The TR21R (red is the one most 3-gunners use), is an excellent scope for that application.  I have shot one quite a bot (we sell them as well), and sponsor Taran Butler, who used one almost exclusively this season in 3-Gun matches.  (He shoots our competition uppers too).

The trick is to get a proper mount. The TR21 needs to be forward farther than most scopes.  This takes a extended riser and as low a ring as you can get and still clear the occular housing adjustments.  5" of eye relief is typical for most shooters (rear of scope needs to be about even with the back edge of the trigger).  Te key to this scope is to learn to shoot targets close up occluded style.  For long range, get down on the stock and look through it. For close range, look slightly over the top (soft cheekweld). With both eyes open you see the red triangle floating on the target, no magnification. It's very fast for close up targets, out to 50 yards. Beyond that, tighten it up and look through, using the magnification.  It takes a little practice, but works very well.

I like a zero at 275 yards.  Never more that 4" high from the muzzle out to 275, only 4" low at 350. Covers virtually all typical 3-Gun ranges with no worries.

Email if I can help further.