* Below are two opinions on shooting cast bullets in Polygonal barrels (e.g. Glock, HK, etc.). One is from a cast bullet maker, the other from a leading ammo company.
Shooting Cast Bullets in Glocks - by Bob Palermo, President of Penn Bullets
I get a good number of inquires about lead bullets being used in Glocks so I’m going to express my thoughts on the subject. The most common thing heard about Glocks, as well as H&Ks and Kahrs for that matter, is that you should not use cast bullets in these guns due to the polygonal rifling used in these guns. It is said that such rifling causes dangerous pressure spikes in such guns and the result is a dangerous KB (kaboom) destroying the gun and injuring the shooter. This is due in part to the fact that the polygonal rifling impresses the rifling into the bullet rather than engraving the rifling thru the bullet as with conventional lands and grooves. Couple this with any fouling and the over pressure problem becomes even more acute. So my first piece of advice is to NOT DO IT. And I’m not going to be held liable should you not heed that advice and venture forth on your own.
Now having said that, I can tell you that many people load cast bullets in guns like the Glocks and they have shot tens of thousands of bullets thru them with no problems If one were to go to the Glock Forum and the Reload section there are many threads about this very subject. The important thing in making this work is know what you are doing before you start:
(1) Only use quality cast bullets in the intended application.
(2) Get the bullets sized to nominal dimensions rather than the standard .001" diameter that most cast bullets are done at.
(3) Use clean, cooler, slower powders for the application and work the loads up from there.
(4) The gun needs to be clean of any copper or moly fouling.
The gun needs to be checked after the first 5 rounds fired for any signs of fouling from the bullet load combo you are running. If the load is clean then proceed to fire another 5-10 rounds and then check for any signs of fouling along the way. If the load exhibits any signs of excessive fouling then you have to stop, rework the load, clean the gun and start over. Eventually you should be able to work out a load that will permit you to run about 100 - 150 rounds between cleaning. The .40 S&W is the worst culprit due to the fact that the pressure curve is a very peaky one to begin with and the chamber is unsupported in the Glock barrels. HS-6 has served me well in this application.
If all this seems like too much effort then you can always get an after market barrel with conventional rifling and not worry about it. There are a number of quality after market barrel makers that will fulfill this need should you chose to go in that direction.
Shooting cast bullets in polygonal barrels, by Tim Sundles, President of Buffalo Bore Ammo
True hard cast bullets (as opposed to lead
swaged bullets) that are properly lubed will not lead foul polygonal
barrels any more than any other type of rifled barrel. Ever since Glock
Corporation warned to not use lead bullets in their pistols with
polygonal barrels, a myth that hard cast bullets will lead foul
polygonal barrels has become wide spread in some parts of the firearms
world. However, the myth is untrue. Hard cast bullets are not "lead"
Pure lead or nearly pure lead bullets have a tendency to foul any barrel, not just polygonal barrels. Years ago, when several Glock pistols experienced cracked barrels because of fouling build up from shooting pure lead bullets, Glock issued a warning not to shoot lead bullets in their polygonal barrels. From that warning, the myth that you should not shoot hard cast bullets in polygonal barrels was born.
Provided you use real hard cast bullets with good lube, you can shoot them all you like in polygonal barrels without causing lead fouling deposits at the front of your chamber or anywhere else in the barrel. If you are concerned about lead fouling from hard cast bullets, all you have to do is to clean your barrel after firing hard cast bullets and before firing any jacketed bullets. However, in my experience, quality hard cast bullets won't foul a Glock polygonal barrel or any other type of barrel but lead bullets normally will.