Here are some photos of the casting session: I know you have seen bullet bases before, but just want to show what I consider to be good bases, the  sprue marks are visible but perfectly smooth
Bases:

a bullet with flashing

The honing stone used to take out the burr. I was reluctant to try it but when you are at the bottom of the well looking up, what difference does it make? I wasnt getting good bullets so I figured I had nothing to loose. Seems to have worked out all right.

Much better but a gas flame should maintain an accurate temp. Do you let it stabilize after the lead has melted? 775 should be a good temp. I preheat my moulds on a cheap (like $13) Walmart hotplate set to medium. I start them before I melt the lead being careful to have the mould basess fully in contact with the plate. Have you tried using 2 moulds in succession (fill 1, set aside, drop 2, refill 2, drop 1, refill 1 and so on)? This helps to maintain an even temp on the moulds and guarantees the sprue is set evenly hard. Once you have the rhythm it goes quickly since there is no time wasted waiting for the sprue to set. I would be suspicious of that lead showing in the far end of the mould joint line. That area should be just as tight as the joint near the mould hinge.

Joe,
Half a grain would be a good place to start when sorting bullets.  Two things that I have learned about getting weights consistent is to use a small fan to cool the mould and the second is invest in a pair of the locking handles that BACO sells.  The last batch of bullets I cast were 2-2-96 alloy at 740 degrees and out of 37 I had cast 32 were +/- .15 of a grain, my best yet.  The other 5 were 3 tenths more because I let the mould get hotter.

Cheers,
Steve

I have found, and this just me, that the final weight of the bullets depends on the amount of lead in the dipper. If I am consistently getting exactly the same amount of lead in the dipper then the bullets tend to be very closely matched in weight. I'm not that good at estimating the volume of lead in the dipper or ladle so I picked up a used RCBS older model promelt melting pot. I have one I use for pistol bullets but thought maybe I could get closer to matching weights if I could control the volume/weight of the lead going into the mold. It seems to work for me but took some careful messing with the flow rates to get consistent results. I have cast bullets for more than 50 years with ladles/dippers and this is now the best matches I have achieved for large caliber bullets cast using pure lead and pure tin.

Todays update:
I casted (any English majors out there, not sure if that is the correct word or is it "cast"?) some bullets today, alternated between a 250 gr mold and the 315 mold, both from Accurate Molds.
Lead Temp= 780-800
Mold temp=  300
Hot plate set at Medium
Help the ladle to the mold for a count of 5 ( which is less that what I was doing before)
Overall, quality was very good. Only had to remelt 4 bullets. Total cast was 95, less 4 rejects, 19 for practice and 72 match keepers. 
I got some flashing when the mold got up to 325 deg, had to lower the temp on the hot plate. 
I did not get as many bullets this trip because I took a lot of time to inspect periodically, so I could adjust mold or lead temp as needed. Bullets from each mold were all within one grain weight ( with two exceptions), which is about as good as I am going to get. 
Based on these results, I think this technique is meeting my requirements. The proof is on the paper, of course, and that depends on the nut behind the stock, the wind and to some extend the orientation of the moon and planets. 
Using two molds has been my habit for many years, not sure how much of a difference it made but it did not hurt, and may have helped keep the mold temp steady. 
Adjusting the temp. of the lead and  mold and reducing the time of contact with the mold and ladle were key improvements which were suggested in your replies, THANK YOU VERY MUCH!
If I make any more "discoveries" I will post them. 

Thanks!
Joe S