Well, last night I went back to the bottom pour pot. For the single reason that I can sit while casting using a bottom pour.
My dog booby trapped me last night. She loves her antlers for chewing. Like a dummy I walked in-between the couch and the coffee table in a dark room. Took a direct stab from an expertly gnawed and sharpened antler tine. Right at the base of the big toe pad. At least a quarter inch deep. So I'm going to have to be casting while sitting down for a few days. She's a lovely pup. Very concerned at what all the yelling and cussing was about when it happened.
Anyway, the venting mods did help run cooler without band defects. Unfortunately it brought back an issue that I thought I had gotten through a few castings ago. I guess the burr is now on the cavity side and the bullets take a fair bit of persuasion to drop from the mold. This leaves some markings on the driving bands. Not a huge deal, I just need to work that burr free rather than have it in the cavity or in the vent line.
I don't have my cadence down 100% yet, but I found the best success with going back to the method of setting the sprue on a damp cloth... aka a version of BruceB's speed casting method. Found some success in a sequence of 1st pour damp cloth sprue quench, 2nd pour damp cloth sprue quench, 3rd pour wait 3 seconds after sprue color change & open... then repeat sequence. Just need to work on the timing. I can tell when everything is getting too cold based on how hard it is for me to open the sprue plate. I always do this by hand, so I can get a feel for the mold temp.
As for the base defects, these are craters caused by the sprue ripping the lead out, so yes, sprue ripping is a much better term. I was hoping someone had the experience with this kind of defect to take a look at the pic and let me know which to avoid. I can always do a test to see which defects matter, but you know... it's all about saving as many primers as possible. Also, since I do not have a quality load yet, I have to find that first with good bases before I can see what defects impact accuracy. (it annoys me we, as a community, don't use the word precision)
Anyway, the bottom line is, Thank you everyone for your help. I'm not there yet, but there is hope now that I will find the sweet spot and be able to get 100% of the body defect issues sorted out and base reject rate down to about 15-20%. With a 5 cavity mold, I'm more than okay with those results. In all honesty, it takes like 45 minutes to fill an entire quart yogurt container up with these bullets. So with just a few sessions, when everything is firing on all cylinders, I'll have more bullets than I want to use my primer supply on.
Lessons learned: Stick with 2 cav, 3 cav, or steel molds. Those are idiot proof. 4 cavs get tricky, but the sweet spot is found pretty easy. 5 cav molds, the sweet spot is smaller than I care to ever deal with again.