Will a 4.5-14x40 Nikon be sufficient enough for varmint hunting?

I'm looking at the Nikon 4.5-14x40 Buckmaster to put on my.223 AR. Will this give me enough power to hit a groundhog around 325 yards? Or should I go for a 4-16?

Nikon makes a good clear scope with good glass, so 14 power would likely work. Going bigger never hurts, but it's also not always needed. My Luepold 7 power on my shotgun is clearer at 200 yards that my Bsa 24 power at the same distance. The glass makes a bigger difference than the power in some cases.

It should be sufficient. You might try a bigger objective lens, say 44/50. At that distance, it wouldn't hurt. In a conventional rifle, it is always preferred to have the front bell of the scope as close to the barrel as possible. I would assume the same applies to an AR platform also. A 4x16 with a 44mm objective lens would be sweet on your rifle, I would think.

If you are going to get a Nikon scope, consider one of the ones tailored to the AR:
http://www.nikonsportoptics.com/en/Nikon-Products/Hunting-Optics/Scopes/AR-MSR/index.page

Either the M-223 series or the budget P-223 series

I own a Buckmaster 4.5-14x40 and I can tell you that it is plenty of scope to get the job done at 325 yards. They are retailing for about $300 new but you can find them cheaper used. For about that price or a few bucks more though you should be able to find a used Nikon Monarch which is nicer glass. I have also found older Leupold Vari-X III scopes for $300-$400 in a 6.5-20x40 or x50.

Yes - this scope is up to the task… The question is - are your skills and semi-auto AR15 up to the task… For over 200 yards I switch to a bolt action rifle… But I suppose if you spend the time and get the scope dialed in with decent ammo then this combination will work…

Yeah that will do it, its better to have a 14x scope that is clear than a 16x that is a little blurry.