For those in a hurry, here's the bottom line: Tested Buffalo Bore Gold Dot and Hard Cast - the two highest energy cartridges available in 380. The Gold Dot penetrated much more than the Hard Cast, and mushroomed uniformly to an impressive .585 inches.
 
Description: Compare Buffalo Bore ammunition from 2 types of carry : 40 caliber from a Kahr PM40 (at 470 ft-lbs energy) and 380 from a P3AT (at 236 ft-lbs energy). Measure penetration depth and maximum bullet diameter. Fire 3 rounds of 40 cal Buffalo Bore type 23A/20 155gr Gold Dot bullet. Fire 2 rounds of 380 Buffalo Bore 100gr hard cast. Fire 2 rounds of 380 Buffalo Bore 90gr Gold Dot.  
 
Target layering: (distance - 15 ft from muzzle)
1 layer denim pant leg  
pork spare ribs, meat side out, room temp, fresh from market
2 boxes of sheet rock plaster - 33lb/box "lightweight" type
 - 9.8 inches of pre-mixed plaster + 0.2 inches of cardboard each
 - 19.6 inches of plaster total
 
Results:
All rounds easily broke through the pork ribs. All shots hit bone. All 40 cal and 2 380 passed completely through the first 9.8 inch box of plaster into the 2nd box. All of these were of the Gold Dot bullet design. 1 of the hard cast 380 did not make it through the first plaster box, a fragment of the other hard cast did.
Penetration: 40 cal = 17.8", 17.1", 16.4";    380 cal = 13.8", the other 3 bullets were not recovered.
 
Observations:
The male sternum (breast bone) ranges in thickness from 1/4 to 1/2 inch, and contains a spongy marrow filled center. Pork spare ribs match this design in thickness variation and content, so should be a suitable target for replicating a shot against a BG. Plaster, on the other hand is anybody's guess as to how good a simulant it might be. It is dense, inexpensive, available to everyone, and easy to shoot (large area, no leakage). However, a followup test with ballistic gel would provide more accurate results.
 
I had no trouble finding the three 40 cal and one 380 bullet by feel. I have no idea why I could not find the other 380 Gold Dot, but it clearly went into the 2nd plaster box in an expanded state as evidenced by the appearance of the holes in the 2nd box. I suspect that the hard cast broke apart. Performance of the 1 380 Buffalo Bore that was recovered was much better than I expected. The 380 penetrated 20% less than the 40 caliber, but did penetrate an incredible 13.8 inches of plaster - after passing through denim, meat, ribs, and 3 layers of cardboard.  
 
Calculations:
Computing the damage volume as recovered bullet area times penetration depth gives 5.73 cubic inches to the 40 caliber and 3.71 cubic inches to the 380 - a 35% difference. The energy difference between these 2 rounds is 50%, so damage volume isn't quite the whole story - but does account for most of the energy dissipation. My guess is that the remaining 15% energy difference between the 40 cal and 380 cal was eaten up by a larger "temporary cavity" volume surrounding the 40 cal bullet's path. The effects of this shock wave area can be seen on the back of the 40 cal 2nd plaster block where 1 of the bullets' shock wave was sufficiently powerful to break out a bit of the cardboard, even though the bullet itself was 1.8 inches away from the cardboard when it stopped.
 
Conclusions:

• Bullet energy determines would path volume - bigger is better. Bullet design determines wound path diameter, and reliability of expansion, at a given velocity against a given target. Looks like BB has found a good balance of these 2 competing forces with the Gold Dot, against a BG target - for the P3AT.
  
• The P3AT with BB Gold Dot is a formidable defensive weapon - penetrating almost 14 inches of plaster with a half inch+ diameter wound path after going through denim and rib cage. Compare the P3AT with BB Gold Dot at 236 ftlb actual measured energy with a S&W SnubNose 38cal +P Double Tap Gold Dot at actual measured 199 ftlb. I'll take the P3AT any day.
  
• Buffalo bore with the Gold Dot bullet is now my only carry ammo in 380, 357, and 40  
  
• Some day, I'll repeat this using 380 only - replacing hard cast with BB flat nose FMJ - using my precious Vyse gel.
  

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dude, if it works in your gun and you like it, go with it.
 
a big +1 there
 
 

Nasty exit holes for the 380.  Thanks for the test results.  

just ordered my Buffalo Bore Gold Dot's  

Thanks for the tests! I always wondered how a P3-AT would do against bone.
 
I feel even more confident now!
 
Bobo

DAMB! You shot up the ribs! Remember, "friends don't let friends shoot up the BBQ dinner."

To help show why I believe that the 2nd 380 gold dot performed well, even though I could not find the @#$% bullet, here is a magnified view of the section between the first and second boxes. Notice the big holes created by the lost Gold Dot round as it passed out of the first plaster box on the right, and into the second box on the left....

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Porky will NOT be happy about this! But it is a very interesting test .. Thanks!