I just bought a pot lead melter to try casting bullets with a dipper.  I had read the dipper method gave better results.  I needed to cast about 200 360 grain 38 55 bullets.  So I cast 120 with the dipper and 120 with my bottom pour melter.  I'm sure many of you are already aware of this but here are the results.

Dipper method:
Mean weight - 360.46
Standard deviation - .531
weight spread - 358.1 to 361.5

Bottom Pour:
mean weight - 361.0
standard deviation  - 2.99
weight spread - 347.5  to 364.5

A big advantage for the dipper method.

I'm at somewhat of a loss as to why this is but I suspect it has to do with the fill rate.  The stream of molten lead coming out of the bottom pour is about 1/4 the size of the stream coming out of the dipper.

B'duckie

Numerous top end competitors have advised me they have better accuracy from bullets that are cast using dippers. 
I have only used dippers to cast even though I have never seen data to verify these claims.

Good to see data that confirms what the old timers have been saying for years.

  When your casting process is under good control, you should see almost all your bullets in ~1 gr. total variation.  

To verify this statement, last night I cast some 470 grain .45 bullets out of 1-40 alloy using a Hoch mold and a dipper.  Alloy temp was 720 degrees.  Once the mold got up to temp I counted to 4 seconds on the pour and left a large sprue.
Weight variation was -.5 to +.5 grain on the 8 or 10 bullets I weighed.  One thing that's important is to keep the dipper spout clean so you get a full stream of melt every time.  I cut off the head of a 3" sheetrock screw and glued it into a wooden handle.  It's a handy tool to ream out the spout.

My experience has been ...... it depends on the bullet.
Heavier, larger caliber bullets - the ladle is superior. 

.22 - .35 caliber the RCBS bottom pour makes just as good (if not better in some instances) bullets as the ladle. That is also true of the lighter weight .44 & .45 Caliber pistol bullets (200-250 gr.).

w44wcf

When I started this game in 1985, I started with a Lee bottom pour, 10 lb pot and have bottom poured ever since. I was competitive from then until 1997 when I hurt my shoulder. 

I've been back shooting, almost 4 years and for the last 2 years, I'm back to being competitive again, still bottom pouring.

I went to the Spokane shoot in May and decided to take 100 Ladel poured bullets and 200 bottom poured. I really couldn't tell the difference. I did shoot back to back 249's with the bottom pour bullets but, all the other scores, you'd be hard pressed to tell the difference. At our local club shoot, I shot a .467 5 shot group at 200 yards and at Modesto last year, my small 100 yard, 5 shot group was .336, with bottom pours.

I bottom pour with the sprue plate against the spout (pressure pour), to get a complete fill out. I like that because it completely fills the base band. My base bands perfectly square and have no rounding on them at all. It just seems "right" to me. Out of 100, I'll get a 2 gr variance. Usually about 3 low and the rest 1.5 gr. I don't cast in order so, I can't tell if the lighter ones are a result of the depth of lead in the pot but, I kinda arrange them in groups of 3 weights. But, 2 gr will go in the same group as the others if they are filled out.

I will run a couple of more tests in the coming year using ladel Vs bottom pour, after all, I am in the minority and if I can find a benefit, I'll switch

Also, I can cast faster bottom pouring than ladel and there is lots less spure lead to throw back in.

Frank

I started out bottom pouring and did so for several years. If the stream of lead is adjusted properly one can achieve the same quality of bullets as ladle pouring. The reason most ladle pourers would disagree is the never put forth the effort with a bottom pour pot to get it right. I went to ladle pouring due to the bottom pour needle valve continually leaking and I am a neat freak when I am casting bullets. I will also mention it was easier to cast quality bullets using the bottom pour and it was at times a frustrating challenge to learn how to ladle pour quality bullets. 

JLouis

Switched from bottom pour to casting with a dipper, and then converted the bottom pour pot to use to make bore laps.

Cast my first at age 7, from a dipper, the lead pot on a friend's mother's kitchen stove.  His grandfather was casting bullets for his Schuetzen rifle and decided grandson & friend should learn how.

Never used a bottom pour pot until the mid-1990s.  A friend had one & thought it was the best way.  We had 2 Lyman single cavity moulds, both with the same number.  Each of us cast 100 from the same pot, same alloy, etc.  My friend used the bottom pour & I used my dipper.  He had about 2 X the # of rejects that I had.  Difference could be technique, or maybe my 1960s mould was better than his 1980s mould.

I have a bottom pour Lee lead pot but do not use the bottom pour feature.