Dr. Roberts said:
Other than being able to perforate soft body armor, the 5.7 x 28 mm used in the FN P90, as well as the 4.6 x 30 mm fired from the HK MP7 cause wounds less incapacitating than those made by 9 mm FMJ fired from a pistol.
I have personally fired the 5.7 x 28 mm FN P-90; velocity, penetration, and tissue destruction is like a .17 Hornet--far less than we see with 75 gr TAP or 77 MK out of our M4’s. Winchester RA45T 230 gr JHP’s fired from our duty 1911’s crush more tissue and penetrate further than the 5.7 x 28 mm. Use of the 5.7 x 28 mm is a good way to ensure mission failure.
Several papers have described the incredibly poor terminal performance of projectiles fired by the FN P90.
--Dahlstrom D, Powley K, and Gordon C: “Wound Profile of the FN Cartridge (SS 190) Fired from the FN P90 Submachine Gun". Wound Ballistic Review. 4(3):21-26; Spring 2000.
--Fackler M: "Errors & Omissions", Wound Ballistic Review. 1(1):46; Winter 1991.
--Fackler M: "More on the Bizarre Fabrique National P-90", Wound Ballistic Review. 3(1):44-45; 1997.
--FBI Academy Firearms Training Unit. FBI Handgun Ammunition Tests 1989-1995. Quantico, U.S. Department of Justice--Federal Bureau of Investigation.
--Hayes C: “Personal Defense Weapons—Answer in Search of a Question”, Wound Ballistic Review. 5(1):30-36; Spring 2001.
--Roberts G: “Preliminary Evaluation of the Terminal Performance of the 5.7 x 28 mm 23 Grain FMJ Bullet Fired by the New FN P-90 , Using 10% Ordnance Gelatin as a Tissue Simulant”, AFTE Journal. 30(2):326-329, Spring 1998.
--Roberts G: “Terminal Performance of the 5.7 x 28 mm 31 Grain SS-190 FMJ Bullet Fired by the FN P-90 in 10% Ordnance Gelatin.”, AFTE Journal. In Press.
The early 5.7 x 28 mm 23 gr FMJ bullet fired by the FN P-90 had insufficient penetration for law enforcement and military use. The current 31 gr SS-190 FMJ bullet has nearly adequate penetration, but the wound resulting from this projectile has a relatively small permanent crush cavity, as well as an insignificant temporary stretch cavity. Although the 5.7 x 28 mm penetrates soft body armor, wounding potential is at best like a .22 LR or .22 Magnum. Even 9mm NATO FMJ makes a larger wound--and we are all aware of the awe inspiring incapacitation potential of M882 ball from the M9......
Numerous other projectiles commonly used for law enforcement and military special operations applications, such as a good 9mm, .40 S&W, or .45 ACP JHP, the better 5.56 x 45 mm BTHP/JSP loads, as well as 12 gauge shotgun slugs and 00 buckshot, all provide better penetration, crush more tissue, and have far greater potential to reliably physiologically incapacitate an aggressor than the 5.7 x 28 mm 31 gr SS-190 FMJ bullet fired by the FN P-90. Law enforcement agencies and military special operations units are strongly urged to avoid adoption of this weapon system.
, it is as good as most guns to eliminate any threat. 
5.7 at 9mm prices? I hope so!
