I wanted to mount a TRS 25 on my wife's AR. Does anyone know what height of a risor would get me an absolute co-exist with a mil-spec height frony sight? Thanks for any help.

UTG RS08S3 "medium profile" is perfect for absolute co-witness, and under $10 off Amazon. Package says .083" saddle height

+1

OK. Thanks, I will give it a try.

Bushnell also make an AR15 version of the TRS-25.  It comes with a 1/3 co-witness which I actually prefer over absolute.  May be worth a look.

Beware.  There is a separate thread here regarding a recent change in manufacturing of the TRS-25.  Bushnell for unknown reasons moved the diode emitter from the four o'clock position to six o'clock.  In doing so, the dot now disappears if moved off center in the upper half of the eyepiece.  This limits the usefulness of a red dot as a parallax free optic or the ability to take hurried shots that may not have time to center the dot.  I have the older 4 o'clock version.  The dot remains visible all the way to the edge of the field of view in all directions. Some are still on the store shelves.  This appears to be an intentional change and not a "bad"  manufacturing run.  Users here report no sympathy from Bushnell regarding this design defect, which seems to be unique to Bushnell.  No other reputable red dot manufacturer has this problem, and Bushnell did not before.  They seem not to care.

I am disappointed at Bushnell, not so much for messing up what was a great little budget red dot, but rather for its stonewalling refusal to recognize that this is a step backward and  fix it.

Yep I got one on sale during xmas for 49.99  and its a 6 oclock emitter and the dot goes away as you move your eye site up.
49.99 dollar paper weight.

I bought two of those scopes during the Black Friday. It's at the 6 o'clock now. With Magpul genII sights there is no problem. With the A2 F mark with flip rear I can't see the sights through the red dot scope.  I'm looking for a different mount for the TRS-25.

You seem to be describing a different issue.  I was referring to the disappearance of the dot when moved into the upper 1/3 of the eyepiece.  This seems to be a trait of all of the newer dots with the 6 o'clock emitter location.  Does yours not do that?  Can you do this below, bring the dot all the way to the top of the eyepiece before it disappears, or does it disappear before you get there?  Apologies for crappy cell cam quality.