Yeah, I hear what you are saying about backing off the charge.  But I have a 40 cal already and really don't want to shoot this 10mm with 40 cal type performance.  I will probably just get some decent jacketed bullets for this gun.  Or maybe look into an aftermarket barrel later on.  Anyway, I appreciate this forum and will keep experimenting. 

Hello everyone.  I recently received a Gen 4 Glock 20 for my b-day and have run into an issue (in addition to the slide locking back with 1 round 180 gr Underwood left in the mag which I think I've fixed).  I've shot tons of 165 Xtreme plated out of my Glock 23 with 7 grains of Longshot.  Fairly clean load, plenty accurate and averages about 1050 fps.  So I thought, I'll load up some of these 165's for this 10mm and hope for around 1250-1300 fps.  There is no published load data that I could find for Longshot with 165's in 10mm, so I winged it.  Started at 9.0 gr and worked up from there.  My three groups of test loads averaged 1230, 1260, 1285 respectively.  I don't believe I over-crimped them and according to Xtreme, these bullets should not start falling apart at these velocities, after all, copper plated 22 long rifle bullets hold up fine at 1250 fps.  They all functioned properly with no failures of any kind, but extremely inaccurate!  I could not make two shots hit within a 12 inch circle at 15 yards.  I'm no expert, but I'm not that bad.  Shot some Underwood just to check the gun and they were very accurate.  I don't know whether I want to scrap the plated bullet idea in this gun, or try some 180's with Longshot.  Anyone out there have a bad experience similar to this?