The Dreaded Double Shifting RD....
 

I'm having the dreaded double shifting issue with my road bike at the low end of the cassette while in the 50t in the front. My cassette goes 11-12-13-15-17-19-21-23-25-28. I'm running an Ultegra long cage RD with a 105 triple FD and a Shimano R-700 crank and a DuraAce chain.

When I'm in the 50 and I'm coming from the 12 to the 13, or 13 to the 14, etc, until I get into the middle of the cassette, I frequently will shift and have nothing happen, then shift again and go up two cogs......once I'm in the middle of my cassette I no longer have this issue.

How do I adjust this ??

The more closely the rear cogs are spaced together the more critical derailleur hanger alignment becomes. That's the first thing that I would check.

+1 although I'd make sure the cable is attached to the derailleur correctly first.

I'd also make sure the cables are moving freely. If they're "gummed up" or otherwise dirty, they could actually be acting "jerky". Pull a bit, nothing happens. Pull a bit more and it "jumps".

Well I'm no mechanic which is why I am posting here but if you had asked me what the the problem was/is I'd have told you a RD adjustment that could probably be taken care of with the barrel adjuster by the RD ? Am I that off track ? The issues are only limited to a couple of upshifts on the low end of the cassette while in the large chainring in front....?

reroute the cable or lube it. it sounds like the cable is not free enough

I'll confess that I assumed you tried the barrel adjustment thing before posting here. I'm going to tell you, however, that misaligned derailleur hangers are common as dirt and the situation that you described is one of the common symptoms.

Quite possible, but you need the right tool to check it. I used to have one, but foolishly sold it along with other framebuilding tools I no longer was using.

+1 on the hanger
also, check that the rear triangle is straight