Had the same issue - was shooting a 'classic' Hi Power, it took me a month to get it shooting decently, now it's very very good. I can tell you what I did.
First of all, you must use jacketed bullets with the Glock; don't even try lead. Lead bullets and polygonal rifling don't mix. You're using jacketed bullets already - no problem.
Second, use the caliper to measure the diameter of the case mouth after you crimp; it must be at (or close to) SAAMI spec. The 9mm headspaces on the cartridge mouth, so the diameter must be correct; no less, certainly no more or you'll run into feeding issues. You use a taper crimp for 9mm - roll crimp is a no-no.
Why it's shooting all over the place? Could be several reasons - 9mm is a pain to reload, I recommend you get a gauge block and verify that all your reloaded cartridges fit fully in it - but in my case, I was not pushing the bullets fast enough. I use fast powder - tightwad, which you can't even find 9mm pistol reloading data for; you might try Vihtavuori N310, Bullseye or Red Dot - and what clued me in was that like you, I was shooting foot-and-a-half groups at 20 yds; by 'n by, I realized that the outermost hits were often keyholes. This meant that the bullets weren't spinning fast enough to gyro-stabilize; and the only way to spin them faster (other than installing an expensive custom match barrel with a tighter twist) is to push them faster. In my case, it took literally 0.1 grain more tightwad and the pistol started shooting like a champ.
For a slower powder, you may need more than 0.1gr - WITHIN documented max loads, of course - but try more powder; that may solve your problem. And chrono your loads, so you know what velocities work.
First of all, you must use jacketed bullets with the Glock; don't even try lead. Lead bullets and polygonal rifling don't mix. You're using jacketed bullets already - no problem.
Second, use the caliper to measure the diameter of the case mouth after you crimp; it must be at (or close to) SAAMI spec. The 9mm headspaces on the cartridge mouth, so the diameter must be correct; no less, certainly no more or you'll run into feeding issues. You use a taper crimp for 9mm - roll crimp is a no-no.
Why it's shooting all over the place? Could be several reasons - 9mm is a pain to reload, I recommend you get a gauge block and verify that all your reloaded cartridges fit fully in it - but in my case, I was not pushing the bullets fast enough. I use fast powder - tightwad, which you can't even find 9mm pistol reloading data for; you might try Vihtavuori N310, Bullseye or Red Dot - and what clued me in was that like you, I was shooting foot-and-a-half groups at 20 yds; by 'n by, I realized that the outermost hits were often keyholes. This meant that the bullets weren't spinning fast enough to gyro-stabilize; and the only way to spin them faster (other than installing an expensive custom match barrel with a tighter twist) is to push them faster. In my case, it took literally 0.1 grain more tightwad and the pistol started shooting like a champ.
For a slower powder, you may need more than 0.1gr - WITHIN documented max loads, of course - but try more powder; that may solve your problem. And chrono your loads, so you know what velocities work.
