Thought I would chime in with my Glock story and lead bullets. Here is my advice. 1. Slug your barrel and cast /size appropriately. 2. Start at the bottom of the data range and work your way up. 3. If you get accurate results but the bbl shows signs of leading (under 100rds) then powder coat.
I tried shooting lead through my glock factory bbl (glock 34 gen4) and eventually got accurate results. However minimal leading was still appearing, this was before I was powder coating. Tired of the whole thing I bought a storm lake bbl ( which is awesome! ) and I started powdercoating. This solved all my problems. I shot an entire USPSA match (150-170rds) with max load ammo and had no problems with fouling or tumbling/key-holing etc etc. That load for the match was Acc #2 4.5gr under 124gr Lyman 356402. Also a great mold but wish I would have got the 4cav.
I got my lee 6cav to par as well. It is the 124 tumble lube rn design. Now I cast, size, then coat. Why size before coating? My bore needs a .357-358 bullet ( it slugged at .356 ) My lee sizing die .356 actually sizes at .355. BUT this is perfect for me b/c I size all the bullets for uniformity then coat. The coating adds .002-.003 which is just right for the bore. So now this is my go to setup, I havent shot them through the factory barrel but hopefully I will and post results. Here are the results through the storm lake @ 10-12yds off a sandbag. I believe that was a 5rd group. http://gunchannels.com/public/album_...bb7.jpg?c=883d