There is some ammo sensitivity. Lead bullets leave shavings in the gas port that can quickly choke up a the gun. The operating range it was designed for was 100 to 125-grain bullets at a healthy velocity. The P7 seems to work ok with 147 grain subsonic rounds, however H&K not too long ago mentioned that 147 grains accelerate wear on P7. I will be looking into that issue some more in the future.

+P and +P+ seem to work fine though there is some issue about +P+ in the M13. A few reports have mentioned that +P+ cases can sometimes get stuck in the chamber of the M13 to the point that a rod and hammer is required to remove the stuck case. The odd part of this is that it seems to only happen on the M13 and not the M8. Two of the reports were with Corbon loads and the other there was no mention of what manufacture of the round. The HKP7 site had more info so stop by there.

The best 9mm load that has been mentioned the most is the 127gr +p+ Winchester Ranger Talon (the new LE "Gold Talon" version). Unfortunately, it's not commercially available even though it's not illegal for civilians to purchase (thru gunshows) or possess. And when you do find some, it costs an absolute fortune. It's up to you if you would want to put up to the hassle and the cost to acquire some. But if it's as good as they say then why not.

The 124+p Remington Golden Sabre would be right behind and it is commercially available. Same with the Federal Hydra-Shok and the Hornady XTP.

Triton and Cor-Bon loads are the choice of the fast/light crowd. Be aware that many knowledgeable pistoleros wouldn't touch Cor-Bon ammo because of overpressured loads and quality inconsistencies (which Cor-Bon claims to have fixed). Triton has an excellent reputation for quality. The Mullins 115+p+ GD load may be one of the best of the fast/light lot.

Also, ProLoad has some excellent 9mm offerings, considered by many to be the best commercial ammo available. Another noted load is the Speer 124 grain +P Gold Dot.

For competition use IMI or Samson Brand 124 gr FMJ seems to be great round. Very accurate and consistent, and never a jam according to one shooter.

As with any gun/ammo you should try and fire at least 200 rounds of a chosen load to insure that it will work in your pistol. It can be expensive but you wouldn't want to find out your pistol doesn't like your ammo during a gunfight.