Does anyone find it necessary to use small base sizing dies?
Can you neck size only or is FL resize a must?
Is it better to crimp your bullets?
Small base die for an AR? It depends.
Cases fired in your rifle, a standard full length die should be fine.
With the variability of 223 Remington.5.56 NATO chambers and the manufacturing tolerances of dies, you can get into a situation where cases fired in one rifle and full length sized will not fit into the chamber of a different rifle.
How do I know, I have such a combination of rifles and a particular full length resizing die.
Adjusting the die, short of maybe machining off the base of the die, makes no difference. The die bumps the shoulder more than adequately for both rifles.
My advice, if you have a standard full length sizing die, stick with it but be aware of potential problems when sizing cases fired in another rifle. After a while, you will know how finicky your rifle's chamber is.
If you need to buy dies, I would get a small base die set and not worry about it.
I do not crimp any loads fired in my ARs.