Okay, thanks guys for clarifying. I bought the KKM barrels primarily because I wanted to run lead rounds through them, and I've ssen too many people report problems with firing unjacketed rouds through the polygonal stock barrels to even think about taking a chance. I never had a single jam with my stock 4.6" Glock barrel in it brief use in my gun. I've never had a single jam wit my 4.6" or 6.0" KKM barrels. So, one can tell me that the KKM's are a wast eof money, which subjectively could be true--amatter of opinion. But, both of my KKMs (combined with 22l tunsten spring rod) have never jammed.. They, at least in my hands, produce tighter groups--at least with the ammo I shoot. Not a scientific study to be sure. Alos, the main point of my question above is that don't the KKMs wrap the base of the cartridge a lot better than the stock barrels. I haven't taken pics, but it seems so for me when I compared, and I've seen similar pics from others. That's what I was thinkin gof, rather than a thicker barrel or chamber or superior metal. If either of my two KKMs had ever jammed once, I would worry that they are too tight. But since not, isn't it better to have more support around the base of the cartridge when you're getting up to high-10mm pressures? Or is that not material? I honestly can't say about the materiality of the lesser support. But two KKMs in my gun have never had a single FTF or FTE. So, I'm not worried about the tollerances being too high. Just wondering whether the additional clamping around the base of the cartridge might help prevent the base of the cartridge from rupturing and making the parts below that go "boom."