Quote:
"Poly bores require lead sized differently than conventionally rifled bores.
A poly bore actually compresses the bullet and rotates it about an axis where as a conventional bore only causes the bullet to rotate around an axis. Due to this, this is why jacketed bullets are recommended in poly bores, from Glock, H&K, et al.
The first step in running lead in any poly bore is to slug the barrel. I bet you'll find that lead should be sized one or two thousands over conventional deminsions for the bore. Most 9mm lead is .356", a Glock needs .358", generally. An undersize bullet will lead to leading, all the time, every time.
Also, hard cast isn't always better. Upon firing, the bullet "expands" from the pressure to seal the bore. In a low pressure round, like .45 ACP, a 11 BHN will expand sufficiently. In 9mm though, something harder, maybe in the 15-22 BHN range, is needed to seal the bore under the higher pressure. Have an improperly hardened bullet, you will experience leading, since it won't seal the bore and lead to gas cutting.
Don't forget twist and bore profile (hex vs. oct) either. 9mm and .40 are naturally less friendly because of more agressive rifling and hex bore profile, compared to .45 and will require a bit more due diligence.
Lube also plays a part. Lar's Red works well in most pistol applications and most rifle applications. Any good commericial lube should do, ALOX, LLA, Lar's, SPG, et al, or home made lube (Felix)."
Source:
http://www.glockpost.com/forums/showthread.php?t=118