Can anyone explain the difference in the older flat face HK Bolt head, without the contoured face, the Action 3 Bolt Head, and the F Bolt Head? This is in reference to the MP5/5K/SP 89 platforms. Does the different Bolt Heads have to do with what type of loads can be fired, or improved extraction, or something else all together. I have a German HK SP 89, that has the older orig. Bolt Head, and I have a brand new never used, Action 3 Bolt Head, bought here on HK Pro, but I do not know if would see improvments in some area by using the Action 3 BH, or if I swithched , could I use +P or other loads in the gun, without worrying about damage or excessive wear, were I to switch. I do have a problem with weak extractions on the 89. I use mostly UMC 115 gr. Walmart ammo. Any info on the different BH's would be helpful. Thanks.