There is always if i recall correctly either "leementing" the mold or, less perminently, "beagling" the mold. Just be sure to use a soft fat boolit, that will obdurate and prevent gas blow by.Thanks Wills
I fought a long battle with leading in this rifle - got it second hand and there were a couple tiny rust marks near the muzzle from long term storage - I freebored it to get rid of the worst - later bit the bullet and lopped two inches off it and re set the front sight - still was having problems - most of the boolit designs around at that time were cut for smokeless - I must have went through half a dozen molds - bore riders - postel designs - molds for a classic blackpowder rifle with tiny little lube grooves ahhhhhhg! Lube cookie under the boolit helped but the lube disc and two wads took a heap of powder space - was at a shoot in the hills and a feller was there selling gear - had a LEE 459-500- 3R mold - not long after they started listing it - soon as I saw that I grabbed it - finally someone has woke up what this boolit should look like - good big lube grooves and a pointy nose - I had been shooting a 500grain bore rider with a flat nose and hardly any lube aboard - scrubbing my barrel between shots - that LEE boolit took a full hundred yards off my sight setting - I read about the blow tube about the same time - first time I put all this together I got a first at 500yards at our local club's annual shoot - not a score that would rate high with you fellers but I was pleased and no cleaning between shots! So then I start to read all this guru stuff from the US saying that LEE boolit is uesless - wont shoot over 500yards - a whole bunch of negative feedback - whats with that was my question ?? I figured out later that they had a quality control issue on that mold and its likely a bunch of them went out undersized and under weight - I liked the design so much I bought two of those dodgy molds - wrote to LEE about it - they offered replacements no cost - but postage back woulda wiped out most of the benefit - I elected to keep them and salvage the handles out - after they got it fixed I got another two holer and using that now - so - a long road for me but when I finally got the lube problem sorted out - no more leading - I use a blow tube and I do think that is an art - something that looks absurdly simple but isnt