Polygonal rifling and lead bullets?

[Waldog]

I just read on another handloader website that it is not recommended to load/shoot lead cast bullets in pistols with polygonal rifling. Is this a true or is it bunk?

[versifier]

It depends on who you listen to, and what exactly they mean by the term. Some find that Glock barrels lead up a lot, especially in 9mm & .40. But, the way Glock barrels are designed, especially the older ones, you're much better off and safer with an aftermarket unit. I have not heard of anyone complaining about it in .45. At least two other manufacturers make barrels with non-conventional rifling, and have not heard of any problems using lead in them. The grooves are shallow, which means that, like with Microgrooves, the boolit has to be a tight fit for best accuracy.

[Waldog]

I'm not shooting a Glock. I have an H&K USP in .40 S&W that has similar polygonal rifling. I can't imagine that lead wouldn't work but, I thought I would ask other "experts". The only thing I have fired is jacketed bullets in the H&K. I'm at least going to try. I guess time will tell.

[mtngunr]

My understanding is that the polybore can lead badly, depending on gun, alloy, and velocity.....the problems arise when shooting severely leaded bores with already high pressure ammo, combined with some gun designs (aka Glock, and perhaps others?)) featuring large areas of unsupported case-head, which went it lets loose, can really ruin a day and a gun......and perhaps worse....

[9.3X62AL]

I wrote a bit about this subject in the thread "Glock Demystification" a little while back. I actually did some slugging of the bore on my Glock 21 (45 ACP), and found the wide dimension (groove?) to be .453", and the narrower dimension (land? I dunno) to be .449". The throat was .453". I sized boolits to .453" and ran 450 of them--150 of 3 different designs, and 3 powder levels with each design, 50 units per lot, from target to +P pressures. Not one bit of leading, no cleaning throughout the firing sequence, but I did check the bore every 20 rounds or so. So--if a shooter is willing to do all the things necessary to fit boolits to a barrel, the Glock 45 ACP barrel in my experience will produce good performance--and some pretty impressive accuracy, as well. If a shooter just wants to use the over-hardened commercial castings with candlewax paraffin lube--an aftermarket barrel is called for.

The 9mm and 40 S&W aren't lead-friendly pistol calibers in ANY barrel. They run at high pressure, they have insanely fast rifling twist rates, and as mentioned some makes use (or used) unsupported cartridge case head areas in their chambers. Many 9mm barrels are larger than nominal .355" groove diameters, too. The 1911A1 system has unsupported case head areas, and this is addressed in applications where high pressures could cause problems--like 38 Supers run hard to make Major level load intensities. We have seen all these "Glock issues" in other places and on other pistols in the past, but the Glock attracts controversy--so urban legends abound.

In 9mm of any barrel type--slug throat and barrel and size boolits per those results. In 40 S&W, dimensions seem to be pretty good overall--.400" to .401" is the norm, and I have yet to slug one outside those dimensions. The 1-10" twist rate GOTS TO GO.......I bought a CZ-75B with 1-16" twist, and it eats cast boolits like suburb soccer moms on designer chocolate. My own opinion is that the CALIBER and BARREL CHARACTERISTICS are the principal defects in 9mm and 40 S&W when cast boolits are on the menu--and if you are not willing to make the effort to adapt the boolits to these environments, then don't shoot cast boolits in stock barrels.