Lead Squib x 2

[Wobbly]

Isn't that what a good quality powder drop is for?

It isn't usually the quality of the measurer that is in question.  It is the consistency of the operator.  Everytime you move that lever up and down, it needs to be done at the same speed, all the way up, all the way down.  The pause at the top needs to be the same each time. 

+1 on steady, unchanging technique.

I have always used a technique I call 'knock-knock'. At both the top and bottom of the throw, when the lever comes to the stop, I knock it twice against the stop. The induced vibration helps the powder in the hopper to become a consistent density, a trait mandatory for accurate use of volumetric measures.

Powder baffles also help.

 

[SMSgt]

I thought the same thing!!!!!
I started measuring bullets they all were 1 grain light or heavy. Mainly lube

My point was to measure the powder, from every drop, before you seat your bullet.

I'm reading that his loaded rounds were within .5 grains, which is perfectly normal with cast bullets. His powder loads were correct--bullet weights varied. In the big picture of reloading, 2 grains varience in bullet weight isn't going to be an issue in a reloaded round, especially as he's concerned about the squibs.

[Wobbly]

I measured the rotor NOT installed. 6.75. The rotor in the RCBS is definitely pistol rotor.

6.75 what ? Inches? That makes no sense. 6.75mm makes no sense. If this is the precision you use to measure things, then you're going to be in big trouble with reloading. Just saying.

I measured each remaining loaded lead round. They were all within 0.5gr of each other - except 3. One was 2.6gr light!!!  Pulled all 3. Each powder was exact - 4.2gr. All three had light boolits - 123gr instead of 125gr.

IMHO no significant data can be had by measuring finished cartridges. The bullets and brass both vary too much.

I am leaning more and more toward distraction regarding squib and lack or powder as the culprit.
Any thoughts?

How about 'operator error' as the culprit, revealing itself through 'lack of powder'. Inanimate objects, like powder, can't just decide which cases it will, and will not, go into.

Having screwed up almost everything I touched for over 60 years, I'm now ranked as an expert on the subject.