I am just throwing out some thoughts on the subject. Really it's pure conjecture and I am really very excited about the Scientific results and conclusions that we have derived.

We just may have revolutionized and changed industry standards since 1905"; "making the flat base bullet obsolete"; or at least questioning it. We (NwCP) are at the forefront of revolutionizing the handgun bullet. "sub-sonic velocities", that's were most handguns are and operate (below the speed of sound). Please note the turbulence from "cursory fluid dynamics analysis" photos and note the lack of turbulence behind the bullet of the RBT as opposed to the drag caused by the flat base bullet.

Science has now proven that the base of the bullet is MORE important than the nose of the bullet at handgun velocities. This is what allows the increased penetration and accuracy.

Now I have "Scientific" proof!!!

Here are the NwCP Boat-tail measured BC's and related data and cursory fluid dynamics analysis photos.

All projectiles measured at a velocity range of 925-800fps. Testing was done through a tandem six screen chronograph (Slide 1) at ranges of 3 to 100 yards. The deceleration data and resulting drag data was checked by placing onion skin paper on the chronograph frames. By comparing bore line with actual bullet drop, the drag function could be checked. The test firearm is a Thompson Contender, in .45 Colt, barrel clamped to a rigid bench. Trigger actuation was remote hydraulic and all loads were with Blue Dot powder, Starline cases and Federal Large Pistol primers. NwCP projectiles were compared to the Hornady 300 grain XTP, Hornady 300 grain SST, and Speer 260 grain JHP. These bullets were selected because they represent some of the best bullets in their class. Some bullets tested were excluded from test results, because of lack of quality or lack of specific gravity..

A second experiment was conducted to determine the depth of penetration in water. This test was conducted by simply firing the various projectiles into an twelve foot water trough (Slide 2) and measuring the distance traveled.

Results:
Temp 48°F
Elevation 2500 ft
Barometric Pressure 30.00

Table 1

^a The ballistic coefficients provided by Speer and Hornady are not necessarily “G1”.

^bThese are normalized impact velocities.

^cThe Hornady XTP did expand a small amount at this impact velocity, decreasing its penetration.

Note: NwCP 260 grain vs Hornady SST 300 grain inches of penetration in water.

Note: NwCP 260 grain B.C. vs Hornady 300 grain XTP B.C.

Conclusions:

The lower drag observed with the NwCP RBBT bullets provides for a higher ballistic coefficient and less measured drop as compared to more traditional handgun bullets. In some cases these differences are large (Table 1). The .45 caliber 300 grain NwCP RBBT G1 coefficient is 25+% higher than the .45 caliber Hornady XTP and 6% higher than the Hornady SST. The 260 grain NwCP RBBT G1 coefficient is 13% higher than the Speer 260 grain JHP. In addition, these bullets provide this ballistic advantage without the need for a sharp bullet point, which would limit their use in tubular magazines.

Along the same lines as the air-drag measurements, the water penetration measurements further display the streamline nature of the rebated boat tail design at handgun velocities. The .45 caliber 300 grain NwCP RBBT penetrated an incredible 92 inches of water at an impact velocity of 1000 fps. This is a full 12 inches (13%) further than the pointed Hornady SST at the same impact velocity. It should be noted here that the Hornady XTP did begin expansion at these velocities and this did likely limit its penetration. The 260 grain NwCP RBBT also performed exceptionally well with a penetration of nearly 79 inches; a full 36% further than the Speer 260 grain.

To further explain the mechanics of these observations, we have provided a cursory fluid dynamics analysis of three of the bullet forms at a simulated 1000 fps velocity. Slide 3 shows a comparison streamline plot of the Hornady 300 grain XTP (plot a), Hornady 300 grain SST (plot b), and the NwCP 300 grain RBBT (plot c). Upon visual inspection of the three plots, one can make two important observations. First of all, one can see the reduced turbulence at the base of the NwCP RBBT design compared to the other two bullets. Second, it is apparent that at these velocities, the nose profile makes little difference.

Table 2

Calculated drag coefficients, from the fluid dynamics analysis, match with the experimental G1 values (Table 2). The NwCP RBBT design is predicted by the fluid dynamics analysis to have a drag roughly 4% better than the pointed Hornady SST design at these velocities. The experimental value was determined to be 5%. The NwCP RBBT design is predicted to have a 40% advantage over the Hornady XTP of the same weight by the fluid dynamics analysis. The experimental G1 difference was determined to be 25%. This may seem like a discrepancy; however one must remember that the experimental values are G1 ballistic coefficients that do not model the behavior of the XTP design very well. This is an important note, because it further supports the use of fluid dynamics over arbitrary ballistic coefficients.

The moral of this story is: at sub-sonic velocities the handgun bullets' base has a great deal more importance than the nose of the bullet in reference to accuracy, B.C. and penetration, PERIOD!!!!!!

The most important thing to remember about a bullet base or any flat surface is the bigger the base, the bigger the vortex it will create. An example of this is: lay two sheets of plywood on top of each other, then try and pick up the top one with out picking up the bottom. It takes a lot of effort and eventually the bottom one breaks free. Now do the same thing with the plywood sheet turned on its edge; they separate easily. This same theory applies to the base of a bullet. The bigger it is, the more it tries to pull everything with it. The smaller the base is, the better it goes through things. This is why my little football bullet works so well!

© Copyright 2008 Robert R Sauter (NwCP)

All rights reserved,including the right to reproduce this article or any part thereof in any form or by any means,electronic or mechanical,including photo-copying,recording, or by any information storage and retrieval system, without permission in writing from NwCP..

Thanks,
Robert R. Sauter (AKA Bullet Bob...)
406-723-8683 (anytime)

Specialty Projectiles for Small Arms
Custom Produced by:
Northwest Custom Projectile
Robert R. Sauter (AKA BULLET BOB)
P.O. Box 127
Butte,Montana 59703
406-723-8683
http://www.customprojectile.com

Independent testing was done by: 
Buchanan Ammunition Company, Inc.
1535B Crockett Ridge
Coeburn, VA 24230
(276)-395-3975 TEL
http://www.buckammo.com 

Fluid Dynamics Analysis
DSB Scientific Consulting
616 Finch Ct., Lugoff, SC 29078 
(803)-408-2729 TEL
© DSB Scientific Consulting 2008

© Copyright 2008 Robert R Sauter Permission has been granted to GunLoads.com for display of this article.