got this in on a trade what is it worth? its a large hole slick side preban upper a1 colt.good condition

Just the upper?  or the whole ILLGAL IN CA rifle?
It is the pre-ban LOWER that is valuable.  Without knowing anything else about your rifle (condition is everything) it is hard to place a value on it.

A whole Colt pre-ban 20" rifle in 95% contition is worth perhaps $1400 as long as it is all original.  Others will have various estimates, but when I see someone selling one for $1600 they usually have it for a good long time unless it is some "special model".   I bought a perfectly functional Colt SP1 (colapsible stock, 16" brl)in about 80% condition for a grand last year.  It has parkerizing wear, but is 100% reliable shooter. This appears to have been a bit of a deal, but that was my offer (from an individual, not a gun shop).

its just the upper no bolt carrier or charging handle

Here in Georgia, $200-$250, depending on the condition of the exterior finish.  Bought a complete barrelled upper assy a few months ago, at a gun show, from a dealer, for $325, including bolt,carrier, and charging handle;  all Colt.  99% finish, and throat measured to new spec.