deleted due to disinterest
But in this case, I was full of crap and you were absolutely right. I might have started out paying attention, but I just looked at the mold as I left it when I completed my session (at about 4:00am in the morning), and it was a mess. Stuff all OVER the mold faces and lead creamed all over the bottom of the sprue plate. Absolutely shameful.Am also hard-core-ruthless in inspecting the cast bullets before bothering to lube or size them...
If there was ever a learning curve, it has to do with casting bullets. Having been there, done that, I hope to never have to recast a bunch of "rejects" again. While I was learning, I have had to scrap entire casting sessions worth of bullets much to my chagrin. Hope things work out for you as you will find that when the bullets come out perfectly, casting is a very enjoyable pastime.. . .You should never cast too fast, for too long, or when you shouldn't be operating heavy machinery or when you should be sleeping instead. Now I have a real mess to clean up, and 1,000 bullets to do over. Serves me right!
Mold diameter tolerance
Our bullet mold tolerance is stated diameter, +.003/-.000 inch. We gauge our bullet molds with a "go/nogo" gauge, which tends to result in bullet molds that run on the high side of the tolerance. You could probably use one of our standard molds at as-cast diameter with good results.
If the bullets are oversize or out of round the mold is not fully closing. A build up of lube, splash of lead, or a burr on the mold block faces are holding them apart. Inspect the mold block faces and carefully remove anything that might hold the mold apart. Make sure to lubricate the locating pins with solid alox/beeswax bullet lube, Lee part number 90007. If these steps are followed the bullets will cast dimensionally correct.
I ran into this problem the other day. was casting some 380's ( lee mold 356-102 1R)I actually deleted the post because I wasn't sure what my point was. Now with a sketch and photo I think I can get the idea across:
Sketch above shows two otherwise identical bullets, but the lower one drops out of the mold a bit larger. Both are sized in the same die. The one that started out fatter gets a longer cylindrical section...that cylindrical section now extending forward of the crimp groove.
The photo below shows one of the worst cases:
This is by far the worst of the lot, most don't show but 1/2 that length of sizing forward of the case. Still, near as I can tell, this is what prevents the cartridge from chambering: I believe the cylindrical section of the bullet is now extending well into the leade, enough that it engages the full rifling.
While these deep-seated bullets do indeed swell the case as you suggested, due to the fact they're seating well down into the case where the wall thickness may be greater (than at the mouth), all bullets are sized the same and therefore even the 'nice' bullets swell the case the same way as the 'bad' bullets do. Therefore, I conclude it's this nasty, brutal sizing on the fatter slugs that's causing the failure-to-chamber problem.
Since I've stopped putting soft lead in my pot and am using only wheel weight lead, I seem to have very few bullets that show sizing forward of the crimp groove, and I'm getting maybe 1% failure to chamber...not good enough, but better. I may have to go up a pound or two on the recoil spring and see if that further reduces the problem.
Does this 'analysis' seem reasonable?