I've never crimped any of my rounds for my AR, but I also have never used a FMJ either or anything with a cannelure. Usually you would want to seat your rounds to the max length (closest to your lands). In an AR the standard OAL is about 2.250", 2.250" is what I use on all my rounds I load because it leaves just enough room to keep the bullet tips from rubbing on the mag. But all that stuff depends on your rifles chamber. But I can almost bet off the shelf ammo you buy is about 2.250-2.260" OAL. Maybe try a bullet without the cannelure and adjust your OAL for accuracy, if thats what your looking for.
Lock and load, the zombies (democrats) are coming (to take your guns)!