0.0 TO 0.322 STEP 0.001
230 X=CAL/100.0/2.0
240 I=I+1.0
250 B(I,1)=I:B(I,2)=Y:B(I,3)=X
260 NEXT Y
265 X0=CAL/100.0/2.0
270 FOR Y=0.333 TO 0.555 STEP 0.001
280 Y0=Y:IF X0<(CAL/100.0/4.0) THEN 320
285 X=X0-0.001
287 X0=X
290 I=I+1.0
300 B(I,1)=I:B(I,2)=Y:B(I,3)=X
310 NEXT Y
320 FOR Y=Y0 TO 1.206 STEP 0.001
330 X=CAL/100.0/4.0
340 I=I+1.0:Y0=Y
350 B(I,1)=I:B(I,2)=Y:B(I,3)=X
360 NEXT Y
370 FOR Y=Y0 TO 1.572 STEP 0.001
385 Y0=Y:IF X>(CAL/100.0/2.0) THEN 430
386 X=X0+0.001
387 X0=X
390 I=I+1.0
400 B(I,1)=I:B(I,2)=Y:B(I,3)=X
410 NEXT Y
430 FOR Y=Y0 TO 1.572 STEP 0.001
440 X=CAL/100.0/2.0
450 I=I+1.0
460 B(I,1)=I:B(I,2)=Y:B(I,3)=X
470 NEXT Y
475 REM GOTO 560
480 REM BULLET TIP
500 R=5.0/4.0
510 FOR Y=1.573 TO 2.322 STEP 0.001
520 X0= CAL/100.0/2.0-R
522 Y0=1.572
524 ZTOP=R*R-(Y-Y0)*(Y-Y0):IF ZTOP<0.0 THEN 560
526 X=X0+SQR(ZTOP)
527 IF X<0.0 THEN 560
530 I=I+1.0
540 B(I,1)=I:B(I,2)=Y:B(I,3)=X
550 NEXT Y
560 IMAX=I
600 FOR I=1.0 TO IMAX STEP 1.0
610 WRITE #1,B(I,2):WRITE #2,-B(I,3):WRITE #3,B(I,3)
620 NEXT I

700 REM CALCULATE DISC MASSES THRU LINE 770
710 RHO=8.49
720 FOR I=1.0 TO IMAX STEP 1.0
730 RDIN=B(I,3):RDCM=RDIN*2.54
740 AREA=PI*RDCM*RDCM:MASSGRAMS=AREA*RHO*0.001*2.54
750 MASSGRAINS=MASSGRAMS*15.4323584
760 B(I,4)=MASSGRAINS:WRITE #4,MASSGRAINS
770 NEXT I

800 REM CALCULATE TOTAL BULLET MASS THRU LINE
810 TOTGRAINS=0.0
820 FOR I=1.0 TO IMAX STEP 1.0
830 TOTGRAINS=TOTGRAINS+B(I,4)
840 NEXT I
845 I=IMAX+1.0
850 WRITE #4,TOTGRAINS

8400 CLOSE
8600 EXIT FUNCTION

END FUNCTION

The above BASIC program loads the bullet profile and computes the total mass of the bullet in grains. For mass density of the brass I used 8.49 grams/cc.

Tomorrow I will add center-of-gravity calculations.

I thought I had finished the BASIC program, but as it turns out I had a bug. I think I now have it fixed, and working. The program calculates bullet mass in grains, center of gravity in inches measured from the bottom of the bullet, and dart stability. The program converts the bullet into 0.001 inch-long “discsâ€. The total mass of these discs is the total mass of the bullet. The center of mass CG is calculated by discovering that point at which the bullet would balance if placed on a straight-edge. From that special point (the CG), the sum of each the discs to the left, times their distance from the CG is equal to the sum of each the discs to the right, times their distance from the CG.

Dart stability is computed much like CG, except that instead of using the mass of each disc, the surface area of each disc’s rim is used. Both a “leveraged fore area†and a “leveraged aft area†are calculated. To be dart stabilized, the “leveraged aft area†must exceed the “leveraged fore areaâ€: the more it exceeds it the more dart-stabilized is the bullet.

Looks like “dart stabilization†is not possible with the bullets I have shown previously, because those bullets are too “pointyâ€. The original bullets had a radius of curvature in the bullet point area of 1.25 inches, and this is too much. A smaller radius is called for, more on the order of the OVERKILL bullets which Rob showed in his photographs. Looks like longer bullets are greatly favored as to dart stabilization, as Rob previously suggested.

In a Spanish Mauser, converted to 45ACP firing, the maximum overall bullet length is barely over 3.0 inches. I’m using 0.322 inch seating depth, and 0.9 inch brass case length. Thus about the longest the bullet can protrude from the case is 2.1 inches, and the longest projectile is about 2.422 inches.