Polygonal rifling is made for Jacketed bullets. You can definitely run into issues using lead rounds (even some of the softer plated rounds aren't ideal).

 

There are a lot of debates on this topic. Some say jacketed only. Some say if you don’t load lead projectiles to high velocities & clean after shooting that you’re ok. I’ve heard that high velocity lead can start skipping the polygonal rifling & lead very badly. Not sure of the velocity needed to do that. It probably depends on bullet composition, hardness, & maybe even powder burn rate/temperature.
This is what HK says :
CAUTION: HK firearms are designed to function with quality, manufactured brass- cased ammunition. Use of steel or aluminum-cased cartridges is not recommended and could adversely affect safe and reliable functioning. Use of cast-lead bullets is also not recommended.

 

Thank you for posting this, I have a new to me P9S and had no idea about the recommendations. So far I have only fired brass ammo through it.

 

My experience with poly barrels and lead projectiles has always been negative severe leading and fouling with increased pressures (assumed) by the large rise in recoil felt. This was on a Steyr GB 9mm which was quite a robust pistol. Recommend against using lead in semi auto pistols. I stick with factory and NATO type loads, YMMV.
regards, PeterNNH

 

I used to shoot lead out of Glocks since long before internet gun forums came into existence. The HK P9S, especially in the Sport version, had been very popular among German top competitors in DSB matches. Since they mostly reloaded and were casting their own boolits, HK officially gave some guidelines. They included general reloading infos and common sense rules, as well as recommendations about bullet weights, alloys, and velocities. In 1991 Gerd Luck had not developed coated swaged bullets for Haendler & Naterman, yet, so coated bullets are not mentioned.

The HK P9S - with lead boolits - won more than one national championship in HK's native Germany. This should debunk some of the internet myths about the inaccuracy and dangerous pressure level generated by lead bullets shot out of a barrel with polygonal rifling.

 

I used to shoot lead out of Glocks since long before internet gun forums came into existence. The HK P9S, especially in the Sport version, had been very popular among German top competitors in DSB matches. Since they mostly reloaded and were casting their own boolits, HK officially gave some guidelines. They included general reloading infos and common sense rules, as well as recommendations about bullet weights, alloys, and velocities. In 1991 Gerd Luck had not developed coated swaged bullets for Haendler & Naterman, yet, so coated bullets are not mentioned.

The HK P9S - with lead boolits - won more than one national championship in HK's native Germany. This should debunk some of the internet myths about the inaccuracy and dangerous pressure level generated by lead bullets shot out of a barrel with polygonal rifling.

This is interesting info. But you are the OP so I'm confused. Did you uncover this info in the last 24 hours or so?

For me, I reload coated lead and have spare barrels designated for the lead. Cheap and easy to do with p2k USPc, etc . Not as easy with P9S

 

No need to be confused. I am following the internet lore of lead bullets in barrels with polygonal rifling for decades and just wanted to see what people's opinions here were. I have shot with professional shooters that tested SIG Sauers, like J. Rehr, and he had successfully shot lead out of polygonal barrels with great results, keeping velocities low and carefully choosing components.
HK obviously has come up with a verdict long ago and that is what I want to share with folks on this forum for nothing else but a consideration, information from the HK Gruppe, not some keyboard jockey on the net.