1991-A1 rear sight question. How do I know it'll fit, before I buy it?

[gearchecker]

Is there a difference in the dovetial in a Series 70 and a Series 80 1911/1991 pistol.
I have a Colt 1991-A1 Series 80 full size pistol.
I have fixed sights on my pistol currently and I want to change the rear sight out to an adjustable set.
I'm looking for a rear sight that'll drop in without having to machine my slide if at all possible

I've looked around and I've seen a few sets listed and they indicate different dovetial widths.
One lists this: Novak style .495 x 65 degree dovetail
another just states it's a .250 dovetail
and another lists a Standard Bomar .359 X 60 dovetail

All the help I can get is appreciated.

Regards,
Gearchecker

[dfariswheel]

All standard Colt sight dovetails were the same.
I don't think the dovetail changed from 1912 to today. The 1991A1 uses the same dovetail as a WWI or WWII or any commerical .45.

As I recall (Note the qualifier) the standard Colt rear sight dovetail is .250.
Many of the other sizes you're seeing are for Springfield and other brands who use odd sizes, and for Novak. Also notice that often, the sizes given are for FRONT sights that dovetail in.

Brownell's carry just about everything that's worth having, and if you call the Tech Staff, they'll help you select the right size for your Colt.