Hi, Protoolman,
I have both heard, and heard of, the type of ammo being brought up in court. It all depends on how bad someone wants to get you. DAs don't need to be gun experts, they have all the resources of the police firearms experts at their call.
Some of these guys barely know which end the bullet comes out, but most are pretty sharp, and they work for the state, so they will testify the way the DA wants them to. They usually won't lie, but they will "slant" and "spin" to get the effect the DA wants.
In a case where the bullets that killed a man were never found, the state expert testified that, "The wounds in the victim are not inconsistent with those which would be made by the gun found in the defendant's home." If a jury wants to read that as "expert" testimony that the defendant's gun was used in the killing, it's OK by the expert. If the defense attorney chooses not to challenge such a silly statement, his client is that much closer to jail time.
In that case, the defense counsel did not "cross" the expert and his client got 20 years. (IMHO, he was guilty as sin, but the "expert" testimony was still gibberish.)
Jim