[QUOTE=agentloveless;15746] From what I have read, the heavy subsonic loads perform similar to 22lr and therefore a 22lr scope would be good. Thanks guys.[QUOTE]Ballistics
I would question your statement that heavy subsonic loads perform similar to a 22LR. Maybe for the first 100 yards, but any 22LR bullet has a much lower ballistic coefficient than any heavy 30 caliber boattail. Here is a plot of what is essentially holdover of the bore relative to the line of sight of a scope mounted 2" above the bore for a typical AR-15 shooting a 220 SMK at 1000 fps muzzle velocity.
Whatever scope you pick needs to be able to either be adjustable over the range of elevation angle you'll be shooting or have a reticle which covers that range. If you're only shooting to maybe 200 yards then most scopes will have sufficient vertical adjustment. A standard Mil-Dot reticle has 34.38 MOA over it's 10 mil reticle. For hunting quick moving targets a low power scope with a large field of view (short eye relief) is desirable. A 300-221 has little recoil. I would not want a commercial BCD reticle or 22LR reticle on a 300 Whisper. It would always be wrong. A custom reticle would be good but they're expensive and lock you in to one bullet, one air density, and one muzzle velocity. For for best accuracy a scope with target knobs and plenty of elevation adjustment is my choice. It can be used with any bullet/velocity/atmosphere with range cards or a pocket calculator. It's downside to is that its' slower than using a custom reticle. For subsonic shooting range needs to known accurately beyond about 200 yards. The best for that is a laser rangefinder
What scope is on my 300-221 AR-15s? . They have Bushnell model 3200 10x40 mil dots. At under $200 I consider them a "best buy". They have 90 MOA of vertical adjustment with large target knobs and 1/4 MOA positive clicks. One thing they don't have is parallax adjustment, but that is unlikely to introduce a significant error compared to other error sources. An AR-15 is not a benchrest rifle. The mil-dots can be used either for ranging or for short range windage and elevation "holdovers" for quick shots. Arguably 10x is too much magnification and too small of field of view for hunting or combat at short range (100 yards or less).
A Leupold Mk 4 16x40 adds parallax adjustment and 140 MOA of vertical adjustment but costs about eight times more. No doubt its a good choice for very long range subsonic shooting (500 yards plus).
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