This isn't exactly about A.P. rounds,But I bought some ammo the other day that had a polymer case. The first part from the rim to about 1/2 " up was brass then the rest of the way to the crimp ( If you want to call it that. can bend bullet out with finger) was gray plastic looking junk.Don't buy any for semi autos They are jam-o-matics. They may be alright for a bolt.I didn't even bring the rest of the 100 home to give them a chance.LOL Just thought ya'll might be interested.BTW I was shooting them in my A.R. and rarely if ever have a problem with feeding or jams it was trying to feed two at a time,bending the bullet and sending another one up under it.Not to good.