1911 45 auto Barrel/Bushing

Which the minimum tolerance is from barrel bushing for best accuracy?

Yes.

Less than 1000th.

Way more to the accuracy equation than barrel/bushing fit.

A proper bushing fit can take a 4 inch RO at 50 Yards and make it 2 inch gun with the stock barrel. 

I test by pulling the slide back a little bit and using a feller gauge to measure the gap between the barrel and the bushing. Most guns will express very little movement in battery. 

Under 2000th is good to go. 

What you do not want is a sprung barrel , meaning the tight bushing is compensating for poor barrel fitting. That is how less Baer makes them now. They are good for about 5,000 to 10,000 rounds and then need to be refitted. 

You can tell if you have a tight bushing and a poor fit if the primer hit is well off center and if there is uneven wear and witness marks inside the bushing.

Barrel springing is when the bushing is not relieved enough to allow full lockup/battery without bushing bind; actually can bend barrel.
Measure the barrel OD and bushing ID separately to see what the fit/clearance is.
A slightly loose bushing can still shoot well because barrel cams into lockup/battery.
Barrel fit is comprised of at the rear of the barrel (upper lugs, lower lugs/slide stop pin; hood not part of our equation right now)  and at the bushing.
Frame to slide fit can affect slide stop to bottom lug.
What happens on one end can affect what is happening on the other.
RO without properly fit barrel (Kart,KKM, etc) is a rock bottom BE pistol;even it if shoots 2” at 50. 
Reader’s Digest version
To answer the original question, if you know what you are doing you can build them darn tight! Less than 0.001”
Jon

I have shot some LBs that felt like an interference fit at the rear of the barrel.

I picked up a brand new LB out of the display case at a local gun shop several years ago.  Neither I nor the gunshop salesman could cycle the gun by hand.  Wedge fit I guess.

I'll also offer that bushing to slide fit matters too. I measure the slide opening with gage pins and then order a custom bushing from EGW that has an OD .001" undersize and an ID .001" oversize. Still requires a small bit of hand fitting but works great for those of us who dont own a lathe.