30" hg is a perfect vacuum and is not possible. I believe the most that can be pulled with a vacuum pump is around 28"hg.
A two stage rotary pump will do better than 28" hg.
Back in the day when guys were using pumps made fro old recip refrig comps
it was common knowledge that because of the clearance pocket for the piston there was always a little bit of air left over. This plus the limiting design of the piston made 30"hg impossible.
Some guys would get an old rotary refrig comp but because the oil was never changed in the comp 30' hg was not possible in this instance either.
And that ok Buddy we all started somewhere unlike some here that will make you feel so bad and belittle folks because they were born with a micron gauge in there butt and a NATE certificate in there hand and a Sling Psychrometer in there teeth. Rather than putting folks down here that haven't used these few tools of the trade we "Pro's" should be encouraging old and new Pro's that haven't been using these tools how these tools can be beneficial to them in servicing a/c equipment. I guess instead of the sarcasm and put downs use our knowledge and experience and treat these folks as students and teach them as any good teacher should, remember none here knows it all anyway, but if we all work "together" we can all gain knowledge from one another, "maybe" even something we did not know, just my two cents.
'two cents' like that spends like a dollar with me. very nice.