I believe there were 4 in the arm.
A good 9mm self defense round of 124 or 135gr will expand to .50cal and blow through to the other side.
Sure, .40, .357 and .45 are better.
But 9mm is plenty good if you can hit with it.
The gripe in military combat is ball ammo. Not an issue for us.
And, as always, shotgun and rifle rounds are ALWAYS more effective than pistol.
None of the bullets came out the back so I’m thinking it was 9mm. A .40 would have. IMHO